U.S. patent application number 14/824618 was filed with the patent office on 2015-12-03 for microbial detection system and methods.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to PHILLIP A. BOLEA, KURT J. HALVERSON, CYNTHIA D. ZOOK.
Application Number | 20150344931 14/824618 |
Document ID | / |
Family ID | 44628769 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150344931 |
Kind Code |
A1 |
BOLEA; PHILLIP A. ; et
al. |
December 3, 2015 |
MICROBIAL DETECTION SYSTEM AND METHODS
Abstract
The disclosure provides culture devices and methods for a
microorganism in a sample. The devices include a base member, a
cover sheet, an adhesive layer coupled to the base member or the
cover sheet, and a cold water-soluble gelling agent disposed on the
base member; wherein the devices are substantially optically
transmissive when the gelling agent is hydrated with a clear
liquid. Methods of use include detecting or enumerating
microorganisms. The methods further provide for detecting a
microorganism by detecting the presence or size of an abiogenic gas
bubble in a culture device.
Inventors: |
BOLEA; PHILLIP A.; (GRANT,
MN) ; HALVERSON; KURT J.; (LAKE ELMO, MN) ;
ZOOK; CYNTHIA D.; (HUDSON, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
44628769 |
Appl. No.: |
14/824618 |
Filed: |
August 12, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13807058 |
Feb 7, 2013 |
9127300 |
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PCT/US11/41939 |
Jun 27, 2011 |
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14824618 |
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61360166 |
Jun 30, 2010 |
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Current U.S.
Class: |
435/297.1 |
Current CPC
Class: |
C12M 23/04 20130101;
C12Q 1/24 20130101; C12M 41/36 20130101; C12M 25/14 20130101; C12Q
1/04 20130101 |
International
Class: |
C12Q 1/04 20060101
C12Q001/04 |
Claims
1. A device for detecting microorganisms, comprising: a base
member; a cover layer; a cold water soluble gelling agent disposed
on the adhesive layer wherein the device is substantially optically
transmissible when the gelling agent is hydrated with a clear
aqueous liquid.
2. The device of claim 1, further comprising a first adhesive layer
coupled to one of the base member or the cover layer.
3. The device of claim 2, further comprising a second adhesive
layer coupled to the other of the base member or cover layer.
4. The device of claim 2, further comprising an optical filter
layer or a contrast layer.
5. The device of claim 2, wherein the optical haze of the culture
device after hydration of the device with a clear aqueous liquid is
.ltoreq.95% when measured according to ASTM 1003.
6. The device of claim 2, wherein the optical clarity of the
culture device after hydration of the device with a clear aqueous
liquid is .gtoreq.10% when measured according to ASTM 1003.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/807,058, filed Feb. 7, 2013, which is a national stage
filing under 35 U.S.C. 371 of PCT/US2011/041939, filed Jun. 27,
2011, which claims priority to U.S. Provisional Patent Application
No. 61/360,166, filed Jun. 30, 2010, the disclosure of which is
incorporated by reference in its entirety herein.
BACKGROUND
[0002] Traditional culture methods to detect bacteria in a sample
typically rely on the contrast between bacterial colonies and the
components of the device (e.g., containment vessel, nutrient
medium, and gelling agent) to detect the presence and, optionally,
the identity of a microorganism in the sample.
[0003] There exists a need for simple articles and methods for the
detection of bacteria in a sample.
SUMMARY
[0004] In view of the current general methods to detect the
presence or absence of a microorganism in a sample, the inventive
culture devices provide methods for rapid, indicatorless detection
of a microorganism in a sample. Advantageously, the inventive
devices and methods can be used without indicator reagents, some of
which are known to have inhibitory effects on the growth of
microorganisms. Additionally, or alternatively, some embodiments of
the devices and methods provide for the enumeration of bacteria. In
some embodiments, the inventive methods provide for the automated
detection and/or enumeration of bacteria.
[0005] Thus, in one aspect, the present disclosure provides methods
for detecting the presence or absence of a microorganism in a
sample. The method can comprise providing a liquid sample and a
culture device comprising a base member, a cover layer, and a dry
cold water-soluble gelling agent disposed on the base member and/or
the cover sheet. The culture device can include an outermost first
major surface, an outermost second major surface, and a growth
area. The culture device can be configured to form a highly
transmissive optical path extending from the outermost first major
surface to the outermost second major surface. The method further
can comprise hydrating the growth area of the device with the
sample, incubating the device for a period of time, illuminating
the growth area with a light source, and detecting the presence or
absence of a microorganism in the growth area. Detecting the
presence or absence of a microorganism can comprise observing an
indication of growth. In some embodiments of the methods, the
culture device further can comprise an adhesive layer coupled to
the base member and/or the cover sheet, wherein the gelling layer
is disposed on the adhesive layer(s).
[0006] In some embodiments of the methods, illuminating the growth
area can comprise illuminating the growth area with the light
source positioned facing the first major surface of the culture
device. In any of the above embodiments of the method, observing an
indication of growth can comprise observing the growth area from an
observation position facing the first major surface of the culture
device.
[0007] In some embodiments of the methods, illuminating the growth
area can comprise illuminating the growth area with the light
source positioned facing the second major surface of the culture
device.
[0008] In some embodiments, the methods further can comprise
providing a first contrast layer; and prior to detecting the
presence or absence of a microorganism, positioning the first
contrast layer proximate the second major surface of the culture
device. In some embodiments, the methods further can comprise
providing a second contrast layer and, prior to detecting the
presence or absence of a microorganism, positioning the second
contrast layer proximate the second major surface of the culture
device.
[0009] In any of the above embodiments, detecting the presence or
absence of a microorganism can comprise detecting the scattering,
absorbance or transmittance of light. In any of the above
embodiments, the methods further can comprise adding an indicator
reagent, wherein detecting the presence or absence of a
microorganism comprises detecting an observable change in the
indicator reagent. In any of the above embodiments, detecting the
presence or absence of a microorganism can comprise detecting a
fluorescent signal.
[0010] In another aspect, the present disclosure provides methods
for detecting the presence or absence of a microorganism in a
sample, comprising providing a sample and a culture device
comprising a base member, a cover layer, and a hydrogel comprising
a plurality of abiogenic gas bubbles disposed there between;
wherein the hydrogel defines a growth area. The culture device can
include an outermost first major surface, an outermost second major
surface. The methods further comprise inoculating the growth area
of the device with the sample at a first point in time, incubating
the device for a period of time, illuminating the growth area with
a light source, and detecting the presence or absence of a
microorganism in the growth area at a second point in time.
Detecting the presence or absence of a microorganism can comprise
observing an indication of growth. Observing an indication of
growth can comprise detecting the diminution or absence of at least
one abiogenic gas bubble in the hydrogel at the second point in
time.
[0011] In some embodiments of the methods, providing the culture
device can comprise providing a thin film culture device that
includes a dry, cold water-soluble gelling agent, wherein the
method further comprises hydrating the gelling agent with an
aqueous liquid. In any of the embodiments, the aqueous liquid can
comprise the sample.
[0012] In some embodiments, the methods further can comprise
observing the growth area with regard to the diminished size or
absence of the gas bubble at a third point in time and comparing
the observations at two points in time. In any of the embodiments,
the methods further can comprise providing a first contrast layer
and, prior to detecting the presence or absence of a microorganism,
positioning the first contrast layer proximate the second major
surface of the culture device.
[0013] In some embodiments, the methods further can comprise
providing a second contrast layer and prior to detecting the
presence or absence of a microorganism, positioning the second
contrast layer proximate the second major surface of the culture
device. In any of the embodiments, detecting the presence or
absence of a microorganism can comprise detecting the scattering,
absorbance or transmittance of light. In any of the above
embodiments, the methods further can comprise adding an indicator
reagent, wherein detecting the presence or absence of a
microorganism comprises detecting an observable change in the
indicator reagent. In any of the embodiments, detecting the
presence or absence of a microorganism can comprise enumerating
microorganisms. In any of the embodiments, the methods further can
comprise providing a first optical filter and, prior to detecting
the presence or absence of a microorganism, positioning the first
optical filter between the light source and the culture device. In
any of the above embodiments, detecting the presence or absence of
a microorganism can comprise detecting and differentiating two or
more types of microorganisms.
[0014] In any of the above embodiments, the methods further can
comprise providing an imaging system and obtaining an image of the
growth area of the culture device, wherein observing an indication
of growth comprises displaying, printing, or analyzing the image of
the growth area.
[0015] In another aspect, the present disclosure provides devices
for detecting microorganisms; comprising a base member, a cover
layer, and a cold water soluble gelling agent disposed on the first
adhesive layer. The devices are substantially optically
transmissible when the gelling agent is hydrated with a clear
aqueous liquid. In some embodiments, the device further can
comprise a first adhesive layer coupled to one of the base member
or the cover layer.
[0016] In any of the above embodiments, the devices can further
comprise a second adhesive layer coupled to the other of the base
member or cover layer. In any of the above embodiments, the devices
further can comprise a nutrient medium disposed on the first or
second adhesive layer. In any of the above embodiments, the devices
further can comprise an optical filter layer or a contrast
layer.
[0017] In any of the above embodiments, the optical haze of the
culture device, after hydration with a clear aqueous liquid, is
.ltoreq.95% when measured according to ASTM 1003. In any of the
above embodiments, the optical clarity of the culture device, after
hydration with a clear aqueous liquid, is .gtoreq.10% when measured
according to ASTM 1003.
[0018] The words "preferred" and "preferably" refer to embodiments
of the invention that may afford certain benefits, under certain
circumstances. However, other embodiments may also be preferred,
under the same or other circumstances. Furthermore, the recitation
of one or more preferred embodiments does not imply that other
embodiments are not useful, and is not intended to exclude other
embodiments from the scope of the invention.
[0019] As used herein, "a," "an," "the," "at least one," and "one
or more" are used interchangeably. Thus, for example, a sample
suspected of containing "a" microorganism can be interpreted to
mean that the sample can include "one or more" microorganisms.
[0020] The term "and/or" means one or all of the listed elements or
a combination of any two or more of the listed elements.
[0021] Also herein, the recitations of numerical ranges by
endpoints include all numbers subsumed within that range (e.g., 1
to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). The above
summary of the present invention is not intended to describe each
disclosed embodiment or every implementation of the present
invention. The description that follows more particularly
exemplifies illustrative embodiments. In several places throughout
the application, guidance is provided through lists of examples,
which examples can be used in various combinations. In each
instance, the recited list serves only as a representative group
and should not be interpreted as an exclusive list.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The invention will be further explained with reference to
the drawing figures listed below, where like structure is
referenced by like numerals throughout the several views.
[0023] FIG. 1 is a top perspective view, partially in section, of
one embodiment of a culture device configured to form a
highly-transmissive optical path, according to the present
disclosure.
[0024] FIG. 2 is a top view, partially in section, of one
embodiment of a culture device with a contrast layer according to
the present disclosure.
[0025] FIG. 3 is a top view of one embodiment of a culture device
comprising a hydrogel with a plurality of abiogenic gas bubbles
distributed therein at a first point in time, according to the
present disclosure.
[0026] FIG. 4a is a top view of the culture device of FIG. 3 at a
second point in time.
[0027] FIG. 4b is an enlarged view of a portion of the culture
device of FIG. 4a.
[0028] FIG. 5a is a top view of the culture device of FIG. 3 at a
third point in time.
[0029] FIG. 5b is an enlarged view of a portion of the culture
device of FIG. 5a.
[0030] FIG. 6 is a side view of one embodiment of the detection of
a microbial colony in a culture device configured to form a
highly-transmissive optical path, according to the present
disclosure.
[0031] FIG. 7 is a side view of another embodiment of the detection
of a microbial colony in a culture device configured to form a
highly-transmissive optical path, according to the present
disclosure.
[0032] FIG. 8 is a block diagram of one embodiment of a detection
system according to the present disclosure.
[0033] FIG. 9 is a bar graph of optical clarity measurements of
thin film culture devices comprising a gelling agent.
DETAILED DESCRIPTION
[0034] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the accompanying drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways. Also, it is to be understood that the phraseology and
terminology used herein is for the purpose of description and
should not be regarded as limiting. The use of "including,"
"comprising," "containing," or "having" and variations thereof
herein is meant to encompass the items listed thereafter and
equivalents thereof as well as additional items. Unless specified
or limited otherwise, the terms "supported," and "coupled" and
variations thereof are used broadly and encompass both direct and
indirect supports and couplings. It is to be understood that other
embodiments may be utilized and structural or logical changes may
be made without departing from the scope of the present disclosure.
Furthermore, terms such as "front," "rear," "top," "bottom," and
the like are only used to describe elements as they relate to one
another, but are in no way meant to recite specific orientations of
the apparatus, to indicate or imply necessary or required
orientations of the apparatus, or to specify how the invention
described herein will be used, mounted, displayed, or positioned in
use.
[0035] The present disclosure is generally directed to methods and
articles for detecting microorganisms in a sample. In some
embodiments, the articles and methods employ substantially
optically-transmissive culture devices. The low haze-high clarity
devices provide the high contrast needed to distinguish a colony of
microorganisms from the materials of the culture device and provide
the high spatial resolution to distinguish two microbial colonies
that are located very close to one another. In some embodiments,
the methods employ the observation of the diminution or
disappearance of one or more abiogenic gas bubbles in a culture
device as an early indication (e.g., before the appearance of a
visible colony) of the presence of a microorganism in a culture
device.
[0036] The articles and methods are used to detect microorganisms
in a sample. Suitable samples can be obtained or derived from a
variety of sources. The term "source" is generally used to refer to
the food or nonfood desired to be tested for microorganisms. The
source can be a solid, a liquid, a semi-solid, a gelatinous
material, gas (e.g., air), and combinations thereof. In some
embodiments, the source can be provided by a capture element that
was used, for example, to collect the source from a surface of
interest or from air. In some embodiments, the liquid composition
can include the capture element, which can be further broken apart
(e.g., during an agitation or dissolution process) to enhance
retrieval of the source and any microorganism of interest. The
surface of interest can include at least a portion of a variety of
surfaces, including, but not limited to, walls (including doors),
floors, ceilings, drains, refrigeration systems, ducts (e.g., air
ducts), vents, toilet seats, handles, doorknobs, handrails,
countertops, tabletops, eating surfaces (e.g., trays, dishes,
etc.), working surfaces, equipment surfaces, clothing, etc., and
combinations thereof. All or a portion of the source can be used in
the method. When a portion of the source is used, this can
sometimes be referred to as a "sample" of the source. However, the
term "sample" is generally used herein to refer to the portion of
volume or mass of material that is obtained from the source and is
introduced into a test device for the detection of
microorganisms.
[0037] The term "food" is generally used to refer to a solid,
liquid (e.g., including, but not limited to, solutions,
dispersions, emulsions, suspensions, etc., and combinations
thereof) and/or semi-solid comestible composition. Examples of
foods include, but are not limited to, meats, poultry, eggs, fish,
seafood, vegetables, fruits, prepared foods (e.g., soups, sauces,
pastes), grain products (e.g., flour, cereals, breads), canned
foods, milk, other dairy products (e.g., cheese, yogurt, sour
cream), fats, oils, desserts, condiments, spices, pastas,
beverages, water, animal feed, other suitable comestible materials,
and combinations thereof.
[0038] "Sample acquisition device" is used herein in the broadest
sense and refers to an implement used to collect a liquid,
semisolid, or solid sample material. Nonlimiting examples of sample
acquisition devices include swabs, wipes, sponges, scoops,
spatulas, tongue depressors, filters, pipettes, pipette tips, and
siphon hoses.
[0039] "Substantially optically-transmissive", as used herein,
refers to an optical path in which the optical haze, as measured by
ASTM Method 1003, is less than or equal to about 95% and the
optical clarity, as measured by ASTM Method 1003, is greater than
or equal to about 10%.
[0040] An "abiogenic gas bubble", as used herein, refers to an
optically-detectable gas bubble that is produced by means other
than biological activity. "Optically-detectable" is used in the
broadest sense and includes visual detection by a human as well as
detection by machine vision.
Culture Devices:
[0041] The present disclosure in certain embodiments includes
culture devices for the detection of bacteria. Culture devices of
the present invention include, for example, thin film culture plate
devices. Thin film culture plate devices are typically more compact
than traditional agar petri dishes and typically contain dry,
rehydratable culture medium to support the growth of certain
microorganisms. Non-limiting examples of thin film culture plate
devices include the coated-substrate devices disclosed in U.S. Pat.
Nos. 4,565,783; 5,089,413, and 5,681,712; each of which is
incorporated herein by reference in its entirety.
[0042] FIG. 1 illustrates an embodiment of a culture device 110 in
accordance with the present disclosure. The culture device 110
comprises a base 112 and a cover sheet 122. The culture device 110
includes an outermost first major surface 104 and an outermost
second major surface 106. The culture device 110, when inoculated
with a liquid sample, is configured to form a highly transmissive
optical path extending from the first major surface to the second
major surface.
[0043] Optionally, the base 112 and the cover sheet 122 can be
coupled together (e.g., in a hinge region 108 using any suitable
coupling means (not shown) known in the art, such as a staple, an
adhesive, an adhesive tape, double-sided adhesive tape or the
like). At least a portion of either the base 112 and/or the cover
sheet 122 comprises a coating. As shown in FIG. 1, the base 112
comprises a coating that includes an optional adhesive layer 114
and a gelling layer 116. Optionally, the culture device may further
include a spacer 118. The spacer 118 includes an aperture 120,
which defines the boundary of a growth area 126.
[0044] In the illustrated embodiment, the growth area 126 is
circular. The walls of aperture 120 provide a well of predetermined
size and shape (e.g., circle, oval, square, rectangle, etc.) to
confine a liquid sample (not shown) deposited therein. The aperture
120 generally delineates the boundary of a growth area 126 of the
culture device 110. Spacer 118 should be thick enough to form a
well of the desired volume, e.g., 1, 2 or 3 milliliters. Closed
cell polyethylene or polystyrene foams are preferred materials for
spacer 118, but any material which is hydrophobic (non-wetting),
inert to microorganisms, and capable of withstanding sterilization
may be used. In some embodiments (not shown), the spacer 118 can
comprise a plurality of apertures 20 (e.g., 2, 3, 4, 5, 6, 7, 8, 9,
10, 12, 15, or 20 apertures), each of which can be inoculated with
a distinct liquid sample.
[0045] The thickness of spacer 118 should be sufficient to enclose
the liquid volume added to the culture device when the device is
inoculated. Depending upon the thickness of the membrane, when
used, the spacer 118 can be at least about 0.5 mm thick, about 1 mm
thick, about 1.5 mm thick and about 2 mm thick.
[0046] The base 112 and cover layer 122 are fabricated using an
optically-transmissive material. Preferably, the base 112 and cover
layer 122 are transparent. Suitable materials for the base 112 and
cover layer 122 include, for example, polyethylene, polypropylene,
polycarbonate or polyester films, for example. The major surfaces
of the base 112 and cover layer 122 should be substantially flat
and smooth and should not include surface features (e.g., pits,
bumps, ridges, embossed patterns) that reduce optical clarity by
scattering light, for example.
[0047] Optional adhesive layer 114 can comprise a variety of
adhesives (e.g., pressure-sensitive adhesives) known in the art.
Examples of suitable adhesives include copolymer silicone adhesives
(e.g., the silicone adhesives described in U.S. Pat. No. 6,703,120,
for example, which is incorporated herein by reference in its
entirety) and acrylate adhesives (e.g., the acrylate adhesives
described in U.S. Pat. No. 4,565,783, for example, which is
incorporated herein by reference in its entirety). The adhesive
layer 114 can be applied to the base member 112 and/or the cover
sheet 122 using processes known in the art (e.g., knife-coating,
extrusion, laminative transfer from a release liner, etc.). When
applying the adhesive layer 114 to the base member 112 and/or cover
sheet 122, care must be taken to minimize the introduction of
light-scattering features into (e.g., bubbles) or onto (e.g.,
craters, pits, bumps, ridges, valleys, channels, or the like)
because such features can reduce the optical clarity of the culture
device 110.
[0048] Thus, the base member 112, cover sheet 122, and adhesive
layer 114 are selected from materials with high optical clarity and
are processed in a manner to provide a high degree of optical
clarity in the culture device 110. Optical clarity can be measured
by methods that are known in the art. Optical transmittance is
related to optical clarity and can be measured can be measured
using ASTM Method 1003, for example. Percent clarity is related to
optical clarity and can be measured can be measured using ASTM
Method 1003, for example. Percent haze is related to optical
clarity and can be measured can be measured using ASTM Method 1003,
for example.
[0049] The gelling agent used in the gelling layer 116 comprises a
cold water-soluble gelling agent. Suitable cold water-soluble
gelling agents include, for example, guar gum, xanthan gum, locust
bean gum, hydroxyethylcellulose, carboxymethylcellulose,
polyacrylamide, algin, and a combination of any two or more of the
foregoing. After a liquid sample is deposited between the base
member 112 and the cover sheet 122, the liquid causes the gelling
agent to swell, thereby forming a hydrogel containing the liquid
sample.
[0050] In any of the embodiments, the gelling layer 116 may further
comprise a nutrient to facilitate the growth of a microorganism. In
any of the embodiments, the gelling layer 116 may further comprise
a selective agent to select for the growth of a specific
microorganism or group of microorganisms. In some embodiments, the
gelling agent, optional nutrients and optional selective agents can
be powder-coated onto the adhesive layer 114, as described in U.S.
Pat. No. 4,565,783, for example.
[0051] In another embodiment of the invention, powder 116 may
comprise a coating that includes a mixture of a gelling agent and a
nutrient, a selective agent, and/or an indicator reagent which has
been dissolved or suspended in a solution, coated and dried onto
substrate 112. In this embodiment, the coating is substantially
water-free (i.e., the coating has a water content no greater than
about the water content of the dehydrated coating once it has been
permitted to equilibrate with the ambient environment).
[0052] The specific nutrients and/or selective agents used in the
culture device will be apparent to those skilled in the art in view
of the present specification and may be optimized for the
particular bacteria to be grown and/or to be selectively detected
or inhibited. For example, certain selective agents (e.g.,
antibiotics such as vancomycin) may be added to the composition to
select for corresponding antibiotic-resistant microorganisms.
Additionally, the concentration of the selective agent can be
adjusted to select for a certain level of resistance, which is well
known to a person of ordinary skill in the art.
[0053] Culture devices of the present disclosure may optionally
include an indicator reagent. The indicator reagent may be
incorporated into the gelling layer, as described above, and/or
incorporated into the adhesive layer, as described in U.S. Pat. No.
4,565,783, for example.
[0054] An exemplary useful class of indicator reagents include dyes
that are metabolized by, or otherwise react with, growing
microorganisms, and in so doing cause the microbial colonies to be
colored or fluoresce for ease of detection and/or quantitation by a
technician or by an automated reader. Nonlimiting examples of such
dyes include triphenyltetrazolium chloride, p-tolyltetrazolium red,
tetrazolium violet, veratryl tetrazolium blue, and
5-bromo-4-chloro-3-indolyl phosphate disodium salt. However, it
will be appreciated that other suitable dyes can be used depending
on the particular organism(s) to be identified.
[0055] A buffering reagent, such as sodium carbonate, can be
employed to provide a medium exhibiting a neutral pH and "Cab-O-Sil
M-5" can be employed as a processing aid for powder-coated
mixtures, as described in U.S. Pat. No. 4,565,783, which is
incorporated herein by reference in its entirety. Of course, the
particular coating mixture (e.g., nutrients, indicator reagents,
and/or gelling agents) used for powder 116 may be adjusted
depending upon the type of microorganisms to be grown.
[0056] It is contemplated that articles of the present disclosure
can include differential indicator reagents. As used herein,
"differential indicator reagent" refers to a reagent added to the
medium that will indicate the presence of certain microorganisms
and not other microorganisms. Nonlimiting examples of differential
indicator reagents include dyes (e.g., stains, pH indicators, redox
indicators), enzyme substrates (e.g., chromogenic or fluorogenic
substrates for phosphatases, glycosidases, peptidases, nucleases,
lipases, and the like), and specific nutrients (e.g., fermentable
carbohydrates, amino acids) which, when metabolized by certain
microorganisms, produce a detectable reaction (e.g., a pH indicator
changing color within or adjacent a colony).
[0057] In some embodiments, one or more differential indicator
reagents can be added to the thin film culture device in the
water-based composition that is coated onto the substrate. In some
embodiments, one or more differential indicator reagents can be
added to the liquid sample that is added to the culture device.
[0058] In the embodiments (not shown) wherein the culture device
does not include a spacer 118 to confine the sample during
inoculation, a template, e.g., a weighted ring (not shown), may be
applied temporarily to the outside of cover sheet, after closing,
to confine the sample to a specific region while the
cold-water-soluble powder forms a gel. The portion of the culture
device inoculated with a sample generally delineates the growth
area 126 of the device. In one embodiment, a thin film culture
plate device can be made by producing a liquid coating mixture,
coating the liquid coating mixture onto a substrate, drying the
coated substrate and, optionally, attaching a cover sheet according
to processes described in U.S. Pat. No. 4,565,783, for example.
[0059] In use, a predetermined amount of inoculum, typically about
one milliliter of a liquid inoculum is added to the device by
pulling back cover sheet 122 and depositing the inoculum onto the
gelling layer 116. The inoculum may optionally comprise a nutrient,
a selective agent, an indicator reagent or a combination of any two
or more of the foregoing. Cover sheet 122 is then replaced over the
base member 112 and the inoculum is evenly spread inside the
opening of the spacer 118, if present. A convenient tool to do this
is a generally flat, weighted article that is shaped and
dimensioned to conform to the growth area 126 of the culture device
110. The inoculated device 110 is then incubated for a
predetermined time after which the number of bacterial colonies
growing on the substrate may be observed through the cover sheet
122 and counted.
[0060] A preferred coating mixture, when hydrated with a
pre-determined volume of sample, can comprise the ingredients of
the culture medium at the concentrations shown in Table 1. In some
embodiments, the coating mixture for the culture device can
comprise some of the ingredients shown in Table 1 and a liquid
(e.g., a diluent) containing the sample can comprise some or all of
the remaining ingredients shown in Table 1. Thus, the addition of
the ingredients in the culture device and the ingredients in the
diluent can result in the culture medium shown in Table 1.
TABLE-US-00001 TABLE 1 Composition of an exemplary culture medium.
Ingredient Amount (milligrams/mL) Tryptone 3.3 Proteose Peptone No.
3 10 Bacto Peptamin 10 Yeast Extract 7.3 Dextrose 20.6 Sodium
Pyruvate 6.6 Meat Extract 15 K.sub.2HPO.sub.4 3.3 KH.sub.2PO.sub.4
0.4 Guar gum 25-50
[0061] Optionally, the culture medium can comprise a buffer.
Suitable buffers include phosphate buffers. In some embodiments,
the carbonate buffer is a sodium carbonate buffer. In some
embodiments, the phosphate buffer is a potassium phosphate buffer.
In some embodiments, the culture medium can comprise more than one
buffering agent (e.g., potassium phosphate and sodium acetate). The
phosphate buffer can be about 22 mM.
[0062] The concentration of each component in the culture medium is
selected to provide a concentration suitable for growth and/or
detection of the target microorganisms after the culture device has
been inoculated. Suitable concentrations of nutrients and selective
agents for growing specific microorganisms in culture media are
known in the art.
[0063] The selection of target microorganisms may include
inhibiting the growth of non-non-target microorganisms, promoting
the growth of non-target microorganisms, or both. Promoting the
growth of target microorganisms may be provided by the at least one
first selective agent either directly (e.g., a nutrient that can be
used by target microorganisms and not by other microorganisms),
indirectly (e.g., by reducing competition for nutrients by
inhibiting non-target microorganisms), or both directly and
indirectly. Any element, radical, ion, or compound that selects for
the growth of target microorganisms may be suitable for use as a
selective agent.
[0064] A dry culture medium according to the present invention may
be applied to one or more surfaces of a thin film culture device in
the following manner. The components of the culture medium may be
dissolved in a solvent (e.g., water). The resulting solution may
then be coated onto one or more surfaces of the device. The coating
is then allowed to dry, leaving dried culture medium on the
surfaces of the device that had been coated with the culture medium
solution. The coating may be dried in any suitable manner
including, but not limited to, air drying and heating.
[0065] The quantity of each component of the dry culture medium is
at least partially determined by at least two factors: (1) the
concentration of that component in the culture medium solution, and
(2) the amount of the solution coated onto a given surface area of
the culture device (the coating weight). Suitable coating weights
may range from about 0.45 mg/cm.sup.2 to about 2.5 mg/cm.sup.2. In
some embodiments, the culture medium nutrients may be coated
separately from the indicator reagents. In such embodiments, the
coating weight for the culture medium nutrients may range from
about 1.6 mg/cm.sup.2 to about 2.5 mg/cm.sup.2. In one embodiment,
the coating weight of the nutrient coating is about 2.1
mg/cm.sup.2. The coating weight for the indicator coating may range
from about 0.45 mg/cm.sup.2 to about 0.84 mg/cm.sup.2. In one
embodiment, the coating weight of the indicator coating is about
0.62 mg/cm.sup.2.
[0066] Turning back to the drawings, FIG. 2 shows another
embodiment of a culture device 210 according to the present
disclosure. The device 210 comprises a base member 212, cover sheet
222, adhesive layer 214, optional spacer 218, and gelling layer
216, as described for the culture device 110 of FIG. 1. In
addition, the culture device 210 further comprises a contrast layer
230 positioned proximate the second major surface of the culture
device 210
[0067] The contrast layer 230 can be fabricated from any suitable
material to reflect, absorb, or diffuse (e.g., scatter) selected
wavelengths of light. Suitable materials include, for example,
cellulosic material, metal, glass, organic polymers or inorganic
polymers. The materials may be blended with compounds (e.g.,
pigments, dyes, particles) that absorb, reflect, or diffuse
selected wavelengths of light. The contrasting layer 230 may
comprise a uniform surface facing the culture device 210.
[0068] In some embodiments, the contrast layer 230 may comprise a
reflective layer, such as metal, metal foil, a metalized polymeric
film, or a mirror, for example. In some embodiments, the contrast
layer 230 may comprise a specularly-reflective layer, such as the
specularly-reflective film. An example of a suitable
specularly-reflective layer is a Vikuiti Enhanced Specular
Reflective (ESR) Film (part number 98044027500) obtained from 3M
Company in St. Paul, Minn.
[0069] In some embodiments, the contrast layer 230 may be coupled
(e.g., adhesively coupled) to the culture device 210. In an
alternative embodiment, the contrast layer 230 may be a composition
that is coated onto the base member 212 of the culture device
210.
Samples
[0070] Suitable test samples can be derived from any source.
Samples of interest may include liquids (e.g., beverages, process
streams, water), solids (e.g., food ingredients, plants, meat, air,
surfaces (e.g., floors, walls, instruments, food-processing
equipment), and the like. Samples can also include cultured cells
(e.g., bacterial cultures, enrichment broths).
[0071] Various sampling techniques for the detection of microbes on
surfaces are known. Such sampling techniques are suitable for the
methods of the present invention as well. For example, it is common
to obtain a sample from wiping the surface of food processing
equipment or from wiping the nares of a patient. A particularly
preferred sampling technique includes contacting (e.g., swabbing,
wiping) the surface with a sterile swab, sponge, or sampling
device.
[0072] A wide variety of swabs or other sample collection devices
are commercially available, for example, from 3M Company, St. Paul
Minn., under the trade designation 3M.TM. Quick Swab, from Puritan
Medical Products Co. LLC, Guilford, Me., under the trade
designation PURE-WRAPS or from Copan Diagnostics, Inc. Corona,
Calif., under the trade designation ESWAB, or from microRheologics,
S.r.l., Brescia, IT, under the trade designation FLOCKEDSWAB. A
sample collection means such as that disclosed, for example, in
U.S. Pat. No. 5,879,635 (Nason) can also be used if desired. Swabs
can be of a variety of materials including cotton, rayon, calcium
alginate, Dacron, polyester, nylon, polyurethane, and the like.
[0073] The sample collection device (e.g., swab) can then be
cultured directly, analyzed directly, or extracted (e.g., by
washing, elution by vortexing) with an appropriate solution. Such
extraction (i.e., elution) solutions typically include water and
can optionally include a buffer and at least one surfactant. An
example of an elution buffer includes, for example, phosphate
buffered saline (PBS), which can be used in combination, for
example, with TWEEN 20 or PLURONIC L64. The test sample (e.g.,
liquid) may be subjected to treatment prior to further analysis.
This includes concentration, precipitation, filtration,
centrifugation, dialysis, dilution, inactivation of natural
components, addition of reagents, chemical treatment, etc.
Methods for Detecting a Microorganism in a Sample
[0074] The present disclosure provides methods for detecting
bacteria in a sample. In some embodiments, the method comprises
providing a liquid sample and a culture device comprising a base
member, a cover layer, and adhesive layer coupled to the base
member and or cover sheet, and a dry cold water-soluble gelling
agent disposed on the adhesive layer, the device configured to form
a highly transmissive optical path.
[0075] In any embodiment, the method further can comprise hydrating
the growth area of the device with the sample. The sample
originally may be a liquid sample (e.g., milk, process water)
and/or or a solid sample (e.g., food, food ingredients,
environmental residues). The liquid or solid sample may be
dissolved or suspended in a liquid medium (e.g., water, a buffer).
The culture device is opened (e.g., by lifting the cover sheet to
separate it from at least a portion of the base member) and the
liquid containing the sample is transferred (e.g., pipetted or
poured) into the growth area between the base member and the cover
sheet, thereby bringing the liquid sample into contact with the
gelling agent. After contact with the liquid sample, the gelling
agent hydrates to for a hydrogel.
[0076] In any embodiment, the method further can comprise
incubating the device for a period of time. The period of time may
be a predetermined period of time. In some embodiments, the culture
device can be incubated for at least about 8 hours, at least about
12 hours, at least about 18 hours, at least about 24 hours, at
least about 48 hours, or at least about 72 hours. In some
embodiments, the culture device can be incubated not more than
about 24 hours, not more than about 48 hours, or not more than
about 72 hours. The incubation temperature is selected according to
the microorganism to be detected. A person of ordinary skill in the
art will select an appropriate incubation temperature (e.g., about
25.degree. C., about 30.degree. C., about 35.degree. C., about
37.degree.) for the microorganism to be detected.
[0077] In any embodiment, the method further comprises detecting
the presence or absence of a microorganism in the growth area.
Detecting the presence or absence of a microorganism comprises
illuminating the growth area with a light source. In some
embodiments, the light source (e.g., a white light) may provide a
relatively broad-spectrum of wavelengths. In some embodiments, the
light source may provide a relatively narrow band of selected
wavelengths (e.g., an optically-filtered white light or an
ultraviolet light).
[0078] In any embodiment, the method further comprises observing an
indication of growth. In some embodiments, the indication of growth
may be observed by a person visually. In some embodiments, the
indication of growth may be observed using an imaging device. In
some embodiments, the imaging device may be display or print an
image of the growth area such that a person can visually observe
and analyze the displayed or printed image. In some embodiments,
the imaging device may analyze an image of the growth area using a
processor and the results of the analysis can be stored in
electronic memory, displayed, and/or printed.
[0079] Observing an indication of growth includes observing an
object in the highly-transmissive optical path of the culture
device. For example, the object may be a microbial colony that
reflects, absorbs, or refracts light from the light source. The
colony may be observed as a bright spot, a dark spot, or a colored
spot that contrasts with the hydrogel proximate the colony.
Advantageously, selecting the components of the optical device
(e.g., the base member, adhesive layer, and cover sheet) for high
optical transmissivity, provides enhanced contrast in order to
detect microbial colonies at a relatively early stage of growth.
FIG. 6 shows one embodiment of detecting the presence or absence of
a microorganism in a sample according to the present disclosure.
The embodiment includes providing a culture device 610 (shown in
side view) configured to form a highly-transmissible optical path
extending from an outermost first major surface 604 to an outermost
second major surface 606. The culture device 610 includes a base
member 612, an optional adhesive layer 614 coupled to the base
member 612, a cover sheet 622, and a hydrogel 617 (e.g., a hydrated
gelling layer) disposed between the adhesive layer 614 and the
cover sheet 622. In the illustrated embodiment, the hydrogel 617 is
hydrated with a liquid sample.
[0080] The culture device 610 is illuminated by photons from a
light source 670. The photons can generally pass through the
optically-transmissive culture device 610. A microorganism present
in the original sample can form a microbial colony 660 in the
hydrogel 617 of the culture device 610. Photons from the light
source 670 can strike the microbial colony 660 where they can be
reflected (shown as photon "A", which is reflected toward observer
690) or absorbed, causing an observable bright spot, dark spot or
colored spot that contrasts with the brightness and/or color of the
components of the culture device 610 (e.g., the cover layer, the
gelling layer, the adhesive layer, and/or the base member). In the
illustrated embodiment, the light source is positioned facing the
first major surface 604 of the culture device 610. In the
illustrated embodiment, observing an indication of growth comprises
observing the growth area from an observation position (i.e.,
observer 690) facing the first major surface of the culture
device.
[0081] In some embodiments of the method, observing an indication
of microbial growth further comprises providing an optical filter
650 and positioning the optical filter 650 between the light source
670 and the culture device 610. In these embodiments, the culture
device 610 can be illuminated with selected wavelengths of light
(e.g., red wavelengths, blue wavelengths, ultraviolet wavelengths).
This configuration can be particularly advantageous when the color
of a microbial colony 660 is only slightly different from the color
of one or more components of the culture device 610.
[0082] In some embodiments of the method (not shown), observing an
indication of microbial growth can comprise observing the culture
device with the observer facing the second major surface of the
culture device. In these embodiments (i.e., where the light source
faces the first major surface of the culture device, and the
observer faces the second major surface of the culture device,
detecting the presence or absence of a microorganism can comprise
detecting the scattering, absorbance or transmittance of light by a
colony of microorganisms and/or by an indicator reagent.
[0083] In some embodiments of the method, observing an indication
of microbial growth further comprises providing a contrast layer
630 and, prior to observing the culture device 610, positioning the
contrast layer 630 proximate the second major surface 606 of the
culture device 610. In these embodiments, the contrast layer 630
substantially reflects or absorbs the photons from the light source
670 and thereby increasing the contrast between the microbial
colony 660 and one or more of the components of the culture device
610. Suitable contrast layers 630 of these embodiments include any
of the contrast layers described herein. The contrast layer 630 can
be positioned such that it overlaps all or any portion of the
growth area (not shown) of the culture device 610.
[0084] In some embodiments of the method (not shown), observing an
indication of microbial growth further comprises, prior to
observing the culture device, positioning a second contrast layer
proximate the second major surface of the culture device,
illuminating the culture device from a light source positioned
facing the first major surface of the culture device, and observing
an indication of microbial growth. These embodiments may be
particularly advantageous in detecting two distinct microorganisms
(e.g., distinct species; distinct genera; and distinct groups such
as coliforms, for example). Thus, these embodiments may provide for
the detection and differentiation of microorganisms. In some
implementations, these embodiments may provide for the confirmation
of a particular species, genus, or group of microorganisms. For
example, the first contrast layer may provide the observation of a
presumptive indication (e.g., CO.sub.2 production from the
metabolism of lactose by a coliform microorganism) of the presence
of a particular microorganism and the second contrast layer may
provide the observation of a confirmatory indication (e.g.,
hydrolysis of a chromogenic enzyme substrate for the
.beta.-galactosidase enzyme found in coliform microorganisms) of
the presence of the microorganism. In these embodiments, observing
an indication of growth comprises observing the growth area from an
observation position facing the first major surface of the culture
device.
[0085] In some embodiments of the method, observing an indication
of microbial growth further comprises detecting an observable
change in an indicator reagent (e.g., a pH indicator reagent or a
chromogenic or fluorogenic enzyme substrate). In these embodiments,
the indicator reagent may change to a derivative (e.g., a
protonated indicator reagent, a hydrolysed indicator reagent)
wherein the change in the indicator reagent (e.g., a color change
or fluorescence change) provides an observable bright spot, dark
spot, or color change in and/or adjacent the microbial colony 660.
Suitable indicator reagents include, for example fluorescent or
fluorogenic molecules and bioluminescent compounds.
[0086] In other embodiments of the method, observing an indication
of microbial growth comprises positioning an observer facing the
first major surface of a culture device and positioning a light
source facing the second major surface of the culture device, as
shown in FIG. 7.
[0087] The illustrated embodiment of FIG. 7 includes providing a
culture device 710 (shown in side view) configured to form a
highly-transmissible optical path extending from an outermost first
major surface 704 to an outermost second major surface 706. The
culture device 710 includes a base member 712, an optional adhesive
layer 714 coupled to the base member 712, a cover sheet 722, and a
gelling layer 716 disposed between the adhesive layer 714 and the
cover sheet 722. In the illustrated embodiment, the gelling layer
716 is hydrated with a liquid sample.
[0088] The culture device 10 is illuminated by photons from a light
source 770. The photons can generally pass through the
optically-transmissive culture device 710. A microorganism present
in the original sample can form a microbial colony 760 in the
gelling layer 716 of the culture device 710. Photons from the light
source 770 can strike the microbial colony 760 where they can be
reflected (shown as photon "A", which is reflected toward observer
790), transmitted, or absorbed, causing an observable bright spot,
dark spot or colored spot that contrasts with the brightness and/or
color of the components of the culture device 710 (e.g., the cover
layer, the gelling layer, the adhesive layer, and/or the base
member). In the illustrated embodiment, the light source 770 is
positioned facing the second major surface 706 of the culture
device 710. In the illustrated embodiment, observing an indication
of growth comprises observing the growth area from an observation
position (i.e., observer 790) facing the first major surface 704 of
the culture device 710.
[0089] In some embodiments of the method, observing an indication
of microbial growth further comprises providing an optical filter
(not shown) and positioning the optical filter between the light
source 770 and the culture device 710. In these embodiments, the
culture device 710 can be illuminated with selected wavelengths of
light (e.g., red wavelengths, blue wavelengths, ultraviolet
wavelengths). This configuration can be particularly advantageous
when the color of a microbial colony 760 is only slightly different
from the color of one or more components of the culture device
710.
[0090] In these embodiments (i.e., where the light source faces the
second major surface of the culture device, and the observer faces
the second major surface of the culture device, detecting the
presence or absence of a microorganism can comprise detecting the
scattering, absorbance or transmittance of light by a colony of
microorganisms and/or by an indicator reagent.
Detecting the Presence or Absence of a Microorganism by Observing
an Abiogenic Gas Bubble:
[0091] In another aspect, the present disclosure provides methods
for detecting the presence or absence of a microorganism by
observing the presence or size of an abiogenic gas bubble. The
methods comprise providing a sample and a culture device comprising
a base member, a cover layer, and a hydrogel disposed there
between. The hydrogel includes a plurality of abiogenic gas bubbles
distributed therein. The hydrogel defines a growth area in the
culture device. The methods further comprise inoculating the growth
area of the device with the sample, incubating the device for a
period of time, illuminating the culture device with a light
source, and detecting the presence or absence of a microorganism in
the culture device by detecting the diminution or absence of at
least one abiogenic gas bubble in the culture device at a first
point in time. These methods advantageously can be used to detect
the presence of a microbial colony before the colony can be
detected by other means (e.g., by visual detection of the colony,
by detecting a change in the optical properties of an indicator
(e.g., a chromogenic enzyme substrate a fluorogenic enzyme
substrate, a Ph indicator, a redox indicator) wherein the change is
associated with the presence of the microbial colony).
[0092] In some embodiments, the growth area of the culture device
comprises at least one nutrient to support the growth of a
microorganism. The growth area of the culture device may further
comprise at least one selective agent to select for the growth of a
particular microorganism or group of microorganisms (e.g.,
antibiotic-resistant microorganisms). The nutrients and/or
selective agents to favor the growth of a particular organism or
group of organisms (e.g., aerobic bacteria) are known to a person
of ordinary skill in the art. The nutrient or selective agent
should be selected such that it does not substantially interfere
with the formation and/or observation of abiogenic gas bubbles in
the hydrogel.
[0093] In some embodiments, the hydrogel is in uniform contact with
the base member and cover layer of the culture device throughout
the growth area of the device (i.e., the hydrogel is "sandwiched"
between the base member and the cover layer). In some embodiments,
the culture device can be a thin film culture device such as the
devices disclosed in U.S. Pat. No. 4,565,783. In some embodiments,
the culture device can be a highly optically-transmissive culture
device according to the present disclosure.
[0094] The abiogenic gas bubbles can be formed in the device
spontaneously when the device is hydrated with an aqueous liquid or
inoculated with a liquid sample (e.g., an aqueous liquid sample).
Without being bound by theory, abiogenic gas bubbles can be formed
when a dry, cold-water soluble gelling agent is hydrated with an
aqueous sample, causing air bubbles to become entrapped in the
hydrogel as the gelling agent swells. It may take about several
minutes to about several hours for the abiogenic gas bubbles to
become observable in the culture device after the device is
hydrated or inoculated. The abiogenic gas bubbles may be regularly
distributed or randomly distributed throughout the growth area of
the culture device. Preferably, the abiogenic gas bubbles are
uniformly distributed throughout the growth area of the culture
device. In certain preferred embodiments, the abiogenic gas bubbles
are approximately uniform in size. In some embodiments, the
abiogenic gas bubbles are less than about 1 mm in diameter. In
certain preferred embodiments, the abiogenic gas bubbles are about
0.5 mm to about 1.0 mm in diameter. In some embodiments, the
abiogenic gas bubbles are less than about 0.5 mm in diameter. In
general, smaller, uniformly distributed abiogenic gas bubbles can
permit greater sensitivity and resolution of the detection of
separate colonies of microorganisms in the culture device.
[0095] The number and spatial distribution of abiogenic gas bubbles
can facilitate the detection of a microorganism in the culture
device. Preferably, there are about 50-100 abiogenic gas bubbles
per square centimeter of hydrogel. More preferably, there are about
100 to about 500 abiogenic gas bubbles per square centimeter of
hydrogel. In some embodiments, there are about 200 abiogenic gas
bubbles per square centimeter.
[0096] The growth area of the culture device is inoculated with a
sample. In some embodiments, the hydrogel is formed by hydrating a
gelling agent (e.g., a cold water-soluble gelling agent) with an
aqueous liquid (e.g., sterile water, sterile buffer). In these
embodiments, the culture device can be opened (e.g., by lifting the
cover layer) to expose at least a portion of the hydrogel and the
hydrogel can be contacted with a sample. For example, a sample
collection device (e.g., a swab) can be contacted with the hydrogel
to transfer a solid or liquid sample to the culture device. In
alternative embodiments, a liquid sample can be pipetted onto the
hydrogel. In further alternative embodiments, the hydrogel can be
brought into contact with a surface (e.g., equipment, a floor, a
wall) to inoculate the hydrogel with material that was present on
the surface (e.g., dirt, dust, residues). After inoculation of the
hydrogel, the culture device is closed.
[0097] In the embodiments where the culture device comprises a dry,
rehydratable cold water-soluble gelling agent, the hydrogel can be
formed by contacting the dry gelling agent with a predetermined
volume (e.g., about 1 mL, about 5 mL) of aqueous liquid comprising
the sample.
[0098] In some embodiments, the culture device can comprise a
nutrient to support the growth of a microorganism, as described
above. Alternatively or additionally, a nutrient to support the
growth of a microorganism is provided in the liquid sample (e.g.,
the liquid sample is mixed with a nutrient prior to inoculating the
device with the liquid sample). After inoculation, the culture
device can be incubated for a period of time, as described
herein.
[0099] After inoculation, and before substantial microbial growth
has occurred in the culture device (e.g., less than the time it
takes about 1-2 cell divisions to occur), the culture device may be
observed or imaged to compare with the same culture device after
substantial microbial growth has occurred. Alternatively, a similar
culture device can be inoculated with a sterile liquid as a
control.
[0100] After incubation, the culture device can be observed for an
indication of the presence or absence of a microorganism. The
presence of a microorganism can be indicated by a discontinuity of
a plurality of abiogenic gas bubbles in the culture device at a
first point in time. That is, the culture device can be observed
for the presence of a plurality of abiogenic gas bubbles
distributed in the growth area. A discontinuity can be observed
when, within a region of the growth area, one or more of the
abiogenic gas bubbles are substantially smaller than the typical
abiogenic gas bubbles in the growth area and/or there is an area in
which one or more abiogenic gas bubbles are absent. Without being
bound by theory, the abiogenic gas bubbles may diminish in size or
disappear by the metabolism of gasses (oxygen, carbon dioxide,
and/or nitrogen) by a microorganism or by the microbial production
of surfactants that disperse one or more abiogenic gas bubbles. In
some embodiments, the presence of a discontinuity of abiogenic gas
bubbles in the culture device can be more apparent when the culture
device is observed (or imaged) at two or more time points (e.g.,
before substantial microbial growth has occurred and after
microbial growth has occurred) and the observations at each point
in time are compared.
[0101] Turning to the drawings, FIG. 3 shows a top view of one
embodiment of a culture device at a first point in time. The
culture device comprises abiogenic bubbles. The culture device 310
illustrated in FIG. 3 represents a culture device 310 after which
the abiogenic gas bubbles 340 have formed in the device but before
substantial microbial growth has occurred (e.g., within about 1 to
about 15 minutes after inoculation. The culture device 310 includes
a circular growth area 326 bounded by a spacer 318 containing
abiogenic gas bubbles 340 in a hydrogel 317. The gas bubbles 340
are randomly distributed throughout the growth area 326.
[0102] FIG. 4a shows a top view of the culture device of FIG. 3 at
a second point in time (e.g., about eight hours after inoculation).
FIG. 4b shows an enlargement of a portion of the culture device 410
of FIG. 4a. The enlargement shows a plurality of abiogenic gas
bubbles 440, as well as a plurality of diminished abiogenic gas
bubbles 442 distributed in the hydrogel 417. The diminished gas
bubbles 442 are observably smaller than the typical abiogenic gas
bubbles 440 in the growth area. It will be appreciated that the
discontinuity of the abiogenic gas bubbles in the culture device
410 can indicate the presence of a microorganism even though there
are no other visible indications of a microorganism colony at this
point in time.
[0103] FIG. 5a shows a top view of the culture device of FIG. 3 at
a third point in time (e.g., about twelve hours after inoculation).
FIG. 5b shows an enlargement of a portion of the culture device 510
of FIG. 5a. The enlargement shows a plurality of abiogenic gas
bubbles 540 and a plurality of observably-small abiogenic gas
bubbles 542 distributed in the hydrogel 517. FIG. 5b also shows an
observably bubble-free zone 544. The abiogenic gas bubbles 540,
observably-small abiogenic gas bubbles 542 and bubble-free zone 544
are all proximate a visible microbial colony 560. The observably
small abiogenic gas bubbles 542 are distinguishable from the
abiogenic gas bubbles 540 in that they are markedly smaller than
the normal size range of abiogenic gas bubbles 542 distributed
throughout the hydrogel 517.
[0104] In some embodiments of the methods, comparing observations
of the culture device at two or more time points can confirm the
development (e.g., due to the presence of a microorganism) of a
discontinuity in the size or presence of abiogenic gas bubbles in
the culture device.
[0105] In some embodiments of the methods, the culture device is
illuminated with ambient light (e.g., sunlight). In some
embodiments, the culture device is illuminated with a light source
that emits selected wavelengths of light (e.g., white light,
ultraviolet light).
[0106] In some embodiments, illuminating the culture device
comprises illuminating the culture device with a light source
positioned facing an outermost first major surface or second major
surface of the culture device, as described above. In some
embodiments, the observing an indication of growth comprises
observing an indication of growth with the observer facing the
first major surface or second major surface of the culture device,
as described above.
[0107] In some embodiments, observing an indication of growth
further comprises positioning a contrast layer on the major surface
of the culture device opposite the major surface that the observer
(e.g., the operator or an imaging device) is facing. In any of the
embodiments, detecting the presence or absence of a microorganism
can comprise detecting the scattering, absorbance or transmittance
of light (e.g., scattering, absorbance, or transmittance of light
by a microbial colony). In any of the above embodiments, detecting
the presence or absence of a microorganism can comprise enumerating
microorganisms.
Detection of an Indication of Microbial Growth Using an Imaging
System:
[0108] In any of the above embodiments, the method further can
comprise providing an imaging system and obtaining an image of the
culture device. In these embodiments, detecting the presence or
absence of a microorganism comprises displaying, printing, or
analyzing the image of the culture device. The imaging system
comprises an imaging device and may comprise a processor. In some
embodiments, the imaging device can comprise a line-scanner or an
area scanner (e.g., a camera). The imaging device can include a
monochromatic (e.g., black-and-white) or a polychromatic (e.g.,
color) scanner. Advantageously, monochromatic imaging systems can
provide higher resolution images, which may improve the accuracy of
the result and/or reduce the time necessary to detect the presence
of microorganisms in the culture device.
[0109] In some embodiments, the imaging system further comprises an
illumination system. The illumination system may include at least
one source of broad-spectrum visible light (e.g., a "white" light).
In some embodiments, the illumination system may include at least
one source of narrow-spectrum visible light (e.g., a light-emitting
diode that emits a relatively narrow bandwidth of visible light
such as, for example, red, green, or blue light). In certain
embodiments, the illumination system may include a source of
narrow-spectrum visible light (e.g., a light-emitting diode) with a
light emission peak at about 525 nm.
[0110] The image can be obtained from light reflected by the
hydrogel in the culture device or the image can be obtained from
light transmitted through the hydrogel in the culture device.
Suitable imaging systems and corresponding illumination systems are
described, for example, in International Patent Publication No. WO
2005/024047 and U.S. Patent Application Publication Nos. US
2004/0101954 and US 2004/0102903, each of which is incorporated
herein by reference in its entirety. Non-limiting examples of
suitable imaging systems include PETRIFILM Plate Reader (PPR),
available from 3M Company (St. Paul, Minn.), the PETRISCAN Colony
Counter available from Spiral Biotech (Norwood, Mass.), and
PROTOCOL and ACOLYTE plate scanners available from Synbiosis
(Cambridge, U.K.)
[0111] In some embodiments, obtaining an image comprises obtaining
a wavelength-biased image. For example, the imaging system can
include a bias filter that biases the light collected by the
imaging device. Filter elements are known in the art and include
both "cut-off" filters (i.e., filters that allow the passage of
light wavelengths either above or below a certain specified
wavelength) and "band-pass" filters (i.e., filters that allow the
passage of light wavelengths between certain specified upper and
lower limits) A bias filter can be positioned between the
illumination source and the culture device. Alternatively or
additionally, a bias filter can be positioned between the culture
device and the imaging device.
[0112] In certain preferred embodiments, obtaining an image
comprises obtaining an image using a bias filter that selectively
allows the passage of red wavelengths. In some embodiments,
obtaining an image comprises using a bias filter that selectively
allows the passage of wavelengths from about 500 nm to about 550
nm.
[0113] FIG. 8 is a block diagram illustrating internal operation of
an imaging system 870. As illustrated in FIG. 8, a culture device
882 is positioned in a focal plane (e.g., on a platform, not shown)
within imaging system. In accordance with the invention, imaging
device 892 may include multi-color illumination systems (not shown)
for front and/or back illumination of culture device 882, as well
as a monochromatic line or area scanner that captures an image of
the culture device 882. In some embodiments, for example, imaging
device 892 may take the form of a two-dimensional, monochromatic
camera.
[0114] In general, imaging device 892 captures images of culture
device 882, or at least a portion thereof, during illumination of
the culture device with one or more different illumination colors.
In some embodiments, multiple images of the same culture device 882
can be generated with various illumination durations or intensities
and one or more of the multiple images can be selected for
analysis. In some embodiments, selective illumination of a first
side and a second side of the culture device 882 can be used to
generate multiple images of the culture device and one or more of
the images can be selected for analysis. Selection of an image for
analysis can be based on, for example, the color contrast and/or
object resolution properties of the individual images. Processes
for determining the color contrast and object resolution properties
of an image are known in the art and are disclosed in, for example,
U.S. Pat. No. 6,243,286, which is incorporated herein by reference
in its entirety.
[0115] A processor 894 controls the operation of imaging device
892. Also shown in FIG. 8 is optional display 876, which can
receive an image from the processor 894 for visual review by an
operator. In operation, processor 894 controls imaging device 892
to illuminate the culture device 882 and obtain an image. Processor
894 receives image data representing the scanned image from imaging
device 892. In some embodiments, processor 894 can select an image,
from multiple images, for analysis and/or display. Processor 894
analyzes at least one image of culture device 882 and may produce
an analytical result, such as a count of colonies of microorganisms
or a determination of the presence or absence of microorganisms in
a sample. The analytical result (e.g., a qualitative or
quantitative result) can be displayed on display 876, stored in
optional data storage memory 898, or retrieved by a host computer
(not shown) via optional communication port 895
[0116] Analyzing the image of the culture device can comprise using
a system to detect color and/or varying shades of a color (e.g.,
red, green, blue, gray) in an image. Suitable image analysis
systems include the image analysis systems described in, for
example, U.S. Pat. Nos. 5,448,652; 6,243,486; and 6,153,400; each
of which is incorporated herein by reference in its entirety.
[0117] In certain embodiments, analyzing the image of the culture
device comprises analyzing selected wavelengths of the image. In
some embodiments, the image may be a color image collected by
illuminating the culture device with a source of broad-spectrum
visible light (e.g., a "white" light). In some embodiments, the
image may be a color image collected by illuminating the culture
device with a plurality of sources of relatively narrow-spectrum
visible light (e.g., a combination of light-emitting diodes that
each emits a relatively narrow bandwidth of visible light such as,
for example, red, green, or blue light). In some embodiments, the
image may be a composite image made by combining two or more images
collected while illuminating the culture device with two or more
different sources of relatively narrow-spectrum visible light
(e.g., red, green, or blue light). In some embodiments, the image
may be an image collected while illuminating the culture device
with a source of relatively narrow-spectrum visible light (e.g.,
green light). In these embodiments, certain wavelengths of the
image can be selected for displaying or printing an image and/or
image analysis.
[0118] In some embodiments (e.g., wherein the color of the pH
indicator ranges from red to yellow), the wavelengths selected for
analyzing the image can be wavelengths in the green color range
(e.g., wavelengths about 500 nm to about 550 nm). In some
embodiments, the wavelengths selected for analysis are wavelengths
about 520 nm to about 530 nm. In some embodiments, the wavelength
selected for analysis is about 525 nm.
[0119] The wavelengths can be selected, for example, by using a
computer program that electronically selects a predetermined range
of wavelengths in the image for display, printing, and/or analysis.
For example, a predetermined green wavelength or range of green
wavelengths may be particularly suitable to display, print, or
analyze an image of a yellow-colored zone adjacent a colony of
microorganisms growing in a red-colored culture medium (e.g., a
culture medium comprising chlorophenol red). Any suitable computer
program can be used to select a predetermined range of wavelengths
in an image. Non-limiting examples of suitable computer programs
include PHOTOSHOP CS4 software, available from Adobe Systems, Inc.
(San Jose, Calif.) and IMAGE-PRO Plus software, available from
Media Cybernetics (Silver Springs, Md.).
[0120] In certain embodiments, wherein the image of the culture
device has been obtained and/or analyzed in a manner that biases
the collection in the image of green wavelengths either transmitted
through and/or reflected by the hydrogel in the culture device, the
contrast between the pH indicator (e.g., the red-colored
chlorophenol red) in the culture medium and the acid zone (e.g.,
the yellow-colored chlorophenol red) adjacent the bacterial
colonies is significantly enhanced. Thus, in these embodiments,
lactic acid bacteria are detectable at an earlier time than in
comparable methods that do not bias the wavelengths of the image
that is collected.
EMBODIMENTS
[0121] Embodiment 1 is a method for detecting the presence or
absence of a microorganism in a sample, comprising:
[0122] providing a liquid sample and a culture device comprising a
base member, a cover layer, and a dry cold water-soluble gelling
agent disposed on the base member and/or cover layer; [0123]
wherein the culture device includes an outermost first major
surface, an outermost second major surface, and a growth area;
[0124] wherein the culture device is configured to form a highly
transmissive optical path extending from the first major surface to
the second major surface;
[0125] hydrating the growth area of the device with the sample;
[0126] incubating the device for a period of time; and
[0127] illuminating the growth area with a light source, and
[0128] detecting the presence or absence of a microorganism in the
growth area;
[0129] wherein detecting the presence or absence of a microorganism
comprises observing an indication of growth.
[0130] Embodiment 2 is the method of embodiment 1, wherein the
culture device further comprises an adhesive layer coupled to the
base member and/or the cover sheet, wherein the gelling agent is
disposed on the adhesive layer.
[0131] Embodiment 3 is the method according to embodiment 1 or
embodiment 2, wherein illuminating the growth area comprises
illuminating the growth area with the light source positioned
facing the first major surface of the culture device.
[0132] Embodiment 4 is the method according to any one of the
preceding embodiments, wherein observing an indication of growth
comprises observing the growth area from an observation position
facing the first major surface of the culture device.
[0133] Embodiment 5 is the method according to embodiment 1 or
embodiment 2, wherein illuminating the growth area comprises
illuminating the growth area with the light source positioned
facing the second major surface of the culture device.
[0134] Embodiment 6 is the method according to embodiment 5,
wherein observing an indication of growth comprises observing the
growth area from a position facing the first major surface of the
culture device.
[0135] Embodiment 7 is the method of any one of embodiments 1
through 4 wherein, overlapping at least a portion of the growth
area of the culture device, the second major surface of the culture
device comprises a contrast layer.
[0136] Embodiment 8 is the method of embodiment 4, further
comprising:
[0137] providing a first contrast layer; and
[0138] prior to detecting the presence or absence of a
microorganism, positioning the first contrast layer proximate the
second major surface of the culture device.
[0139] Embodiment 9 is the method of embodiment 8, further
comprising:
[0140] providing a second contrast layer; and prior to detecting
the presence or absence of a microorganism, positioning the second
contrast layer proximate the second major surface of the culture
device.
[0141] Embodiment 10 is the method of any one of embodiments 7
through 9, wherein at least one contrast layer substantially
reflects the light.
[0142] Embodiment 11 is the method of any one of embodiments 7
through 9, wherein at least one contrast layer is a specularly
reflective layer
[0143] Embodiment 12 is the method of any one of embodiments 7
through 9, wherein at least one contrast layer substantially
absorbs selected wavelengths of light.
[0144] Embodiment 13 is the method of any one of embodiments 1
through 3, wherein observing an indication of growth comprises
observing the growth area from a position facing the second major
surface of the culture device.
[0145] Embodiment 14 is the method of any one of the preceding
embodiments, wherein detecting the presence or absence of a
microorganism comprises detecting the scattering, absorbance or
transmittance of light.
[0146] Embodiment 15 is the method of embodiment 14, wherein
detecting the presence or absence of a microorganism comprises
detecting the scattering, absorbance or transmittance of light by a
colony of microorganisms.
[0147] Embodiment 16 is the method of any one of the preceding
embodiments, further comprising adding an indicator reagent, and
wherein detecting the presence or absence of a microorganism
comprises detecting an observable change in the indicator
reagent.
[0148] Embodiment 17 is the method of any one of the preceding
embodiments, wherein detecting the presence or absence of a
microorganism comprises detecting a fluorescent signal.
[0149] Embodiment 18 is a method for detecting the presence or
absence of a microorganism in a sample, comprising:
[0150] providing a sample and a culture device comprising a base
member, a cover layer, and a hydrogel comprising a plurality of
abiogenic gas bubbles disposed there between; [0151] wherein the
culture device comprises an outermost first major surface and an
outermost second major surface; [0152] wherein the hydrogel defines
a growth area;
[0153] inoculating the growth area of the device with the sample at
a first point in time;
[0154] incubating the device for a period of time;
[0155] illuminating the growth area with a light source; and
[0156] detecting the presence or absence of a microorganism in the
growth area at a second point in time;
[0157] wherein detecting the presence or absence of a microorganism
comprises observing an indication of growth;
[0158] wherein observing an indication of growth comprises
detecting the diminution or absence of at least one abiogenic gas
bubble in the hydrogel at the second point in time.
[0159] Embodiment 19 is the method of embodiment 18; wherein
providing the culture device comprises providing a thin film
culture device that includes a dry, cold water-soluble gelling
agent and wherein the method further comprises hydrating the
gelling agent with an aqueous liquid.
[0160] Embodiment 20 is the method of embodiment 19, wherein the
aqueous liquid comprises the sample.
[0161] Embodiment 21 is the method of embodiment 19 or embodiment
20, wherein the device is substantially optically transmissible
when the gelling agent is hydrated with a clear aqueous liquid.
[0162] Embodiment 22 is the method of any one of embodiments 18
through 21, further comprising:
[0163] observing the growth area with regard to the size or absence
of the gas bubble at a third point in time, wherein the third point
in time occurs after the second point in time; and
[0164] comparing observations of the growth area at two points in
time.
[0165] Embodiment 23 is the method of any one of embodiments 18
through 22, wherein illuminating the growth area comprises
illuminating the growth area with the light source positioned
facing the first major surface of the culture device.
[0166] Embodiment 24 is the method of any one of embodiments 18
through 23, wherein observing an indication of growth comprises
observing the growth area from an observation position facing the
first major surface of the culture device.
[0167] Embodiment 25 is the method of any one of embodiments 18
through 22, wherein illuminating the growth area comprises
illuminating the growth area with the light source positioned
facing the second major surface of the culture device.
[0168] Embodiment 26 is the method according to embodiment 23,
wherein observing an indication of growth comprises observing the
growth area from a position facing the first major surface of the
culture device.
[0169] Embodiment 27 is the method of any one of embodiments 18
through 22 wherein, overlapping at least a portion of the growth
area of the culture device, the second major surface of the culture
device comprises a contrast layer.
[0170] Embodiment 28 is the method of embodiment 22, further
comprising:
[0171] providing a first contrast layer; and
[0172] prior detecting the presence or absence of a microorganism,
positioning the first contrast layer proximate the second major
surface of the culture device.
[0173] Embodiment 29 is the method of embodiment 28, further
comprising:
[0174] providing a second contrast layer; and
[0175] prior detecting the presence or absence of a microorganism,
positioning the second contrast layer proximate the second major
surface of the culture device.
[0176] Embodiment 30 is the method of any one of embodiments 27
through 29, wherein at least one contrast layer substantially
reflects the light.
[0177] Embodiment 31 is the method of any one of embodiments 27
through 29, wherein at least one contrast layer is a specularly
reflective layer
[0178] Embodiment 32 is the method of any one of embodiments 27
through 29, wherein at least one contrast layer substantially
absorbs selected wavelengths of light.
[0179] Embodiment 33 is the method of any one of embodiments 27
through 29, wherein observing an indication of growth comprises
observing the growth area from a position facing the second major
surface of the culture device.
[0180] Embodiment 34 is the method of any one of the preceding
embodiments, wherein detecting the presence or absence of a
microorganism comprises detecting the scattering, absorbance or
transmittance of light.
[0181] Embodiment 35 is the method of embodiment 32, wherein
detecting the presence or absence of a microorganism comprises
detecting the scattering, absorbance or transmittance of light by a
colony of microorganisms.
[0182] Embodiment 36 is the method of any one of the preceding
embodiments, wherein detecting the presence or absence of a
microorganism comprises enumerating microorganisms.
[0183] Embodiment 37 is the method of any one of the preceding
embodiments, wherein detecting the presence or absence of a
microorganism comprises detecting and differentiating two or more
types of microorganisms.
[0184] Embodiment 38 is the method of any one of the preceding
embodiments, wherein detecting the presence or absence of a
microorganism further comprises:
[0185] providing an imaging system; and
[0186] obtaining an image of the growth area of the culture
device;
[0187] wherein observing an indication of growth comprises
displaying, printing, or analyzing the image of the growth
area.
[0188] Embodiment 39 is a device for detecting microorganisms,
comprising:
[0189] a base member;
[0190] a cover layer;
[0191] a cold water soluble gelling agent disposed on the adhesive
layer
[0192] wherein the device is substantially optically transmissible
when the gelling agent is hydrated with a clear aqueous liquid.
[0193] Embodiment 40 is the device of embodiment 39, further
comprising a first adhesive layer coupled to one of the base member
or the cover layer.
[0194] Embodiment 41 is the device of embodiment 40, further
comprising a second adhesive layer coupled to the other of the base
member or cover layer.
[0195] Embodiment 42 is the device of embodiment 41, further
comprising a nutrient medium disposed on the first or second
adhesive layer.
[0196] Embodiment 43 is the device of any one of embodiments 40
through 42, further comprising an indicator reagent.
[0197] Embodiment 44 is the device of any one of embodiments 40
through 43, further comprising an optical filter layer or a
contrast layer.
[0198] Embodiment 45 is the device of any one of embodiments 40
through 44, wherein the optical haze of the culture device after
hydration of the device with a clear aqueous liquid is .ltoreq.95%
when measured according to ASTM 1003.
[0199] Embodiment 46 is the device of any one of embodiments 40
through 45, wherein the optical clarity of the culture device after
hydration of the device with a clear aqueous liquid is .gtoreq.10%
when measured according to ASTM 1003.
[0200] The invention will be further illustrated by reference to
the following non-limiting Examples. All parts and percentages are
expressed as parts by weight unless otherwise indicated.
EXAMPLES
Example 1
Preparation of a Thin Film Culture Device for Yeast and Mold
Detection
[0201] A pressure-sensitive adhesive coated polyolefin film having
a silicone pressure-sensitive adhesive (3M.TM. Advanced Polyolefin
Diagnostic Tape Catalog #9795R available from 3M Company, St. Paul,
Minn.) was used to prepare a powder coated base member for a thin
film culture device. The tape had a 2-mil thick clear polyolefin
backing and a 2-mil thick layer of silicone pressure-sensitive
adhesive, and a white release liner.
[0202] A powder nutrient composition was prepared by thoroughly
mixing a powder containing 14.3% (all percentages are weight %)
pancreatic digest of casein, 25.5% meat peptone, 9.5% yeast
extract, 43.4% dextrose, 6% pepticase, 1% ferric ammonium citrate,
0.3% calcium chloride, and sufficient sodium carbonate to adjust
the pH to about 7. A gelling powder composition was prepared by
mixing in a 1:1 weight ratio xanthan gum powder and locust bean gum
powder (both available from Spectrum Chemical Mfg. Corp (Gardena,
Calif.)). Sufficient silica (Cab-O-Sil M5 available from Cabot
Corp. (Bilerica, Mass.) was added to enhance flow and prevent
clumping. The amount is less than about 0.5 weight %. The nutrient
composition was mixed with the gelling powder composition in a 1:4
weight ratio. A base member was prepared by sprinkling an excess of
the mixed powder composition onto the adhesive coated side of the
tape. Excess powder was removed by tilting the sheet and tapping
lightly by hand.
[0203] A powder gelling composition was prepared by mixing 500
grams of xanthan gum powder (NF Grade Xanthan Gum, obtained from
Spectrum Chemical Manufacturing Corp., Gardena, Calif.) and 500
grams of locust bean gum (FCC Grade Locust Bean gum obtained from
Spectrum Chemical Manufacturing Corp., Gardena, Calif.) with about
2.9 grams of silica (Cab-O-Sil M5). A cover sheet was prepared by
sprinkling the powder composition onto a clear adhesive coated tape
(3M.TM. Advanced Polyolefin Diagnostic Tape Catalog #9795R) and
removing the excess powder by tilting the sheet and tapping lightly
by hand.
[0204] Rectangular plate devices measuring 3 inches by 3.75 inches
were cut from the coated sheet to form a base member, and from the
coated film to form a cover film. A thin film culture device was
assembled by adhering a strip of double coated pressure-sensitive
adhesive tape on one end the coated base plate and adhering one end
of the cover sheet to it so that the coated surfaces faced each
other and the tape functioned as a hinge to hold the cover sheet to
the base member FIG. 1.
Example 2
Preparation of a Thin Film Culture Plates for Aerobic Bacteria
Detection
[0205] A thin film culture device was prepared according to the
procedure of Example 1 except that the nutrient composition for the
base member was prepared by thoroughly mixing of 22.8 parts of
pancreatic digest of casein, 15.9 parts of yeast extract, 45.5
parts of sodium pyruvate, 4.1 parts of dextrose, 9.0 parts of
dibasic potassium phosphate, and 2.8 grams of monobasic potassium
phosphate. A powder gelling composition was prepared by mixing guar
gum (M150 guar MEYPROGAT gum, Meyhall Chemical AG) with a
sufficient amount of silica (Cab-O-Sil M5 silica) to prevent
clumping and enhance flow (less than about 0.5%)
[0206] A cover sheet was prepared according to the procedure of
Example 1 except that the powder gelling agent composition was
prepared by mixing xanthan gum powder (obtained from Spectrum
Chemical Mfg. Corp. (Gardena, Calif.)) locust bean gum powder
(obtained from Spectrum Chemical Mfg. Corp. (Gardena, Calif.)) in a
1:1 weight ratio with silica to prevent clumping.
Example 3
Testing of Thin Film Culture Devices for Yeast and Mold
[0207] A mold (filamentous fungus), Paecilomyces sp. (3M Culture
Designation M-10) was propagated by aseptically placing one
lyophilized pellet of the mold (obtained from Microbiologics (St.
Cloud, Minn.)) in 99 mL Butterfield's Phosphate Diluent (BPD
obtained from Edge Biologicals (Memphis, Tenn.)) in a bottle,
shaking the bottle, and allowing the mixture to stand at room
temperature (about 23.degree. C.) for 30 minutes. The suspension
was shaken again, and 2 mL was transferred to a second bottle
containing 99 mL of BPD and shaken. One milliliter of the second
suspension was inoculated onto a thin film culture device from
Example 1 and also onto a control device (3M PETRIFILM Yeast &
Mold Count Plate obtained from 3M Company (St. Paul, Minn.))
according to the manufacturer's instructions.
[0208] The inoculated devices were incubated simultaneously at
25.degree. C. using an incubation and imaging system as follows.
The system included an incubation system having platform coupled to
a temperature controller (product number TC-36-25-RS232 obtained
from TE Technology, Inc. (Traverse City, Mich.), an illumination
source (Leica KL2500LCD 3000 degrees K available from Leica
Microsystems GmbH (Wetzlar, Germany), coupled to two illumination
guides (Schott A08975 available from Schott North America, Inc.
(Southbridge, Mass.), and a camera (NIKON Coolpix 8400. The camera
was positioned about 14 inches above the platform to take images at
60 minute intervals during incubation of the thin film culture
devices. Two devices, positioned side-by-side on a shiny aluminum
plate on the heating platform, were incubated and imaged
simultaneously. The two illumination guides were positioned a about
a 45 degree angle to the platform and about 8 inches away on
opposing sides to direct light at an angle onto the top surface of
the devices. Alternatively, instead of an aluminum plate, a mirror
or a mirror film such as a Vikuiti.TM. Enhanced Specular Reflector
(available from 3M Company (St. Paul, Minn.)) may be used. A series
of fixed temporal (fixed 60 minute automatic acquisition interval)
images were taken of the plates during an incubation period of 56
hours. The images were of the device of Example 1 next to a control
device, both inoculated with the same culture.
[0209] The elapsed time for detection on the device of Example 1
was determined by observing the light scatter through the device
and noting the earliest time a change in scatter was detected, as
indicated by clearing zones FIGS. 4a and 4b. The elapsed time for
the control device was determined by observing the color change of
the indicator in the device at the earliest time the change was
detected. Observations from the images for Paecilomyces sp on the
devices of Example 1 and the control are shown in Table 2. The
observations note the visual changes of the images at the time
elapsed since inoculation. The earliest time at which the visual
perception threshold is reached for identifying a colony forming
unit (CFU) is noted as well as continuing changes throughout the
incubation period. The elapsed time for the earliest detection for
all of the plates is summarized in Table 3.
[0210] A yeast, Saccharomyces cerevisiae, (obtained from
Microbiologic (St. Cloud, Minn.) was tested on a device from
Example 1 using the same preparation method described above and
tested with a control. Results are summarized in Table 3.
TABLE-US-00002 TABLE 2 Elapsed time observations of Paecilomyces sp
Time Observations Elapsed Example 1 Control 32 hours No observable
change; uniform field No observable of small bubbles on plate -
FIG. 3 change 34 hours Mold is at the CFU visual perception No
observable threshold - FIGS. 4a and 4b change 36 hours CFU
morphology taking form; local No observable bubbles start to
diminish in size - FIGS. change 5a and 5b 56 hours Mold CFU
morphology sharply CFU at visual defined and much larger than the
perception indicator region of the control plate; threshold of
bubbles reducing in size, then clearing - blue-green color FIGS. 5
and 5B of indicator. 76 hours* 1 colony seen on plate; colony
larger 4 colonies visible than indicator regions on control plate
*The inoculum population was intentionally kept low so the number
of colonies was not considered a significant event in this
test.
TABLE-US-00003 TABLE 3 Earliest elapsed time to detection on yeast
and mold plates Elapsed Time Elapsed Time Organism Example 1
Control Time difference Paecilomyces sp 33 hours 55 hours 23 hours
(42%) Saccharomyces 23 hours 45 hours 22 hours (49%) cerevisiae
Example 4
Testing of Thin Film Culture Devices for Aerobic Bacteria
[0211] The control plates used were 3M PETRIFILM Aerobic Count
plates, obtained from 3M Company (St. Paul, Minn.).
[0212] Two bacterial organisms obtained from the American Type
Culture Collection (Manasses, Va.) were used to evaluate the
culture device of Example 1 and a control. The organisms were
Escherichia coli (ATCC 51813) and Staphylococcus aureus (ATCC
25923).
[0213] Bacterial cultures were prepared by inoculating pure
cultures into tryptic soy broth (TSB available from Remel (Lenexa
Kans.) and incubated at 35.degree. C. for 21 hours, static. One
loop (about 5 microliters) was transferred into fresh TSB and
incubated at 35.degree. C. for 21 hours, static. In the primary
dilution, 10 microliters of the vortexed culture pipetted into 99
mL of Butterfield's Phosphate Diluent (BPD available from Edge
Biologicals (Memphis Tenn.)) in a sample bottle and shaken to mix.
In the secondary dilution, 30 microliters from the primary dilution
was added to 99 mL of BPD and shaken to mix. One milliliter of the
secondary dilution, containing about 10 colony forming units
(CFUs), was used to inoculate a 3M PETRIFILM Aerobic Count plate
according to the manufacturer's instructions. One milliliter was
used to inoculate devices of Example 1 in the same manner.
Inoculated plates were incubated at 35.degree. C. for 48 hours and
imaged using the system and method described in Example 3. Images
were taken at 30 minute intervals. The elapsed time for observing
the first CFUs is summarized in Table 4.
TABLE-US-00004 TABLE 4 Elapsed time observation of aerobic bacteria
plates Elapsed Time Elapsed Time Organism Example 1 Control Time
difference Escherichia coli 7.5 hours 16.5 hours 9 hours (55%)
Staphylococcus 8 hours 12.5 hours 4.5 hours (36%) aureus
Example 5
Use of a Contrast Layer to Enhance Detection
[0214] A culture device was prepared according to the method of
Example 2 and tested according to the method of Example 4 using
Escherichia coli (ATCC 51813). A control device was also prepared
and tested. The culture devices were incubated at 35.degree. C. for
48 hours. The device of Example 2 with E. coli was placed on a
reflector (Vikuiti.TM. Enhanced Specular Reflector. The colonies
were noticeable more apparent to the naked eye when the device was
observed on the reflector. The reflector background made the CFU
morphology easier to see because of the enhanced contrast. There
was also better contrast between the bubble and bubble-free zones.
A white paper printed with yellow gridlines, used in the control,
was placed between the reflector and the bottom surface of the
culture device. The changes in morphology and bubble clearing were
less visible with the paper.
[0215] The cover film of the control was carefully lifted and a
piece of the Vikuiti.TM. Enhanced Specular Reflector was inserted
so that it covered about 1/3 of the inoculated zone. Red colonies
from the indicator were quite visible on the bubbles with the
reflector inserted. The reflector enhanced the visibility of the
bubble clearing zones.
Example 6
Thin Film Culture Device with Modified Guar Gum
[0216] A thin film culture device was prepared according to the
method of Example 2 except that the gum used was a modified guar
powder (Jaguar C162 obtained from Rhodia).
Example 7
Haze, Clarity, and Transmittance Properties of Films and Culture
Devices
[0217] Thin film culture devices and constituent parts were
measured for optical properties--light transmittance, haze, and
clarity. The % haze is an indication of the amount of light
scattering and is an indication of how easy it is to observe
changes in the CFU morphology during incubation. Measurements for
haze, clarity and transmittance were measured in the transmission
mode according to the manufacturer's instructions and in
conformance to ASTM 1003 using a light measuring instrument (BYK
Gardner Haze-gard plus, Catalog #4725, Serial #102485 available
from BYK-Gardner USA (Columbia, Md.). A baseline for the instrument
was established without a device under test, i.e., the tape or the
thin film culture device, etc. in the sample path and results were
0% haze, 100% clarity, and 100% transmission as expected.
[0218] Optical properties are shown in Table 9. Each point on the
graph represents an average of 4 or 5 readings. Sample 1 was a dry
powder coated cover sheet from a 3M PETRIFILM Aerobic Count plate
(AC plate) tested with the powder side facing the light detector
sphere. Sample 2 was two cover sheets from AC plates inoculated
with a buffer. Sample 3 was a biaxially oriented polypropylene
(BOPP) film without adhesive from an AC plate. Sample 4 was the
BOPP film with the adhesive from an AC Plate. Sample 5 was 3M.TM.
Advanced Polyolefin Diagnostic Tape Catalog #9795R. Sample 6 was
the base member coupled with the cover sheet from Example 2 and
inoculated with liquid diluent. Sample 7 was the device of Example
6 inoculated with a liquid diluent.
[0219] Sample 5, without the liner had an average light
transmittance of 94.5%, haze of 8.8%, and clarity of 95.8%. Sample
6, the thin film culture device after inoculation had a light
transmittance of 91.9%, haze of 34.7%, and clarity of 66%.
Example 8
Sterilization of Ingredients
[0220] The powders for the cover sheets of Examples 1 and 2 are
sterilized by treatment with ethylene oxide gas and then aerated to
remove any residual ethylene oxide gas prior to coating.
Example 9
Sterilization of Thin Film Culture Devices
[0221] Thin film culture devices of Examples 1 and 2 are placed in
an ethylene oxide atmosphere in an enclosed chamber and
sterilized.
[0222] The present invention has now been described with reference
to several specific embodiments foreseen by the inventor for which
enabling descriptions are available. Insubstantial modifications of
the invention, including modifications not presently foreseen, may
nonetheless constitute equivalents thereto. Thus, the scope of the
present invention should not be limited by the details and
structures described herein, but rather solely by the following
claims, and equivalents thereto.
* * * * *