Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving viable micro-organism
Reexamination Certificate
2001-12-06
2003-05-20
Redding, David A. (Department: 1744)
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving viable micro-organism
C435S287400, C435S810000
Reexamination Certificate
active
06566090
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to sterilization indicators for use in monitoring the effectiveness of sterilization procedures that use liquid sterilants, and in particular to sterilization indicators for use in monitoring the effectiveness of sterilization procedures that use liquid peracetic acid as a sterilant.
BACKGROUND OF THE INVENTION
In hospitals, industry and research it is necessary to sterilize certain articles, such as glassware, medical instruments and the like, to ensure that they are completely free of contamination by microorganisms that are capable of causing infection and disease. For example, it is well known that surgical instruments must be sterilized before they may be used in a surgical operation. Articles are sterilized by placing them in a machine called a sterilizer and subjecting them to a sterilization procedure of a type that is generally recognized as being effective at killing microorganisms.
Many different types of sterilization procedures are known in the art. These procedures may be differentiated from each other based on the identity of the sterilant used in each to destroy contaminating microorganisms. Currently, the most widely used procedures employ steam or an antimicrobial gas as sterilants.
However, sterilization procedures have recently been developed that use liquid sterilants. In particular, sterilization procedures that use liquid peracetic acid as a sterilant have become increasingly popular of late because they may be used to sterilize articles that cannot withstand the high temperatures and pressures of steam sterilization. A liquid peracetic acid sterilization procedure is described in U.S. Pat. No. 5,077,008 (Kralovic).
Sterilization indicators are quality control devices that are included with every load of articles placed in a sterilizer to monitor the antimicrobial effectiveness of each procedure conducted by the sterilizer. The indicators determine whether or not a sterilization procedure was lethal to contaminating microorganisms in the load. Typically, in the event of sterilization failure the indicators provide a readily detectable signal—such as fluorescence, luminescence or a color change—indicating that contaminating microorganisms may have survived and that the articles in the load must be subjected to another sterilization cycle.
Sterilization indicators have been developed that are both rapid and accurate for monitoring steam and gas procedures. But until now, a critical shortcoming associated with the use of liquid sterilant procedures has been that sterilization indicators have not been available that meet the performance standards set for sterilization indicators used with steam or gas procedures. In general, sterilization indicators for use with liquid sterilants are neither as fast or as dependable as sterilization indicators developed for use with steam.
Effective sterilization indicators that are widely used to monitor steam and gas sterilization procedures include biological indicators, rapid readout biological indicators, and dual rapid readout biological indicators. With each of these types of sterilization indicators, the failure of a sterilization procedure is indicated by a detectable change in a biological specimen—either an enzyme, a microorganism or both—that is attached to a carrier substrate, such as filter paper. In theory all of these sterilization indicators should be just as effective with liquid sterilants as they are with steam or gas. However, in practice it is often the case that the biological specimen is washed off of the carrier material during the procedure, or the carrier material is degraded by the liquid sterilant, so that any results obtained are unreliable.
Biological indicators have heretofore been recognized in the art as providing an accurate and direct method for determining whether or not a sterilization procedure has been effective, for steam and gas. Biological indicators are sterilization indicators that monitor the effectiveness of a sterilization procedure by measuring the effect of the procedure on a population of test microorganisms included in the indicator. If a sterilization procedure fails to generate a condition in the sterilizer that is lethal to the test microorganisms, surviving cells are detectable following a period of incubation and growth.
The test microorganism used in a biological indicator is typically a microorganism that is several times more resistant to the sterilization procedure being monitored than any microorganism that would likely to be present due to natural contamination. Spores of a microorganism, such as a bacterium, fungus, or protozoan, are most commonly used as the test microorganisms in biological indicators because of their hardy resistance to sterilization procedures.
Bacillus stearothermpophilus
spores are preferred for use in biological indicators for monitoring steam sterilization procedures, while
Bacillus subtilis
spores are preferred for use in biological indicators for ethylene oxide gas procedures.
Many biological indicators currently in use are self-contained biological indicators, which include both a spore strip and growth medium in separate compartments within the same closed container. During a sterilization procedure, sterilant, either steam or gas, enters the container through a shielded vent and contacts the spores but does not contact the growth medium. The barrier between the separate compartments is then broken, and the growth medium and spores are combined and incubated. Typically, a pH indicator compound that changes color in response to spore outgrowth is included with the growth medium. If test spores survive the sterilization procedure and grow out during incubation, the growth medium changes color, providing a readily detectable signal that the sterilization procedure has failed. A major advantage of self-contained biological indicators is that they can be sterilized, incubated and read without ever opening the container and exposing its contents to potential contamination from microorganisms present in the environmental air.
A typical self-contained biological indicator is described in U.S. Pat. No. 3,661,717 (Nelson). The indicator includes a compressible outer tube having one open end, and a porous, protective material covering the open end that allows sterilant, but not bacteria, to enter and leave the tube. A sealed glass ampoule within the outer tube contains growth medium and a chemical compound that changes color in response to spore growth. The outer tube also contains a spore strip between the outer tube and the ampoule. During a sterilization procedure steam or gas sterilant enters the indicator through the cover material and contacts the spores on the spore strip. The glass ampoule is then crushed by squeezing the compressible walls of the outer tube, and the spores are combined with the growth media. The indicator is incubated for a prescribed period of time and observed for a color change indicating spore growth and sterilization failure.
Attempts have been made in the art to develop biological indicators that are suitable for use with liquid sterilants. U.S. Pat. No. 4,885,253 (Kralovic) discloses a biological indicator for use with liquid sterilants that includes a vial with a sealed compartment containing growth media and a vented cap that is capable of being moved from an open position in which sterilant may freely enter the vial to a closed position. A spore strip is disposed above the sealed compartment and is exposed to sterilant during the sterilization procedure. Afterwards, a cutter device attached to the inner surface of the cap severs the barrier separating the growth media from the rest of the compartment, causing the spore strip to drop into the growth media for incubation.
U.S. Pat. No. 5,736,355 (Dyke) discloses a biological indicator for use with liquid sterilants that includes a vial with a sealed compartment containing growth medium and a vented cap that moves from an open position in which sterilant can freely enter the container to a closed position. A dar
Witcher Kelvin J.
Woodson Lewis P.
Burtis John A.
Redding David A.
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