The biologic standard used to test the efficiency of sterilization typically
involves the use of spores of a harmless bacillus. This method is widely
recognized in the scientific community and is based on the principle that if a
sterilization process can effectively destroy the most heat-resistant
microorganisms, it is assumed to be capable of killing all other less resistant
microbes.
The choice of using spores of a harmless bacillus is rooted in the fact that
bacterial spores are the most heat-resistant forms of microbial life. Spores are
metabolically inactive, which makes them very hardy and capable of surviving in
adverse environmental conditions for extended periods. For sterilization
validation, scientists often employ a biological indicator that contains spores
of a known heat-resistant bacterium, such as Geobacillus stearothermophilus
(formerly Bacillus stearothermophilus) or Bacillus subtilis. These organisms are
chosen because they have well-characterized resistance profiles, and their
destruction indicates that the sterilization process has achieved the necessary
lethality to eradicate all microbial life forms, including vegetative bacteria,
fungi, and viruses.
Let's examine the other options provided:
1. Spores of Clostridium tetani: While C. tetani is a spore-forming bacterium,
its spores are not commonly used as a biological indicator for sterilization
efficiency. C. tetani is a pathogen that causes tetanus, a serious disease.
However, it is not typically used for this purpose because there are safer and
more universally accepted biological indicators available.
2. Streptococcus pneumoniae: S. pneumoniae is a bacterium that can cause
pneumonia and other infections, but it is not a spore-former. Moreover, it is
generally less resistant to heat and sterilization methods compared to
spore-forming bacteria. Thus, it is not suitable as a standard for testing
sterilization efficiency.
3. Spores of a harmless bacillus: As previously mentioned, this is the most
appropriate choice for a biologic standard in sterilization testing. These
spores serve as reliable and safe indicators of sterilization efficacy because
they mimic the resistance of pathogenic spores without posing the actual risk of
infection.
4. Infectious hepatitis virus: While viruses can be highly resistant to some
sterilization methods, they are generally more sensitive to heat than bacterial
spores. Moreover, using infectious viruses as biological indicators poses
significant biosafety risks and is not a standard practice in routine
sterilization testing. For viral resistance testing, specific viruses or
virus-like particles may be used, but these are not typically employed as the
primary biological indicators for sterilization validation due to the complexity
and high containment requirements of such testing.
