US 3711378 A
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Jan. 16, 1973 K KERELUK MICROBIOLOGICAL-SCALED STERILITY CONTROLS Filed Sept. 15, 1969 Nm m .SLN
BY KARL /ERfL-UK aux /M AUM/var.
United States Patent O M MICROBIOLOGICAL-SCALED STERILITY CONTROLS Karl Kereluk, Fairview, Pa., assignor to American Sterilizer Company, Erie, Pa. Filed Sept. 15, 1969, Ser. No. 857,668 Int. Cl. C12k 1/04 U.S. Cl. 195--103.5 R 14 Claims ABSTRACT F THE DISCLOSURE A method and apparatus for determining the effectiveness of a sterilizing cycle by preparing a plurality for example seven spore impregnated strips of filter paper sealed in glassine envelopes and exposing the strips to the sterilizing Cycle under study. Each of the seven strips has a different spore population, e.g. 103, 104, 105, 106, 107, 1018, and 109. The sterility control is either exposed directly to the active elements of the sterilizing process or the control is placed in the load of materials to be sterilized. The strips are then removed and incubated and studied. The effectiveness of the cycle can be `concluded from the spore strip containing `the highest population on which the entire population is killed.
STATEMENT OF THE INVENTION This invention relates to sterility controls, and more particularly, to control devices for determining the effectiveness of a sterilizing cycle.
OBJECTS OF THE INVENTION It is an object of the invention to provide an improved sterility control.
Another object of the invention is to provide an improved control for determining the effectiveness of a sterilizing cycle.
Another object of the invention is to provide an improved structure of a sterility control.
Another object of the invention is to provide a sterility control, which is simple in construction, economical to manufacture, and simple and efliicient to use.
Another object of the invention is to provide an improved method of controlling a sterilizing process in a sterilizer.
GENERAL STATEMENT OF THE INVENTION It is well known in the field of sterilization that the sterility of an article or commodity is predicated in its exposure to fairly precise conditions which cannot be varied to any great extent without sacrificing sterility. In many cases, even slight variations in exposure conditions may result in so-called hits or misses or situations where sterility may be achieved on one occasion, fail on the next and succeed on the third attempt even though the test conditions were supposedly the same each time.
Because of these situations, a method is hereby proposed which enables an operator or manufacturer of sterile disposables to evaluate the effectiveness and/or eiciency of the sterilizing process. With this method, it is possible to determine (1) whether the conditions of the process are capable of achieving sterility, (2) whether the Iconditions of the process will achieve sterility each time the process is conducted, and (3) whether some safety factor, such as increased exposure time or increased temperature, should be considered in order to attain sterility and/or reproducibility of results.
DESCRIPTION OF THE PROCESS The proposed method is based on the use of specially prepared bacterial spore-impregnated strips of filter paper,
sealed in glassine envelopes and exposed'to the conditions of the sterilization process under study, and the proper interpretation of the test results.
The bacterial spore-impregnated strips, employed in this method, are prepared in a manner similar to currently used spore strips with one exception. A total of seven spore strips are prepared as a set with each strip containing a different concentration or population of bacterial spores, i.e., the first strip will contain a population of 1 10z bacterial spores, the second strip will contain a population of 1 103 spores, and so on until the final or seventh strip will contain a population of 1 108 bacterial spores.
The organism used in this method comprises albacterial sporeforming specie known to be resistant to the sterilizing process being used or tested. For example, the bacterial specie used to test the eiiiciency of a steam sterilizing proc'- ess is usually Bacillus stearothermophilus, while Bacillus subtilis var. niger is more commonly employed to test the efiiciency of such sterilizing processes as dry heat or ethylene oxide.
In practice, the microbiological-scaled sterility controls are exposed either directlyto the sterilization process or are placed in the load of materials to be sterilized. The sterilization process is conducted in the usual manner following which the sterility controls are removed from the sterilizing apparatus or the load, aseptically removed from their respective glassine envelopes and cultured in tubes of recommended bacteriological culture media. The tubes are then incubated at the optimum temperature of the test organism (usually stipulated on the glassine envelope) for a period of seven days. Results are recorded in terms of growth or no growth.
On the basis of the results, the effectiveness and/or efficiency of the sterilizing process under the conditions employed can be determined. To illustrate, in the event that the sterility `control strips covering spore populations ranging from 102 to 106 are sterilized but those strips containing 10'7 through 108 spores are not sterilized, it can be concluded that the sterilizing conditions used are capable of sterilizing materials containing microbial contamination levels up through 1 10 organisms. If successive tests produce the same result, it can be concluded that the conditions of the sterilizing process are reproducible and will provide consecutive sterilizing cycles. However, if the above results are not achieved in each successive cycle, it
can be concluded that the sterilizing conditions are not capable of producing reproducible results and will require some modification. If all seven of the lsterility control strips are repeatedly sterilized, it can be concluded that the sterilizing conditions are capablev of sterilizing materials or articles which are unusually heavily contaminated. How- EXAMPLE (1) Sterile carriers (Spordex strips and ceramic tiles) were inoculated with Varied spore populations (103, 104, 105, 106, 10", 10B, 109).
(2) They were exposed to 500 mg./l. of Eto 50% R.H. and F. at varied time intervals. The shortest period of exposure for the inoculated carriers was five minutes. The exposure period was increased -to 30 minutes by five-minute increments.
(3) At each exposure period for each of the seven populations 10 inoculated carriers were exposed (5 spordex strips, 5 ceramic tiles) to the test conditions. After exposure each carrier was transferred individually to a tube of Trypticase Soy Broth(TSB). The tubes were incubated at 37 C. for one week. Following incubation each tube of TSB with a carrier `was observed for the presence or absence of growth.
STATEMENT OF PRIOR ART Test strips have been used for various purposes to indicate various intensities of process, for example, Pat. 3,245,- S82.l discloses a test strip for testing the phenylalanine in blood.
FIG. 1 isfan isometric view of one embodiment of the invention.
FIG. 2 is a top view of another embodiment of the invention.
v FIG. 3 is a cross-sectional view taken on line 3 3 of FIG-2. f
FIG. 4 is a cross-sectional view taken on line 4--4 of FIG. 2.
FIG. 5 is aview showing the embodiment of FIG. v2 folded.
FIG. 6 is a view showing the embodiment of FIG. '2 formed into a roll.
Now with more particular reference to the embodimen of FIG. 2 through 6, the glassine envelopes are indicated at 10. They are divided into containers 11, 12, 13, l14, 15, 16, 17, and 18 by they scored lines 19, 20,21, 22, 23, and 24. The material which makes up the envelope may be made of a sheet which is folded back on itself at and sealed along lines 26 and 27 by a suitable process. A spore carrier 28 will be enclosed in each compartment of the envelope. The spore carrier 28 will be specially prepared bacterial spore impregnated strips of lter paper, sealed in the glassine envelopes, and they will be exposed to the condition of sterilizing by placing the envelope 10 either rolled up, as shown in FIG. 6, or folded, as shown in FIG. 5, or lying at as shown in FIG. 2.
Inthe embodiment of the invention shown in FIG. l a container 110 is shown, which is made of relatively rigid material and which has compartments 111, 112, 113, 114, 115, 116, 117. The compartments will each contain at least one bacterial sporey impregnated strip 118, 119, 120, 121, 122, 123, and 124. The strips will be made according to a well known process, such as for example shown in Pat. No. 2,931,757, and will be impregnated with different numbers of spores, for example, spore strips 118 through 124 will be impregnated with 1 1O2 bacterial spores, 1 103 bacterial spores, 1 104 bacterial spores, on through 1X1()8 bacterial spores, respectively.- A scored liner 126 .formed in the walls of the compartments, by which the upper` part 127 ofthe container may be removed. The spore strip may then be removed and incubated. The container 110 may be molded from a plastic material for example vinyl or polyethylene.
The'embodiments. of the invention in which an exclusive property or privilege is claimed are defined as follows: 1., A method of determining the etfectiveness of a sterilizing cycle comprising providing a set of at least seven spore carrying devices, each having a different sporev population, f
the numberv ofv spores in each said populationfbeing equal to a real positive integer greater than zero raised to a real positive exponential integer, each said exponential power being different from the others, exposing said set4 of devices to the sterilizing cycle, f incubating saidA devices and observing the devices having the highest population that is completely killed. 2, The;l method`reeitedin claim 1 wherein said devices are inoculated'y with at least 102, 103, 104, 105, 106,10, and 1,08' spores'respectively,
saidspores are inoculated` with spores taken from the group of Bacillus stearothermophilus and Bacillus .subtilis var. niger. f
3. The process recited in claim 2 wherein said spore devices are incubated after exposure.
4. A sterility control comprising a plurality of containers adapted to be disposed in a sterilizing chamber,
a spore carrier in each said container,
each said spore carrier being impregnated with a different population of spores,
the number of spores in each said population being equal to areal positive integer greater than zero raised to a real positive exponential integer, each said exponential power being different from the others, whereby the effectiveness of the cycle can be determined by observingsaid spore carrier having the largest number of said spores wherein all said spores are killed.
5; The control recited in claim 4 wherein said containers are connected together in edge to edge relation.
6. The control recited in claim S wherein said containers are inthe form of glassine envelopes.
7. The control recited in claim 6 wherein said envelopes are adapted to be disposed in said sterilzer in the form of a roll.
8. The control recited in claim l7 wherein at least seven l of said devices are provided in said containers.
y9. A container having at least seven separate compartments,
said compartments being isolated from each other,
a spore strip in each said compartment,
each said strip being impregnated with a different population of spores from the other strips, the number of spores in each said population being equal to a real positive integer greater than zero raised to a real positive exponential integer, each said exponential power being different froml the others,
said container with said spore strips being adapted to be placed in a sterilizing chamber during sterilizing cycle and said strips subsequently incubated and the strips having all spores thereon killed whereby the effectiveness of said cycle can be determined by observing the said strip having the largest number of said spores wherein all said spores are killed.
10. The control recited in claim 9 wherein said compartments are generally rectangular incross section.
11. The control recited in claim 9-whe1'ein said containers are in the form of glassine envelopes, and a removable cover on each envelope,
said envelope being scored along a line adjacent on edge whereby the covercan be removed.
12. The control recited in claim 9vwherein said con tainer is scored adjacent one edge whereby said covermay be removed and said container isV made in the form of glassineenvelopes attached together..
13. The control recited in claim 9 wherein said container is made of a relatively rigid material.. l
14. vThe control recited in claim 13 wherein said container is made. from a material taken from the groupv of vinyland polyethylene. 1`
References Cited UNITED STATES'PATENTS.
5/1960 Rdzok et al. 195-103.5
OTHER REFERENCES Brewer et al.: 1. Pharm. Sci. 50117142 (1961).
A. LOUIS MONACELL,` Primary Examiner M. D. HENSLEY, Assistant Examiner U.S. Cl. XR.