U.S. patent application number 13/840509 was filed with the patent office on 2014-09-18 for sterilization indicator of oxidative sterilants.
This patent application is currently assigned to AMERICAN STERILIZER COMPANY. The applicant listed for this patent is AMERICAN STERILIZER COMPANY. Invention is credited to Tricia A. Cregger, Phillip P. Franciskovich.
Application Number | 20140273073 13/840509 |
Document ID | / |
Family ID | 50272749 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140273073 |
Kind Code |
A1 |
Franciskovich; Phillip P. ;
et al. |
September 18, 2014 |
STERILIZATION INDICATOR OF OXIDATIVE STERILANTS
Abstract
A sterilization indicator for oxidative sterilants, comprising a
first compartment comprising spores of one or more microorganism
species, wherein the spores have been pretreated with and comprises
a compound comprising a transition metal ion that is reactive with
an oxidative sterilant; a second compartment comprising a growth
medium and adapted to combine contents of the first compartment
with contents of the second compartment for incubation after the
sterilization indicator has been exposed to an oxidative sterilant;
and an agent disposed in the growth medium and selected to indicate
viability of the spores after the sterilization indicator has been
exposed to the oxidative sterilant.
Inventors: |
Franciskovich; Phillip P.;
(Concord, OH) ; Cregger; Tricia A.; (Fairlawn,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AMERICAN STERILIZER COMPANY |
Mentor |
OH |
US |
|
|
Assignee: |
AMERICAN STERILIZER COMPANY
Mentor
OH
|
Family ID: |
50272749 |
Appl. No.: |
13/840509 |
Filed: |
March 15, 2013 |
Current U.S.
Class: |
435/31 ;
435/287.4 |
Current CPC
Class: |
C12Q 1/22 20130101; A61L
2/28 20130101 |
Class at
Publication: |
435/31 ;
435/287.4 |
International
Class: |
C12Q 1/22 20060101
C12Q001/22 |
Claims
1. A sterilization indicator for oxidative sterilants, comprising:
a first compartment comprising spores of one or more microorganism
species, wherein the spores have been pretreated with and comprises
a compound comprising a transition metal ion that is reactive with
an oxidative sterilant; a second compartment comprising a growth
medium and adapted to combine contents of the first compartment
with contents of the second compartment for incubation after the
sterilization indicator has been exposed to an oxidative sterilant;
and an agent disposed in the growth medium and selected to indicate
viability of the spores after the sterilization indicator has been
exposed to the oxidative sterilant.
2. The sterilization indicator of claim 1 wherein the one or more
microorganism species comprises one or both of Geobacillus
stearothermophilus and Bacillus atrophaeus.
3. The sterilization indicator of claim 1 wherein the agent
indicates viability of the spores by means of one or more of a
color change, a turbidity change, production of fluorescence or an
electrically detectable reaction.
4. The sterilization indicator of claim 3 wherein the agent is a pH
indicator.
5. The sterilization indicator of claim 4 wherein the pH indicator
comprises Brilliant Green, Bromocresol Green, Bromocresol Purple,
Bromothymol Blue, Cresol Red, Methylene Blue, Neutral Red, Phenol
Red, Resazurin, or Thymol Blue.
6. The sterilization indicator of claim 3 wherein the agent is a
fluorescence indicator.
7. The sterilization indicator of claim 6 wherein the fluorescence
indicator is a color-shifting fluorescent protein.
8. The sterilization indicator of claim 3 wherein the agent
comprises at least two electrodes adapted to provide a detectable
electrical signal.
9. The sterilization indicator of claim 3 wherein the agent
comprises a tetrazolium salt.
10. The sterilization indicator of claim 1 wherein the transition
metal ion comprises one or more of iron, copper, manganese,
titanium, zinc, vanadium, silver, platinum, nickel, molybdenum,
cobalt and chromium.
11. The sterilization indicator of claim 8 wherein the transition
metal ion is iron in K.sub.3[Fe(CN).sub.6] or
Fe.sub.7(CN).sub.18.
12. The sterilization indicator of claim 1 wherein the oxidative
sterilant comprises one or more of hydrogen peroxide, ethylene
oxide and ozone.
13. A process for determining the efficacy of a sterilization
process utilizing oxidative sterilants, comprising: providing a
sterilization indicator according to claim 1; exposing the
sterilization indicator and one or more item to be sterilized to an
oxidative sterilant; and determining by inspection of the incubated
growth medium whether the sterilization was effective.
Description
TECHNICAL FIELD
[0001] The present invention relates to biological indicators for
testing the efficacy of sterilization processes, more specifically,
to an improved indicator for use with oxidative sterilants, which
allows monitoring of the effects of the sterilant on a biological
indicator further into the sterilization cycle than conventional
biological indicators used with oxidative sterilants.
BACKGROUND
[0002] One of the most important classes of indicators are the
biological indicators (BI). Biological indicators provide the
highest degree of assurance that sterilization conditions were met
throughout the processed load. This type of indicator is meant to
represent the worst case for the processing system by providing
within or on the indicator an extremely high number of organisms
highly resistant to that particular process. Usually bacterial
spores are the organism of choice for monitoring sterilization
systems.
[0003] Biological indicators typically consist of microorganisms
inoculated onto a carrier material. The microorganisms are
typically bacterial spores that are known to be very resistant to
the particular sterilization medium in which they are to be used.
The carrier material can range from paper to plastic to stainless
steel and may be in a variety of configurations ranging from flat
surfaces to containers such as vials. Biological indicators that
consist of vials and caps are known as self-contained biological
indicators (SCBIs) because they contain all the elements required
to process, activate and incubate the samples. The carrier is
placed into a sterilization cycle along with the medical device
load. Following completion of the cycle the biological indicator is
incubated and monitored for growth for up to seven days. Growth of
a biological indicator indicates that the sterilization process was
not adequate to attain complete sterilization and that the medical
device load needs to be reprocessed before use. No growth of a
biological indicator confirms that conditions within the sterilizer
were adequate to kill at least the number of bacterial spores
loaded onto the indicator (e.g., 10.sup.6 bacterial spores) and
therefore provides a level of assurance that the medical device
load is sterile.
[0004] The resistance of biological indicators to a particular
sterilization process is determined both by the spore utilized and
by the configuration of the biological indicator (e.g., SCBI or
SCBI in a Process Challenge Device). Therefore, to change the
resistance either the sporulation method needs to be altered or a
new physical configuration of the biological indicator needs to be
developed. Having various sporulation methods for different
biological indicators used in different sterilization processes is
not desirable from a manufacturing perspective. Designing a new
physical configuration for a biological indicator can get costly,
for example, because new molds may be needed. Therefore, it is
desirable to be able to alter the resistance of a pre-existing
biological indicator in a simple manner.
[0005] Vaporous hydrogen peroxide and other oxidative sterilization
processes are very effective at killing even resistant organisms
such as spores. This is beneficial to hospitals, since it allows
many heat sensitive medical devices to be processed through
sterilizers using vaporous hydrogen peroxide (VHF) and other
oxidative sterilants. However, the rapid kill that results from
such oxidative sterilants makes it difficult to develop biological
indicators that effectively monitor very far into the sterilization
cycle. That is, because when conventional biological indicators are
used in oxidative sterilant sterilization processes, the organisms
in the biological indicators are so rapidly killed, it is less
certain that an effective dose of the oxidative sterilant has
reached and been maintained at effective levels to all portions of
the load of medical devices as would be the case if the indicator
were killed more slowly.
[0006] Thus, a need for a solution to the previously un-solved
problem of too-rapid kill of biological indicators by oxidative
sterilants has existed for some time. The present invention is
intended to address this problem.
SUMMARY
[0007] The inventive concept described in this disclosure includes
the use of chemical additives to the biological indicator, in which
the chemical additive slows the kill kinetics of spores when
exposed to oxidative sterilants such as vaporous hydrogen peroxide,
ethylene oxide and ozone. In the present invention, spores are
propagated and harvested as usual but before inoculating the
biological indicator with the spores, the spores are resuspended
(at use concentration) in a chemical solution. The chemical
solution includes at least one chemical, e.g., a transition metal,
that inhibits the action of oxidative sterilants such as hydrogen
peroxide, ethylene oxide and ozone, or breaks down or decomposes
the oxidative sterilant into non-reactive components.
[0008] For purposes of the present invention, actions of the
chemical additives may include one or more of (a) inhibition of the
action of the oxidative sterilant, which may include complex
formation, and (b) the breakdown or decomposition of the oxidative
sterilant, which may include catalytic decomposition and/or
chemical neutralization reactions. These additives are generally
referred to as reacting (and cognate terms such as reaction or
being reactive) with the oxidative sterilant. Thus, the term
"reactive with an oxidative sterilant" is deemed, for purposes of
the present invention, to include any action which slows the kill
kinetics of spores in the biological indicator, specifically
including both inhibition of the action of and decomposition and/or
neutralization of, the oxidative sterilant.
[0009] Thus, in accordance with embodiments of the present
invention, there is provided a sterilization indicator for
oxidative sterilants, comprising: [0010] a first compartment
comprising spores of one or more microorganism species, wherein the
spores have been pretreated with and comprises a compound
comprising a transition metal ion that is reactive with an
oxidative sterilant; [0011] a second compartment comprising a
growth medium and adapted to combine contents of the first
compartment with contents of the second compartment for incubation
after the sterilization indicator has been exposed to an oxidative
sterilant; and [0012] an agent disposed in the growth medium and
selected to indicate viability of the spores after the
sterilization indicator has been exposed to the oxidative
sterilant.
[0013] In one embodiment, the one or more microorganism species
comprises one or both of Geobacillus stearothermophilus and
Bacillus atrophaeus, in the form of spores.
[0014] In one embodiment, the agent indicates viability of the
spores by means of one or more of a color change, a turbidity
change, production of fluorescence or an electrically detectable
reaction.
[0015] In one embodiment, the agent is a pH indicator. In one
embodiment, the pH indicator comprises Brilliant Green, Bromocresol
Green, Bromocresol Purple, Bromothymol Blue, Cresol Red, Methylene
Blue, Neutral Red, Phenol Red, Resazurin, or Thymol Blue.
[0016] In one embodiment, the agent is a fluorescence indicator. In
one embodiment, the fluorescence indicator is a color-shifting
fluorescent protein.
[0017] In one embodiment, the agent comprises at least two
electrodes adapted to provide a detectable electrical signal.
[0018] In one embodiment, the agent comprises a tetrazolium
salt.
[0019] In one embodiment, the transition metal ion comprises one or
more of iron, copper, manganese, titanium, zinc, vanadium, silver,
platinum, nickel, molybdenum, cobalt and chromium.
[0020] In one embodiment, the transition metal ion is iron in
K.sub.3[Fe(CN).sub.6] or Fe.sub.7(CN).sub.18. Potassium
ferrocyanide normally has water of hydration, and may be expressed
as K.sub.4[Fe(CN).sub.6].3H.sub.2O. It is noted that Prussian blue
may also be identified by the formula
[Fe.sub.4[Fe(CN).sub.6].sub.3], which is empirically the same as
Fe.sub.7(CN).sub.18. It is noted that the idealized formula for
Prussian blue is Fe.sub.7(CN).sub.18, but that Prussian blue
normally has water of hydration. In one embodiment, the Prussian
blue has a formula Fe.sub.7(CN).sub.18.xH.sub.2O where x is usually
14-16. Prussian blue is normally employed as a very fine colloidal
dispersion, since it is not soluble in water.
[0021] In one embodiment, the oxidative sterilant comprises one or
more of hydrogen peroxide and ozone.
[0022] In one embodiment, the present invention further provides a
process for determining the efficacy of a sterilization process
utilizing oxidative sterilants, comprising: [0023] providing a
sterilization indicator according to any of the preceding claims
[0024] exposing the sterilization indicator and one or more item to
be sterilized to an oxidative sterilant; and [0025] determining by
inspection of the incubated growth medium whether the sterilization
was effective.
DETAILED DESCRIPTION
[0026] Hydrogen peroxide in the vaporous state is very effective at
killing microorganisms but this killing effectiveness makes it
difficult to design and develop biological indicators in the
traditional way that monitor a significant portion of the cycle. An
effective means of increasing the inherent resistance of a
biological indicator is to add a component that inhibits the action
of the active sterilant or breaks the active sterilant into
non-reactive components.
[0027] The concentration of the additives in solution can be varied
to tune in or adjust the resistance of the biological indicator to
effectively monitor more of the sterilization cycle. Biological
indicators, especially in oxidative chemistries such as vaporous
hydrogen peroxide, are quickly killed and will usually only monitor
the very first minutes (or seconds in some conventional products)
of a sterilization cycle.
[0028] The present invention beneficially provides biological
indicators that monitor more of the cycle than just the first few
minutes or seconds of sterilization.
[0029] Oxidative chemicals can be decomposed into non-reactive
components in the presence of certain reactive chemicals. For
example, it has been found that vaporous hydrogen peroxide
decomposes in the presence of most transition metals such as iron,
copper, nickel and manganese. When materials containing these
metals are processed through a vaporous hydrogen peroxide
sterilizer, it has been found that the concentration of peroxide in
the vicinity of these materials is decreased due to the
decomposition of the hydrogen peroxide to non-reactive components.
The present invention takes advantage of this finding to slow down
the kill kinetics in biological indicators used to monitor
oxidative sterilants, such as vaporous hydrogen peroxide.
[0030] In accordance with the present invention, transition metal
reagents comprising iron, copper, nickel and manganese compounds,
are used to react with oxidative sterilants to inhibit the effect
of the oxidative sterilant on the biological indicator employed in
the sterilization indicator used in oxidative sterilization
processes. Iron compounds have been found to decompose hydrogen
peroxide into non-reactive components. For example, two preferred
iron compounds are potassium ferricyanide and Prussian blue.
Potassium ferricyanide is soluble in water and Prussian blue,
although not soluble in water, forms a fine colloidal dispersion in
water.
[0031] In one embodiment of the present invention, there is
provided a sterilization indicator for oxidative sterilants,
including a first compartment comprising spores of one or more
microorganism species, wherein the spores have been pretreated with
and comprise a compound comprising a transition metal ion that is
reactive with an oxidative sterilant; a second compartment
comprising a growth medium and adapted to combine contents of the
first compartment with contents of the second compartment for
incubation after the sterilization indicator has been exposed to an
oxidative sterilant; and an agent disposed in the growth medium and
selected to indicate viability of the spores after the
sterilization indicator has been exposed to the oxidative
sterilant.
[0032] The first and second compartments may be any suitable,
conventional sterilization indicator device, such as a vial with a
cap adapted to hold the growth medium, and a container into which
the spores can be placed. The spores may be directly placed into
the container, or they may be positioned on a carrier which is then
placed in the carrier. One such suitable vial is disclosed in U.S.
Patent Published Application No. US 2010/0081165, which may be
consulted for additional details. US 2010/0081165 is incorporated
herein by reference for its teachings relating to the configuration
of the vial. Another suitable sterilization indicator includes a
carrier and a support, with a biological indicator supported by the
carrier. One such suitable carrier and support is disclosed in U.S.
Patent Published Application No. 2012/0196355, which may be
consulted for additional details. US 2012/0196355 is incorporated
herein by reference for its teachings relating to the configuration
of the carrier, support and biological indicator. Other suitable
sterilization indicators having two compartments, one containing a
biological indicator and one containing a growth medium, may be
suitably selected for use with the present invention by persons of
skill in the art.
[0033] As noted above, in one embodiment, the one or more
microorganism species comprises one or both of Geobacillus
stearothermophilus and Bacillus atrophaeus, in the form of spores.
These two microorganisms are commonly used in biological
indicators. Geobacillus stearothermophilus is more commonly used
with vaporous hydrogen peroxide, and Bacillus atrophaeus is more
commonly used for ethylene oxide sterilants.
[0034] In one embodiment, the agent indicates viability of the
spores by means of one or more of a color change, a turbidity
change, production of fluorescence or an electrically detectable
reaction. The agent may be suitably selected by the person of skill
in the art. In general, the agent can be any suitable agent. The
important feature of the present invention is the ability to slow
down the killing of the spores, and the indicator is only to
indicate the worst-case scenario when the spores have not all been
killed. The following agents are considered suitable, but
additional agents may be used instead, as will be understood by the
skilled person.
[0035] In one embodiment, the agent is a pH indicator. In one
embodiment, the pH indicator comprises Brilliant Green, Bromocresol
Green, Bromocresol Purple, Bromothymol Blue, Cresol Red, Methylene
Blue, Neutral Red, Phenol Red, Resazurin, or Thymol Blue. In one
embodiment, the pH indicator is Bromocresol Purple, and in another
embodiment, the pH indicator is Phenol Red.
[0036] In one embodiment, the agent is a fluorescence indicator. In
one embodiment, the fluorescence indicator is a color-shifting
fluorescent protein. Such color-shifting fluorescent proteins are
known in the art. See, e.g., Macmillan, "Color-shifting fluorescent
proteins highlight biology," Vanderbilt University Medical Center
Reporter, 2009. See also, e.g., Subach, et al., "Monomeric
fluorescent timers that change color from blue to red report on
cellular trafficking", Nature Chemical Biology 5, 118-126 (2009),
and Terskikh, et al., "`Fluorescent Timer`: Protein That Changes
Color with Time", Science, Vol. 290 no. 5496 pp. 1585-1588 (2000).
Other fluorescent indicators may be suitably selected by the person
of skill in the art.
[0037] In one embodiment, the agent comprises at least two
electrodes adapted to provide a detectable electrical signal. The
detectable electrical signal may be detected by, for example, a
strip having two or more electrodes, such as disclosed in either of
U.S. application Ser. No. 13/832,158, entitled COUPLED ENZYME-BASED
METHOD FOR ELECTRONIC MONITORING OF BIOLOGICAL INDICATOR, filed 15
Mar. 2013, or U.S. application Ser. No. 13/836,787, entitled
NON-ENZYME BASED DETECTION METHOD FOR ELECTRONIC MONITORING OF
BIOLOGICAL INDICATOR, filed 15 Mar. 2013, may be suitably selected
for use in detecting an electrical signal.
[0038] In one embodiment, the agent comprises a tetrazolium salt.
Suitable tetrazolium salts include, for example,
3-(4,5-Dimethyl-2-thiazolyl(-2,5-diphenyl-2H-tetrazolium bromide
(MTT), iodonitrotetrazolium chloride (INT), sodium
3,3,-[(Phenylamino)carbonyl]-3,4-Tetrazolium-Bis(4-methoxy-6-nitro)benzen-
esulfonic acid hydrate (NTT), and
4-[3-(4-Idophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene
disulfonate (WST-1). As is known in the art, cleavage of
tetrazolium salts by enzymes of cells which are metabolically
active lead to the formation of detectable products, such as
formazan crystals. If these formazan salts are water soluble
colorimetric measurements can be made directly at the end of the
assay using the supernatant. If the formazan salt is not soluble in
water, solubilization of the crystals must be performed before
light absorbance measurements can be made. For the present
invention, the water soluble formazan salts are preferred.
[0039] In one embodiment, the transition metal ion comprises one or
more of iron, copper, manganese, titanium, zinc, vanadium, silver,
platinum, nickel, molybdenum, cobalt and chromium. Any suitable
transition metal reagent may be used. In one embodiment, the
transition metal reagent is one or a combination of iron, copper,
nickel or manganese compounds. Iron compounds are particularly
effective for use in deactivating hydrogen peroxide. Copper
compounds are effective for use in deactivating ethylene oxide.
Iron and manganese compounds are effective for use in deactivating
ozone. Other transition metal compounds known to react with
oxidizing sterilants such as those used in the present invention
may be suitably selected for use with the present invention by
persons of skill in the art.
[0040] In one embodiment, the transition metal ion is iron in the
form of potassium ferrocyanide, K.sub.3[Fe(CN).sub.6] or iron in
the form of Prussian blue, Fe.sub.7(CN).sub.18. Potassium
ferrocyanide normally has water of hydration, and may be expressed
as K.sub.4[Fe(CN).sub.6].3H.sub.2O. It is noted that Prussian blue
may also be identified by the formula
[Fe.sub.4[Fe(CN).sub.6].sub.3], which is empirically the same as
Fe.sub.7(CN).sub.18. It is noted that the idealized formula for
Prussian blue is Fe.sub.7(CN).sub.18, but that Prussian blue
normally has water of hydration. In one embodiment, the Prussian
blue has a formula Fe.sub.7(CN).sub.18.xH.sub.2O where x is usually
14-16. Prussian blue is normally employed as a very fine colloidal
dispersion, since it is not soluble in water.
[0041] In one embodiment, the oxidative sterilant comprises one or
more of hydrogen peroxide and ozone.
[0042] In one embodiment, the present invention further provides a
process for determining the efficacy of a sterilization process
utilizing oxidative sterilants, comprising: [0043] providing a
sterilization indicator according to any of the preceding [0044]
exposing the sterilization indicator and one or more item to be
sterilized to an oxidative sterilant; and [0045] determining
effectiveness by subsequent growth and color change of the pH
indicator.
[0046] As will be understood by the person of skill in the art, the
basics of the sterilization process described herein are
substantially similar to those known in the art, except for the
provision of the spores of one or more microorganism species that
have been pretreated with and comprises a compound comprising a
transition metal ion that is reactive with an oxidative sterilant.
This pretreatment of the spores provides temporary "protection"
against the action of the oxidative sterilant for the purpose of
"slowing down" the effect of the oxidative sterilant on the
sterilization indicator, although not slowing down the effect of
the oxidative sterilant on the load under treatment in the
sterilization process. As noted above, the present invention is
intended to provide a better estimate of the efficacy of the
sterilization treatment by extending the time required to kill all
the microorganism spores in the sterilization indicator, further
into the sterilization process. The present invention thus is able
to offset the rapidity with which the oxidative sterilants act upon
conventional sterilization indicators, and thereby improve over
them.
EXAMPLES
[0047] Test results using both of these chemicals in the
resuspension of spores for use in biological indicators are
provided in the following Examples.
Example 1
Geobacillus stearothermophilus Spores Resuspended in Potassium
Ferricyanide
[0048] Geobacillus stearothermophilus spores are resuspended in
potassium ferricyanide concentrations ranging from 0.5 .mu.g/ml to
200 mg/ml in samples having a spore concentration of 1 E8 per ml
(1.times.10.sup.8 spores per milliliter). SCBI vials are inoculated
with 20 .mu.l (.apprxeq.2 million spores) of each of the sample
suspensions and air dried at least overnight. The SCBIs are then
capped and run in a VHP BIER vessel for the times shown in Table 1
below using a 0.8 g injection of 59% hydrogen peroxide. Table 1
shows the grow out results for the samples tested. Comparison of
the grow out results of the SCBIs containing additives with the
controls demonstrates that the additives have significantly
increased the resistance of the biological indicator system.
TABLE-US-00001 TABLE 1 Grow out results for SCBIs with potassium
ferricyanide Exposure Time (min.) 0.75 1 16 Sample Killed/Total
Samples Control (no additive) 20/40 21/38 19/19 Potassium 200 mg/ml
0/10 0/10 0/10 ferricyanide 25 mg/ml 0/10 0/10 0/10
(K.sub.3[Fe(CN).sub.6]) 15 mg/ml -- -- 0/10 5 mg/ml -- -- 0/10 100
.mu.g/ml -- -- 5/10* 10 .mu.g/ml -- -- 9/10 5 .mu.g/ml 0/10 3/10*
9/10 1 .mu.g/ml 0/10 2/10* 8/10* 0.5 .mu.g/ml 0/10 3/10* 7/10*
*NOTE: Individual values in the reported results may vary up or
down slightly but an overall trend is shown that indicates that as
the concentration of potassium ferricyanide used goes up, the
number of survivors also goes up.
[0049] As can be seen in the data in Table 1, half or more of the
indicator spores are killed in the control set in as little as 0.75
minutes, and after 16 minutes there are no survivors at all.
However, with as little as 100 .mu.g/ml of the added ferricyanide
half of the exposed spores survive a full 16 minutes of exposure.
Correspondingly less is required (0.5 to 5 .mu.g/ml) to reduce the
kill rate observed for the control set at 1 minute of exposure
(21/38) to less than 50%. Any of the tested amounts of ferricyanide
are sufficient to eliminate all spore kill at 0.75 minutes even
though half are killed in the set not treated with
ferricyanide.
Example 2
Geobacillus stearothermophilus Spores Resuspended in Prussian
Blue
[0050] Geobacillus stearothermophilus spores are resuspended in
Prussian blue concentrations ranging from 0.5 .mu.g/ml to 123 mg/ml
at a spore concentration of 1 E8 per ml. SCBI vials are inoculated
with 20 .mu.l million spores) of the appropriate suspension and air
dried at least overnight. The SCBIs are then capped and run in a
VHF) BIER vessel for the times listed below using a 0.8 g injection
of 59% hydrogen peroxide. Table 2 shows the grow out results for
the samples tested. Comparison of the grow out results of the SCBIs
containing additives with the controls demonstrates that the
additives significantly increase the resistance of the system.
TABLE-US-00002 TABLE 2 Grow out results for SCBIs with Prussian
blue. Exposure Time (min.) 0.75 1 16 Sample Killed/Total Samples
Control (no additive) 20/40 21/38 19/19 Prussian Blue 123 mg/ml
0/10 0/10 0/10 (Fe.sub.7(CN).sub.18) 25 mg/ml 0/10 0/10 0/10 15
mg/ml -- -- 0/10 5 mg/ml -- -- 0/10 100 .mu.g/ml -- -- 8/10 10
.mu.g/ml -- -- 8/10 5 .mu.g/ml 0/10 3/10 7/10* 1 .mu.g/ml 0/10
1/10* 6/10* 0.5 .mu.g/ml 0/10 2/10* 10/10 *NOTE: Individual values
may vary up or down slightly but an overall trend is shown that
indicates that as the concentration of Prussian blue used goes up,
the number of survivors also goes up.
As can be seen from Table 2, comparable results are obtained for
Prussian blue as compared to results obtained for potassium
ferricyanide (Table 1), indicating that these iron-containing
compounds are effective to retard the kill rate of vaporous
hydrogen peroxide and thus extend survivability (and the ability of
treated spores to monitor performance) much further into standard
hydrogen peroxide cycles.
[0051] The two agents exemplified above (potassium ferricyanide and
Prussian blue, although preferred, are not the only compounds that
can be used to degrade oxidizing sterilants.
[0052] An important advantage of the present invention is the
ability to "tune in" or "set" the resistance of a biological
indicator to oxidative sterilants by changing only the
concentration of the additives in the solution used to resuspend
the spores. This eliminates the need for multiple sporulation
methods required to achieve different spore resistance
characteristics/profiles or different molds for physically changing
the resistance characteristics of SCBI containers. In the present
invention biocompatible chemical additives that decompose the
oxidative sterilant to sub-components that are un-reactive towards
spores are used in order to increase, lengthen and modify the
resistance of a biological indicator. Because these modifications
are concentration dependent, this provides an unprecedented control
of post propagation spore crops that can be used over a broad range
of oxidative sterilant cycle conditions.
[0053] While the principles of the invention have been explained in
relation to certain particular embodiments, these embodiments are
provided for purposes of illustration. It is to be understood that
various modifications thereof will become apparent to those skilled
in the art upon reading the specification. Therefore, it is to be
understood that the invention disclosed herein is intended to cover
such modifications as fall within the scope of the appended claims.
The scope of the invention is limited only by the scope of the
claims.
* * * * *