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Biological indicators are the only process
indicators that directly monitor the lethality of a given
sterilization process. Spores used to monitor a sterilization
process have demonstrated resistance to the sterilizing agent and
are more resistant than the
bioburden
found on medical devices. While
Bacillus atrophaeus
spores are used to monitor ETO and dry
heat sterilizers, Geobacillus stearothermophilus spores are used to
monitor steam sterilization, hydrogen peroxide gas plasma, and
liquid peracetic acid sterilizers. Geobacillus stearothermophilus
spores are incubated at 55-60°C and Bacillus atrophaeus spores are
incubated at 35-37°C.
Weekly testing is minimum:
Steam and low temperature sterilizers
(e.g., hydrogen peroxide gas plasma, peracetic acid) should be
monitored at least weekly with the appropriate commercial
preparation of Geobacillus stearothermophilus spores. If a
sterilizer is used frequently (e.g., several loads per day), daily
use of biological indicators allows earlier discovery of
equipment
malfunctions or procedural errors and thus minimizes the extent of
patient surveillance and product recall needed in the event of a
positive biological indicator. Each load should be monitored if it
contains implantable objects. If feasible, implantable items should
not be used until the results of spore tests are known to be
negative.
See also
www.cdc.gov/oralhealth/infectioncontrol/faq/sterilization_monitoring.htm
Originally, spore-strip biological indicators required up to 7 days
of incubation to detect viable spores from marginal cycles (i.e.,
when few spores remained viable). The next generation of
biological indicator was
self-contained in plastic vials containing a spore-coated paper
strip and a growth media in a crushable glass ampoule. This
indicator had a maximum incubation of 48 hours but significant
failures could be detected in ≤24 hours. A rapid-readout biological
indicator that detects the presence of enzymes of Geobacillus
stearothermophilus by reading a fluorescent product produced by the
enzymatic breakdown of a non-fluorescent substrate has been marketed
for the more than 10 years. Studies demonstrate that the sensitivity
of rapid-readout tests for steam sterilization (1 hour for 132°C
gravity sterilizers, 3 hrs for
121°C gravity and 132°C
vacuum
sterilizers) parallels that of the conventional
sterilization-specific biological indicators and the fluorescent
rapid readout results reliably predict 24 and 48-hour and 7-day
growth. The rapid-readout biological indicator is a dual indicator
system as it also detects acid metabolites produced during growth of
the Geobacillus stearothermophilus spores. This system is different
from the indicator system consisting of an enzyme system of
bacterial origin without spores. Independent comparative data using
suboptimal sterilization cycles (e.g., reduced time or temperature)
with the enzyme-based indicator system have not been published. ATS,
Inc. also has a rapid readout system available – see
Biological Indicators.
ATS, Inc. facilitates high quality and stringent laboratory
standards with our
Mail-In Services.
We provide a dual-spore strip inoculated with both spores;
Geobacillus stearothermophilus and Bacillus atrophaeus spores,
allowing users to spore test all sterilizers used in healthcare
facilities.
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