U.S. patent application number 09/912266 was filed with the patent office on 2002-05-09 for method and apparatus for viable and nonviable prokaryotic and eukaryotic cell quantitation.
Invention is credited to Fleming, James E., Holcomb, Jerad R., McLean, Darby, Somes, Jason Buck.
Application Number | 20020055134 09/912266 |
Document ID | / |
Family ID | 22822980 |
Filed Date | 2002-05-09 |
United States Patent
Application |
20020055134 |
Kind Code |
A1 |
Fleming, James E. ; et
al. |
May 9, 2002 |
Method and apparatus for viable and nonviable prokaryotic and
eukaryotic cell quantitation
Abstract
A rapid method for the quantitation of various live cell types
is described. The method may include a variety of steps including:
1) suspending the cells in a detergent-like compound, 2) isolating
the washed cells by centrifugation or filtration, 3) resuspending
the cells in a solution that contains a preservative, a fluorescent
dye and a compound such as dequalinium which can be taken up by the
cells, 4) measuring the fluorescence increase over time of the
cell-dye mixture with a simple fluorometer, and 5) measuring the
native fluorescence of the cells. This new cell fluorescence method
correlates with other methods of enumerating cells such as the
standard plate count, the methylene blue method and the slide
viability technique. The method is particularly usefull in several
applications such as: a) quantitating bacteria in milk, yogurt,
cheese, meat and other foods, b) quantitating yeast cells in
brewing, fermentation and bread making, c) quantitating mammalian
cells in research, food and clinical settings. The method is
especially useful when both total and viable cell counts are
required such as in the brewing industry. The method can also be
employed to determine the metabolic activity of cells in a sample.
The apparatus, device, and/or system used for cell quantitation is
also disclosed.
Inventors: |
Fleming, James E.; (Spokane,
WA) ; Somes, Jason Buck; (Spokane, WA) ;
McLean, Darby; (Spokane, WA) ; Holcomb, Jerad R.;
(Spokane, WA) |
Correspondence
Address: |
SEED INTELLECTUAL PROPERTY LAW GROUP PLLC
701 FIFTH AVE
SUITE 6300
SEATTLE
WA
98104-7092
US
|
Family ID: |
22822980 |
Appl. No.: |
09/912266 |
Filed: |
July 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60220298 |
Jul 24, 2000 |
|
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|
Current U.S.
Class: |
435/32 ;
435/30 |
Current CPC
Class: |
C12Q 1/06 20130101; Y10T
436/101666 20150115 |
Class at
Publication: |
435/32 ;
435/30 |
International
Class: |
C12Q 001/24 |
Claims
1. A method for determining the percent viability of cells in a
sample, comprising providing a sample containing said cells,
detecting the total cell count, contacting said cells with molecule
or dye that is detectably altered by enzymatic activity of a viable
cell, detecting enzymatically altered dye or molecule, thereby
detecting the number of viable cells and comparing the number of
total cells with the number of viable cells thereby determining the
percent viability.
2. The method of claim 1, wherein said cells are bacteria.
3. The method of claim 1, wherein said cells are yeast.
4. The method of claim 1, wherein said total cell count is
determined by a method selected from the group consisting of native
UV absorption, turbidity testing, hemacytometer measurements,
fluorescence, and dye exclusion.
5. The method of claim 4, wherein said total cell count is
determined by UV absorption.
6. The method of claim 1, wherein the enzymatic activity is
esterase activity.
7. The method of claim 1, wherein said enzymatically altered dye or
molecule comprises fluorescein diacetate or OREGON GREEN.TM..
8. The method of claim 1, wherein detection is performed by a
flurorometer.
9. A method for detecting viable cells, comprising providing a
sample containing cells, contacting said sample with a dye that
diffuses or is transported into said cells and wherein said dye is
detectably altered by enzymatic activity of a viable cell, thereby
detecting viable cells in a sample.
10. The method of claim 9, wherein said cells are bacteria.
11. The method of claim 9, wherein said cells are yeast.
12. The method of claim 9, wherein said total cell count is
determined by a method selected from the group consisting of native
UV absorption, turbidity testing, hemacytometer measurements,
fluorescence, and dye exclusion.
13. The method of claim 12, wherein said total cell count is
determined by UV absorption.
14. The method of claim 9, wherein the enzymatic activity is
esterase activity.
15. The method of claim 9, wherein said enzymatically altered dye
or molecule comprises fluorescein diacetate or OREGON
GREEN.TM..
16. The method of claim 9, wherein detection is performed by a
flurorometer.
17. A method for quantitating viable cells in a sample, comprising
providing a sample containing said cells, contacting said cells
with molecule or dye that is detectably altered by enzymatic
activity of a viable cell, detecting ezymatically altered dye or
molecule, thereby detecting the number of viable cells in said
sample and obtaining a value therefrom and correlating the detected
viable cell value with a standard value, thereby quantitating the
viable cells in said sample.
18. The method of claim 17, wherein said cells are bacteria.
19. The method of claim 17, wherein said cells are yeast.
20. The method of claim 17, wherein said total cell count is
determined by a method selected from the group consisting of native
UV absorption, turbidity testing, hemacytometer measurements,
fluorescence, and dye exclusion.
21. The method of claim 20, wherein said total cell count is
determined by UV absorption.
22. The method of claim 17, wherein the enzymatic activity is
esterase activity.
23. The method of claim 17, wherein said enzymatically altered dye
or molecule comprises fluorescein diacetate or OREGON
GREEN.TM..
24. The method of claim 17, wherein detection is performed by a
flurorometer.
25. A method for quantitating total and live cells in a sample,
comprising measuring total fluorescence of cells in a sample and
comparing to a standard value, thereby quantitating total cells in
said sample; contacting a sample with a fluorescent dye that is
metabolically altered by live cells; said dye having fluorescence
properties that are measurably altered when modified by live cells,
detecting the metabolic alteration of the dye thereby obtaining a
measurement value and comparing said value to a standard value,
thereby quantitating live cells in said sample.
26. A method for measuring the number of total and live yeast,
bacteria or other cells in a sample, comprising measuring the
native fluorescence of cells in suspension, contacting said cells
with a dye that penetrates into the interior of yeast or bacteria
and is metabolically modified to a measurable parameter by live
cells, measuring the total fluorescence and fluorescence properties
provided by the metabolic alteration of said sample and correlating
said fluorescence to the number of total and live cells in said
sample or a fraction of the sample and determining the percent
viability of said sample.
27. A kit for quantifying yeast or bacteria, comprising a cell
suspension solution, a cell penetrating dye, and instructions for
detecting dye that correlates to hemocytometer counts, plate counts
or other methods of counting viable cells.
28. The kit of claim 27, wherein said dye is a dye that is
enzymatically and detectably altered following penetration of
viable cells.
29. A kit for quantifying yeast or bacteria or mammalian cells,
comprising: a first container containing a first solution, a second
solution containing a compound that penetrates cell membranes and
is metabolized to a fluorescent dye or other detectable dye that is
measurable, and instructions for using the same.
30. The kit of claim 29, further comprising a means for mixing said
first solution with a sample containing an unknown number of living
cells and nonliving cells, means for concentrating the cells from
the mixture of said first solution with said sample and removing
solids from the remainder of said mixture, and measuring native
fluorescence of cells in said solution.
31. The kit of claim 29, further comprising a means for mixing said
second solution with said cells to form a second mixture, and means
for illuminating the mixture of said second solution with said
cells with excitation light and measuring fluorescence emitted by
said mixture, and thereby determining the amount of metabolically
modified dye present in the cells that is proportional to the
number of viable cells in said second solution.
32. The kit of claim 29, further comprising a third solution
containing a compound or compounds that increase the rate of uptake
of dye into cells or speeds up the rate of conversion the
detectable fluorescent form of the dye inside said cells in second
solution.
33. A device that comprises solid fluorescent material consisting
of an adaptor and a compound that can be used to calibrate the
instrumentation used for detecting fluorescence in the cells.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority to U.S. Provisional
Application No. 60/220,298, filed Jul. 24, 2000.
TECHNICAL FIELD
[0002] The present invention relates to methods for the rapid
quantitation of both viable and nonviable cells. More specifically,
the invention involves incubating cells with a metabolically
activated visible fluorescent dye and measuring the fluorescence
generated by viable cells. Total cell populations
(viable+nonviable) are separately determined by measuring the
native UV fluorescence of the cells. The two fluorescence readings
are directly related to the number of viable and nonviable cells.
This permits the user to determine the percent viability of a mixed
population of live and dead cells.
BACKGROUND OF THE INVENTION
[0003] The ability to quantify living cells is vitally important to
the food, beverage, pharmaceutical, environmental, manufacturing
and clinical industries. Several methods are currently employed by
these industries to quantify prokaryotic and eukaryotic cells.
These methods include, but are not limited to, the standard plate
count, dye reduction and exclusion methods, electrometric
techniques, microscopy, flow cytometry, bioluminescence and
turbidity.
[0004] The standard plate count permits the quantitation of living
cells (or clumps of cells) also known as colony forming units (cfu)
when the cells are grown on the appropriate medium under optimal
growth conditions (Microbial Ecology, Atlas, R. M. and Bartha, R.,
Addison Wesley, Longman, N.Y., 1998). Current standards of viable
organism counts are often based on the standard plate count,
particularly in the food industry. However, colony counts are
difficult to interpret since bacteria often clump or form chains
that can give rise to significantly inaccurate estimations of the
total number of viable organisms in a sample. Also, bacteria, for
example, can be in a "metabolically damaged" state and not form
countable colonies on a given medium. This problem is more severe
when selective media are used. Thus, the standard plate count does
not provide a definitive count of viable cells in a sample, which
may be very important for certain purposes. Given these factors,
such testing also requires skilled technicians who can distinguish
individual colony forming units and who can aid in selecting
appropriate growth medium. Moreover, the technique is not useful
when rapid determination of cell counts is required since it often
requires over 24 hours to obtain results.
[0005] Other tests, such as, dye reduction tests rely on the
ability of cells to oxidize or reduce a particular dye (Harrington,
1998). Such methods are used to measure the activity of
metabolically active organisms rather than provide a measure of the
total number of viable cells in a sample. Dyes, such as methylene
blue, coupled with microscopic counting, are routinely employed to
determine the relative number of microorganisms. The technique is
widely employed but nevertheless suffers from factors that must be
held constant during the assay, e.g., medium used, chemical
conditions, temperature and the types of cells being examined.
Also, dye reduction tests that incorporate microscopic counting
techniques require trained technical personnel and often depend on
subjective interpretations.
[0006] Dye exclusion methods of cell quantitation depend on the
living cells having the ability to pump the dye out of the cell and
into the surrounding fluid medium. While the dye may enter the
interior of both living and dead cells, dead cells are not capable
of actively pumping the dye out under the conditions normally used.
Dye exclusion is commonly employed to enumerate animal, fungal and
yeast cells. It is a method requiring skill, correct timing and
proper choice of dye. It is not applicable to certain microbes and
it yields incorrect viable counts with stressed cells.
[0007] An accurate estimation of the number of viable yeast cells
in a sample can be obtained by the slide viability technique
(Gilliland, 1959). The yeast cells are suspended in a growth medium
containing 6% gelatin and the suspension is placed in a
hemocytometer slide. The cell suspension is incubated for
approximately 20 hours and the numbers of micro colonies are
counted. Cells that form micro colonies are viable and dead cells
remain as single cells. This technique is considered by the brewing
industry to be the most definitive test for counting the number of
viable yeast cells. Unfortunately, the long incubation time makes
it unacceptable as a routine method.
[0008] Microscopic techniques typically involve counting a dilution
of cells on a calibrated microscopic grid, such as a hemocytometer.
A recent improvement in this technique is the direct epifluorescent
filter technique (DEFT) (Pettipher et al, 1989). In this technique,
samples are filtered through a membrane filter that traps the cells
to be counted. A fluorescent dye is attached to the cells, which
are illuminated with ultraviolet light and counted. Unfortunately,
the technique requires the use of an expensive microscope and a
trained individual or an expensive automated system (Pettipher et
al., 1989).
[0009] Yet other methods of quantitation use flow cytometry
involves the differential fluorescent staining of cells suspended
in a relatively clear fluid stream of low viscosity. The cell
suspension is mixed with the fluorescent dye and illuminated in a
flow cell by a laser or other light source. The labeled cells are
automatically detected with the use of a fluorescence detector
focused on the cells (Brailsford and Gatley, 1993 and Pinder et al,
1993). The technique requires, and is limited by, expensive
equipment. Some flow cytometric devices have been used by the food
and dairy industry, but their application has been limited by the
high cost of instrumentation.
[0010] Bioluminescence has been routinely employed in the food
sanitation industry to detect and quantify viable organisms and
cells. The method involves the use of luciferin-luciferase to
detect the presence of ATP (Harrington, 1998 and Griffith et al,
1994). When used to quantify cells, the technique depends on the
assumption that there is a constant amount of ATP in a living cell.
ATP levels vary in a single cell over more than two orders of
magnitude, making this method a relatively inaccurate technique for
the enumeration of viable organisms in a sample.
[0011] Turbidity of a liquid sample can also be measured as an
indication of the concentration of cells due to the light
scattering and absorbing qualities of suspended cells (Harrington,
1998). The method is old but it is still employed to estimate the
bacterial concentration in a sample. The method is rapid and simple
but is highly inaccurate since all cells, particles and substances,
including non-living particulate matter, interfere with the
interpretation of the results.
[0012] The present invention for the quantitation of both viable
and nonviable cells is designed to overcome at least five problems
that have been identified within the field. First, the new
technology circumvents the need for training personnel in how to
plate, grow and count viable cells from colonies on agar plates. It
also eliminates nearly all training and maintenance costs
associated with most of the other methods. Second, the invention
substantially decreases the time needed to determine concentrations
of cells such as yeast and bacteria. Under current methodologies,
quantification requires from 24-72 hours (plate count and
enrichment cultures), while the present invention permits accurate
quantitation in less than 15 minutes. The methylene blue test is
rapid; however, the accuracy is unacceptable for cultures that are
less than 90% viable. The slide viability test is accurate for
large viability ranges but the time required for results is not
suitable for routine use. Third, the new test is accurate over wide
ranges of viability and has precision similar to the slide
viability test. Fourth, the instant invention offers substantial
cost savings over existing methods of cell quantitation. Fifth, the
invention permits the simultaneous determination of both viable and
total cells in a sample. This allows the user to accurately
establish the percent viability of a cell sample (the number of
viable cells to total cells). Percent viability is a crucial
measurement in many industries such as, the dairy and beer brewing
industries and is currently carried out by the methylene blue
test.
SUMMARY OF THE INVENTION
[0013] The present invention generally provides methods, kits, and
devices for detecting and quantitating the number and/or percentage
of viable cells in a sample. In one aspect the invention provides a
method for determining the percent viability of cells in a sample,
comprising providing a sample containing said cells, detecting the
total cell count, contacting said cells with molecule or dye that
is detectably altered by enzymatic activity of a viable cell,
detecting enzymatically altered dye or molecule, thereby detecting
the number of viable cells and comparing the number of total cells
with the number of viable cells thereby determining the percent
viability.
[0014] In another aspect, a method for detecting viable cells is
provided that comprises providing a sample containing cells,
contacting said sample with a dye that diffuses or is transported
into said cells and wherein said dye is detectably altered by
enzymatic activity of a viable cell, thereby detecting viable cells
in a sample.
[0015] Yet additional aspects of the present invention include
methods for quantitating viable cells in a sample, comprising
providing a sample containing said cells, contacting said cells
with molecule or dye that is detectably altered by enzymatic
activity of a viable cell, detecting ezymatically altered dye or
molecule, thereby detecting the number of viable cells in said
sample and obtaining a value therefrom and correlating the detected
viable cell value with a standard value, thereby quantitating the
viable cells in said sample.
[0016] Further aspects include methods for quantitating total and
live cells in a sample, comprising measuring total fluorescence of
cells in a sample and comparing to a standard value, thereby
quantitating total cells in said sample; contacting a sample with a
fluorescent dye that is metabolically altered by live cells; said
dye having fluorescence properties that are measurably altered when
modified by live cells, detecting the metabolic alteration of the
dye thereby obtaining a measurement value and comparing said value
to a standard value, thereby quantitating live cells in said
sample.
[0017] Still other aspects of the present invention include methods
for measuring the number of total and live yeast, bacteria or other
cells in a sample, comprising measuring the native fluorescence of
cells in suspension, contacting said cells with a dye that
penetrates into the interior of yeast or bacteria and is
metabolically modified to a measurable parameter by live cells,
measuring the total fluorescence and fluorescence properties
provided by the metabolic alteration of said sample and correlating
said fluorescence to the number of total and live cells in said
sample or a fraction of the sample and determining the percent
viability of said sample.
[0018] In certain embodiments the cells may be of any origin such
as bacteria, yeast, or mammalian. In related embodiment the total
cell count is determined by a method selected from the group
consisting of native UV absorption, turbidity testing,
hemacytometer measurements, fluorescence, and dye exclusion.
[0019] In yet other embodiments, the enzymatic activity that alters
the dye or molecule is esterase activity. In further embodiments
the enzymatically altered dye or molecule is fluorescein diacetate
or OREGON GREEN.TM..
[0020] Other embodiments include measurement by a device such as,
by a flurorometer.
[0021] The invention also provides kits for quantifying yeast or
bacteria, comprising a cell suspension solution, a cell penetrating
dye, and instructions for detecting dye that correlates to
hemocytometer counts, plate counts or other methods of counting
viable cells.
[0022] In certain embodiments the kit includes a dye that is
enzymatically and detectably altered following penetration of
viable cells.
[0023] In certain aspects a kit for quantifying yeast or bacteria
or mammalian cells is provided, comprising: a first container
containing a first solution, a second solution containing a
compound that penetrates cell membranes and is metabolized to a
fluorescent dye or other detectable dye that is measurable, and
instructions for using the same.
[0024] In other embodiments kits of the invention further comprise
a means for mixing said first solution with a sample containing an
unknown number of living cells and nonliving cells, means for
concentrating the cells from the mixture of said first solution
with said sample and removing solids from the remainder of said
mixture, and measuring native fluorescence of cells in said
solution.
[0025] In still yet other embodiments the kits may further comprise
a means for mixing said second solution with said cells to form a
second mixture, and means for illuminating the mixture of said
second solution with said cells with excitation light and measuring
fluorescence emitted by said mixture, and thereby determining the
amount of metabolically modified dye present in the cells that is
proportional to the number of viable cells in said second
solution.
[0026] In other embodiments the kits may further comprise a third
solution containing a compound or compounds that increase the rate
of uptake of dye into cells or speeds up the rate of conversion the
detectable fluorescent form of the dye inside said cells in second
solution.
[0027] A device that comprises solid fluorescent material
consisting of an adaptor and a compound that can be used to
calibrate the instrumentation used for detecting fluorescence in
the cells.
[0028] These and other aspects of the present invention will become
evident upon reference to the following detailed description and
attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is an example of solid calibration standards for an
ultraviolet and visible wavelength fluorometer.
[0030] FIG. 2 is a correlation chart of comparable Easy Count
readings of total cell counts to total cell counts as determined by
methlylene blue.
[0031] FIG. 3 is a correlation chart of comparable Easy Count
readings of viable cell counts to total cell counts as determined
by methlylene blue.
[0032] FIG. 4 is a plot of regression analysis demonstrating the
relationship between the inventive method and those determined by
methylene blue for total cell count.
[0033] FIG. 5 is a plot of regression analysis demonstrating the
relationship between the inventive method and those determined by
methylene blue for viable cell counts.
[0034] FIG. 6 is a linear correlation plot of hemacytometer counts
vs. Easy Count Readings. Data points are the mean of three samples.
The linear relationship is significant P<0.0001.
[0035] FIG. 7 is a linear correlation plot of hemacytometer counts
that have been corrected for viability using methylene blue stain
vs. Easy Count Readings. Data points are the mean of three samples.
The linear relationship is significant P<0.0001.
[0036] FIG. 8 is a linear correlation between percent viability as
measured by slide culture, and Easy Count values. Data points are
the mean of three samples. The linear relationship is significant
P<0.0001.
[0037] FIG. 9 is a plot representing fermentation tracking.
Fermentation tracking in a laboratory fermentation using both the
Easy Count and hemacytometer methods. Time 0 is the time that the
cells were pitched into fresh wort. The Y-axes represent cell
counts using a hemacytometer (squares) and active cells using the
Easy Count (diamonds). Data points are the mean of three
samples.
[0038] FIG. 10 is a pot representing fermentation tracking during
brewery scale fermentation. The Y-axes represent cell counts using
a hemacytometer (squares) and the Easy Count (diamonds). Data
points are the mean of three samples.
[0039] FIG. 11 is a plot depicting Percent error between operators
for the three methods is shown. Methylene Blue dead (stained) cells
reported differences between operators of 28.3%, while Methylene
Blue live (non-stained cells) was 21.0%. The error between
operators for the Easy Count was significantly lower, at only
2.6%.
DETAILED DESCRIPTION
[0040] Briefly, the current invention describes novel methods that
can be used to quantify live cells and total cells (total includes
all cells in the sample, both viable and nonviable) such as yeast
and bacteria. This allows the user to determine percent viability
of the sample of cells. In one aspect, the instant invention
comprises three steps: 1) Determination of total cells, 2)
Determination of viable cells and 3) Calculation of percent
viability. In certain embodiments the total cells are determined by
washing and incubating the cells in a solution and then measuring
the native UV fluorescence of the cells in a fluorometer permit
determination of total cell populations. Subsequently the cells are
incubated with a compound that can be metabolically converted to a
visible fluorescent dye such as fluorescein diacetate, coupled with
an inducer of esterase activity such as dequalinium acetate, and
then measuring the fluorescence thus permitting enumeration of
viable cell populations. The fluorescent readings are correlated to
standard counts such as hemocytometer counts or to the slide
viability counts. The two fluorescence readings are directly
related to the number of total and viable cells respectively. This
permits the user to calculate the percent viability of a mixed
population of live and dead cells.
[0041] As those of ordinary skill in the art can readily appreciate
the present invention may be modified in certain ways to achieve
the same result. In brief, the present invention utilizes one or
more dyes or molecules that allow for the detection of all cells or
total cells (e.g., yeast, bacteria, mammalian, etc.) in a sample
and the same or different one or more dyes that is
metabolized/derivatized by the viable cells in the sample to allow
detection of the viable cells. Accordingly, the percent viability
can then be readily determined. As can be appreciated adding
substances such as detergent-like compounds, surfactants, solvents,
or other compounds that affect membrane polarity, membrane
fluidity, permeability, potential gradient etc., to the sample to
increase the rate at which the molecule or dye enters the cells in
order to speed the process.
[0042] Other variations that are within the scope of the present
invention include adding compounds that affect membrane polarity to
decrease the rate of "leakage" of the converted dye from the cells.
Further, esterase enzyme inducing chemicals may be added to
increase esterase activity in living cells such as naphthalene or
dequalinium acetate or by environmental factors such as heat. In
addition, compounds other than fluorescein diacetate, such as
Calcein AM, may also be used to detect metabolically active live
cells.
[0043] The stability and shelf life of the fluorescein diacetate
and other chemicals may be increased by the addition of
antioxidants or similar preservatives or by dissolving the FDA into
other solvents besides acetone or by other stabilizing methods such
as lyophilization. The fluorescence detection apparatus used may be
designed for microscopic, surface, internal, solution and
non-suspension sample formats.
[0044] Also included within the context of the present invention is
software that permits the user to interface the fluorescence
instrumentation to a computer for direct calculation of percent
viability and cell concentration or other data processing or
recording formats.
[0045] Addition of compounds to reduce background in the sample,
such as hemoglobin may be utilized. Rinsing the sample in a buffer
solution and centrifuging or filtering or otherwise retaining the
cells as they are washed to remove any exogenous background
fluorescence.
[0046] The differences between prokaryotes and eukaryotes may also
utilized to assist detection. For example, such easily detectable
differences include cell membrane receptors, lack of organelles in
prokaryotes, or metabolic differences. These differences can be
utilized to distinguish between prokaryotes and eukaryotes by using
dyes that penetrate only mitochondria or nuclei for example, or to
take advantage of membrane and metabolic differences in these two
cell types. This will allow the user to count a specific prokaryote
or a eukaryote in a mixture of cells that contains both types of
cells. For example, one may determine if bacteria contaminate a
yeast cell or blood cell population.
[0047] Other variations to the present invention include altering
the pH of the reaction solutions to increase the sensitivity of the
reaction. Changing concentrations of the solutes to increase or
decrease the sensitivity of the reaction. Alterations to the solid
standards may be utilized to increase the sensitivity and dynamic
range of the assay. Use of the viability assay to measure overall
health or metabolic or growth status of the cells including ability
to withstand stress. Use of the various steps of the tests
independently, e.g., to measure only total cells or only live
cells.
[0048] Other methods of total cell determination may be made by
using DNA binding dyes, protein stains, cell membrane stains,
antibody coupled stains, lipid dyes or other methods of detecting
total cells in a sample. Viable cells may also be quantified using
other methods that distinguish between live and dead cells such as
surface markers, DNA stains, protein stains, antibody coupled
stains, lipid dyes or other methods of detecting viable cells in a
sample.
[0049] The solid standard can be made out of other materials such
as, but not limited to, plastic, or by embedding chemicals such as
fluorescein in a solid matrix of epoxy, acrylic, polyacrylamide or
agarose or by coating a material like plastic with said chemical.
Other chemicals, which have excitation and emission wavelengths in
the range of the dyes or cells used to carry out the invention,
could be used.
[0050] The instrument can be calibrated with solutions containing
fluorescent chemicals such as fluorescein or OREGON GREEN.TM..
Other configurations of the solid standard can be employed. The
adaptor can be constructed to fit the type and make of instrument
used to carry out the method. Different concentrations of the
reagents may be used to carry out the method. Other methods of
mixing and or concentrating samples may be used. The wash steps may
also be eliminated, thus simplifying the procedure.
[0051] Yet further variations of the present invention include, but
are not limited to, the use of an incubator to control the
temperature of the dye conversion in the cells. Such incubation can
take place in a plate counter or vial heater of some kind. Further,
the samples may be arranged in an array format to allow high
throughput detection.
[0052] The methods and kits of the present invention allow for the
determination of the number of active cells by measuring the rate
of conversion of dye by the cells. The number and activity of said
cells may be determined without reaching the reaction endpoint.
[0053] The methodology has obvious application in determining the
activity of yeast or bacteria in industrial fermentation
applications. Thus, the methods and kits can be used to predict the
number of cells required to carry out fermentation based on viable
cells rather than on total cells.
[0054] As those of ordinary skill in the art can readily
appreciate, the instant invention can be carried out in a single
vessel and solution.
[0055] The instant invention also has applicability in assessing
the activity, vitality, or number of cells under various storage
conditions, comparing the metabolic activity of different cells,
developing pitching rate charts for fermentation applications, and
use of the method as a self-contained laboratory.
[0056] The present invention provides methods, kits and apparatuses
for simple dye associated quantitation that allows one to
inexpensively determine total cell counts and viable cell counts in
a particular sample. An individual of ordinary skill in the art
will readily appreciate that alternatives to the steps herein
described for quantitating cells may be used and are encompassed
herein. Accordingly, all alternatives will use a kit or method
wherein a dye is utilized to stain cells and a method is used to
detect or quantify the dye. One key aspect of this invention is its
ability to simultaneously determine total cells and live cells in a
sample in short times compared to standard methods. In preferred
embodiments, detection is completed in less than 4 hours, in others
in less then about 3 hours, and yet further, in less than about 2
hours, while in specific embodiments, detection is completed in
less than about 1 hour, less then about 45 minutes, less than about
30 minutes, less than about 15 minutes, and less than about 10
minutes at low cost.
[0057] All patents, patent applications and references cited herein
are incorporated in their entirety. Accordingly, incorporated
herein by reference are U.S. Pat. Nos. 5,437,980; 5,563,070;
5,582,984; 5,658,751; 5,436,134; 5,939,282; 4,783,401;
3,586,859
EXAMPLES
Example I
Materials and Calibration
[0058] The following shows examples of solutions, volumes and
concentrations that can be used to carry out the invention. Other
concentrations and volumes and different buffers with different pH
values may be used. The samples and reaction solutions may be
provided in any volume necessary for detection, however, in the
present embodiment, small volumes (less than 1 ml) are utilized
such that reagents and sample amounts are kept to a minimum. The
volumes and concentrations to be utilized are any that are
convenient to the practitioner of the methodology. In certain
embodiments, the sample and reagent amounts range from 1 to 10,000
micro liters.
[0059] The reader used in the present embodiment is a "picofluor"
hand-held fluorometer from Turner Designs, Sunnyvale, Calif. 94086.
Any fluorometer that can measure fluorescence at specific
wavelengths for detection of the dyes or cells can be employed in
the invention. Ideally, the fluorometer can switch back and forth
from visible (486 nm excitation with a 10 nm bandwidth and 550
emission with a 10 nm bandwidth) and UV (300-400 nm excitation and
410-700 nm emission) modes without changing filters or making other
adjustments; however, this is not necessary to carry out the
methodology. Other wavelengths may be used in combination with
different dye types or cell types. The wavelength chosen will be
dependent on the dye or cell type chosen for staining.
[0060] The instrument needs to be calibrated in a range that
permits quantitation of cells. Calibration can be carried out with
solutions such as fluorescein or Oregon green or with the use of
solid standards as described below.
[0061] Materials
[0062] Solid Calibration Standards:
[0063] Materials
[0064] Colored glass rods: Mint green for the visible mode
calibration, and translucent blue for the ultraviolet (UV) mode
calibration.
[0065] Solid calibration adapter: Black diacetyl plastic machined
to fit the instrument.
[0066] Glass rods are glued into the solid calibration adapter and
sealed with a plastic cap, (See FIG. 1).
[0067] Solutions A (Cell Preparation): 1.times. PBS
[0068] Ingredients (for 10.times. stock solution)
[0069] 80 grams NaCl
[0070] 2.0 grams KCl
[0071] 14.4 grams Na.sub.2HPO.sub.4
[0072] 2.4 grams KH.sub.2PO.sub.4
[0073] NaOH (enough to reach a PH of 7.4)
[0074] This recipe makes a 10.times. stock solution. It must be
diluted 1:10 into distilled water to make a 1.times. working
solution before being used.
[0075] Solution B (Live Cell Suspension):
[0076] Ingredients: 0.0275 grams dequalinium acetate in 30 mL
10.times. Sodium acetate buffer: (13.6 grams Sodium acetate in 100
mL ddH.sub.2o)
[0077] Stock Solution C (Live Cell Reaction Stock):
[0078] Ingredients:
[0079] Fluorescein diacetate (FDA), 30 mg/10 mL in Acetone
[0080] Protocol
[0081] I. Calibration Using Solid Standards
[0082] To calibrate the instrument in "A" mode (UV): Standard
Value=500
[0083] 1) Remove the mini cell receptacle from the instrument.
[0084] 2) Be sure that the instrument is in "A" mode; the letters
UV should appear in the lower left corner of the screen.
[0085] 3) If the instrument is not in "A" mode, press the A/B key
on the instrument keypad.
[0086] 4) Press the CAL key on the keypad; when prompted, press
ENTER to continue.
[0087] 5) When asked to insert the blank, insert the solid standard
labeled "A" into the instrument with the letter "A" facing down and
to the right.
[0088] 6) When asked to insert the "cal", insert the solid standard
labeled "A" into the instrument so that the letter A is facing
towards you, and the white cap is on top.
[0089] To calibrate the instrument in "B" mode (Visible): Standard
Value=500
[0090] 1) Follow all the instructions for calibration in "A" mode,
making sure that that the instrument is now in "B" mode, and that
the solid standard labeled "B" is now being used.
EXAMPLE II
Total Cell Counts
[0091] Total cell counts can be determined by a variety of
methodologies, including using the fluorometer noted above. UV
operation mode is selected. A fixed volume (200 microliters) of
Cell preparation solution is added to the glass sample vial. 5
microliters of sample (yeast cells) is then added to the Cell
preparation solution in the vial and centrifuged for about 30
seconds to sediment the a cell pellet. The cell pellet is
resuspended in about 100 microliters of Cell preparation solution
to the sample vial. The sample vial is then read in fluorometer.
See FIG. 2.
EXAMPLE III
Viable Cell Counts
[0092] Live cells are quantitated utilizing a dye that is
detectably altered by an intracellular enzyme. For example, the
fluorometer noted above is set in visible mode and a fixed volume
(200 microliters) of Cell preparation solution is added to the
sample vial. 5 microliters of sample is added to the solution A in
the sample vial and centrifuged for 30 seconds. 100 microliters of
Suspension solution is added to the sample vial and 5 microliters
of Reaction solution is added to the sample vial. The sample is
mixed and placed in the reader and fluorescence determined at time
zero and again at 15 minutes. This is the value that will be
compared to the Easy Count correlation chart for conversion to
cells/ml. See FIG. 3.
EXAMPLE IV
Yeast Quantitation
[0093] Yeast performance is critical to the development of quality
beer. For this reason, methods of yeast analysis are an important
element of the brewing process. Traditional methods including
hemacytometer counting and methylene blue staining are rapid, but
inaccurate and unreliable. Slide culture is an accurate measure of
yeast viability, but requires a lengthy incubation period of 18 to
24 hours. As an alternative, the fluorometric assay, described
above is based on the metabolic activity of the yeast culture to
provide brewers with a rapid and accurate estimation of active cell
number. This method was compared to the hemacytometer counting
technique as an estimation of cell number, and to both methylene
blue staining and slide culture as measures of vitality and
prediction of fermentation performance. The inventive method
correlated to the hemacytometer, methylene blue, and slide culture
with R.sup.2 values of 0.985, 0.987, and 0.962 respectively,
P<0.0001. An error analysis was carried out by the inventive
methods, hemacytometer and methylene blue staining techniques for
multiple operators performing the tests. Thus, the present
invention could be used to determine correct pitching rates,
monitor fermentation and propagation, and for other applications
involving cell quantitation.
[0094] Yeast
[0095] All yeast cultures were obtained from Wyeast Laboratories,
Mt. Hood, Oreg. Yeast samples for the experiments comparing the
hemacytometer, methylene blue staining, and slide culture to the
inventive methods were a 1084 strain of Saccharomyces cerevisiae.
Yeast cultures tested during laboratory scale fermentations were
strain 1968. Brewery scale fermentations were performed using yeast
strain 1056.
[0096] Hemacytometer Counts
[0097] Hemacytometer counts were performed according to the ASBC
method (6, 8). Samples were removed from a slurry with an initial
concentration of 198 million cells per ml, as determined by
hemacytometer count, and diluted in spent wort to maintain cell
integrity. Each dilution was counted in the hemacytometer as well
as measured using the present method. Experiments were carried out
in triplicate.
[0098] Methylene Blue Staining
[0099] Methylene blue staining was performed according to the ASBC
method (6, 8). Samples were removed from a slurry with an initial
concentration of 198 million cells per ml, as determined by
hemacytometer count, and diluted in spent wort to maintain cell
integrity. Each dilution was stained and counted in a
hemacytometer, as well as measured using the present method.
Hemacytometer counts were corrected for viability according to the
staining results. Experiments were carried out in triplicate.
[0100] Slide Culture
[0101] Slide culture was performed according to a modified version
of the protocol for preparation of slide cultures for the
examination of yeast and mold (5). Ten ml of yeast strain 1028 at a
concentration of 433 million cells per milliliter, as determined by
a hemacytometer count, were placed into a 43 degree Celsius water
bath. Aliquots were removed at time intervals 0, 2, 4, 6, 8, 10,
15, 20, 30, and 40 minutes. Each was tested using the inventive
method. Measurements were taken in triplicate and averaged. Slide
culture samples were diluted 1:100 into wort containing 6% gelatin.
10 .mu.l of the sample were then placed on a micro slide, covered
and sealed with petroleum jelly. Each slide was incubated for 20
hours at 18 degrees Celsius before microscopic examination
(Microscope model, Leica DMLB). Viability was determined with the
assumption that living cells had formed micro colonies, while
nonviable cells remained single.
[0102] Determination of Active Cell Number Using the Instant
Invention
[0103] The inventive method for determining total active cell
number is based on the metabolic activity of the yeast culture. The
technology involves exposing cells to proprietary chemicals that
enter cells through diffusion. These molecules are converted to a
fluorescent form by metabolically active cells. This fluorescent
signal is quantified in a handheld battery operated fluorometer
model GP320 GenPrime Inc, Spokane, Wash. The protocol is as
follows; 50 .mu.l of yeast sample was added to 500 .mu.l of cell
prep solution in a 1 ml glass test cuvette. 50 .mu.l of dye
solution was added; the cuvette was capped, and incubated for 5
minutes. After incubation, the cuvette was shaken, and the
fluorescent signal quantitated in the GP320. These values were
compared to the hemacytometer and methylene blue staining methods
by performing tests with the inventive method on the diluted
samples from these experiments. Readings were taken in triplicate
and averaged. These relationships were analyzed by linear
regression using Statview, SAS institute, Cary N.C.
[0104] Fermentation Tracking
[0105] Laboratory Scale:
[0106] Laboratory scale fermentation tracking was carried out in a
300 ml flask by inoculating 150 ml wort with 5 ml yeast strain
1968, with an initial concentration of 420 million cells per ml,
and monitoring growth using a hemacytometer and the inventive
methods. Cells were grown at room temperature (21.degree. C.).
Samples were taken every 45 minutes for 5.25 hours and then
periodically over the next 48 hours.
[0107] Brewery Scale:
[0108] Brewery Scale fermentation tracking was carried out during a
typical fermentation cycle, at the Steam Plant Grill, Spokane,
Wash. 99201. Hemacytometer counts and corresponding readings using
the instant invention were made daily for 13 days beginning
immediately following pitching.
[0109] Error
[0110] Percent error between operators was determined for the
inventive method "Easy Count" method, hemacytometer counts, and the
methylene blue staining method. Error analysis was performed using
Microsoft Excel.
[0111] Hemacytometer:
[0112] Three operators performed hemacytometer analysis of a yeast
strain 1028 slurry according to the ASBC method. Each operator
prepared and measured 15 samples. Results were averaged for each
operator, and error between operators was calculated.
[0113] Methylene Blue:
[0114] The 15 hemacytometer samples from above were stained with
methylene blue according to the ASBC method. Each of the three
operators counted stained cells for each sample. Results were
averaged for each operator, and error between operators was
calculated.
[0115] Easy Count:
[0116] Easy Count tests were performed on 15 replicate samples by
each of the three operators. Results were averaged for each
operator, and error between operators was calculated.
[0117] Hemacytometer Counts
[0118] FIG. 6 shows the correlation between the Easy Count values
and the cells/ml results of the hemacytometer. A statistically
linear relationship was found between cell counts obtained by the
ASBC standard method of microscopic examination using a
hemacytometer and values obtained using the Easy Count,
R.sup.2=0.985.
[0119] 6
[0120] Methylene Blue Staining
[0121] FIG. 7 illustrates the linear correlation found between the
Easy Count method and the ASBC method for methylene blue staining.
A statistically linear relationship was found between the Easy
Count, and hemacytometer counts corrected for viability,
R.sup.2=0.987
[0122] 7
[0123] These results suggest that the Easy Count can be used to
accurately predict active cell number. Using the results of the
correlation, it is possible for the brewer to accurately determine
the correct pitching rate using the Easy Count method based on 1
million active cells per ml per degree plato of wort. Additionally,
the method can be used to monitor fermentation, propagation, and
for other applications involving the quantitation of cells.
[0124] Slide Culture
[0125] A linear relationship was found between the Easy Count and
slide culture for yeast viability, as shown in FIG. 8.
[0126] 8
[0127] The correlation to slide culture confirms that the Easy
Count only measures active cells, since the total number of cells
in this experiment remains constant.
[0128] Fermentation Tracking
[0129] Cell growth was measured during laboratory and brewery scale
fermentations using both the ASBC method for hemacytometer counts,
and the Easy Count method. FIG. 9 shows cell growth tracked by both
methods during laboratory scale fermentation. FIG. 10 is an example
of a brewery scale fermentation tracked by both methods.
[0130] Error
[0131] Results from the experiments were averaged for each operator
as shown in Table 1. Percent error between operators was calculated
by dividing the standard deviation of the mean by the mean, and
multiplying the result by 100. Easy Count reported significantly
lower error between operators than the other methods. These results
are graphed in FIG. 11.
1 Data in Easy Methylene Methylene Millions Count Blue live Blue
dead of cells/ml mean mean mean Operator 195.9 158.6 27.9 1
Operator 197 122.3 23.6 2 Operator 187.7 187.7 40.3 3 Mean 193.5
156.2 30.6 Std. Dev. 5.1 32.8 8.7 % Error 2.6 21.0 28.3
[0132] Results of the error experiments confirm previous research
reporting the inaccuracies of hemacytometer counts and methylene
blue staining (1, 2, 3, 4, 7). The low error associated with the
Easy Count method is an improvement on these traditional
techniques.
[0133] Percent error is of particular importance to the brewer due
to the exacerbation of inaccuracies in the calculation of cells/ml.
For example, when calculating cells/ml from a hemacytometer count
of 180 live cells, and 15 dead cells, (counting all 25 fields and
using a 1:100 dilution) the result would be 180 million live
cells/ml (180*100*10000) and 15 million dead cells/ml
(15*100*10000). If the error between operators when performing the
live cell test is 21%, then the live cell result could be between
142-218 million cells/ml, a difference of 76 million cells/ml. With
a percent error of 28% between operators, the dead cell result
could be between 11-19 million cells/ml. This could result in
reported viabilities between 87% and 96% for the same sample. The
Easy Count has much less error associated with its performance. A
reading of 6000 in the Easy Count would be 197 million active
cells/ml (see equation generated in FIG. 7.). A percent error of 3%
between operators gives a range between 191-203 million cells/ml, a
difference of only 12 million cells/ml. The very low error
associated with the performance of the Easy Count provides much
more reliable information to the brewer.
[0134] 1. Mochaba, F. et al, Practical Procedures to Measure Yeast
Viability and Vitality Prior to Pitching. J. Am. Soc. Brew. Chem.
56(1): 1-6, 1998.
[0135] 2. O'Connor-Cox, E. et al, Methylene Blue Staining: use at
your own risk. Tech. Q. Master. Brew. Assoc. 34:306-312, 1997
[0136] 3. Carvell J. P. et al Developments in Using Off-Line Radio
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2000
[0137] 4. Smart, K. A. et al Use of Methylene Violet Staining
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* * * * *