HSPA Biological and Chemical Indicators 1 — Questions and Answers
Question 1: What is the primary purpose of a biological indicator (BI) in sterilization monitoring?
- To measure the sterilizer's temperature accuracy
- To confirm that the sterilization process was lethal to highly resistant bacterial spores, providing the highest level of sterility assurance (Correct answer)
- To verify the wrapping material is sterilization-compatible
- To test the quality of the water supply
Correct answer: To confirm that the sterilization process was lethal to highly resistant bacterial spores, providing the highest level of sterility assurance
Biological indicators contain standardized populations of highly resistant bacterial spores that serve as the gold standard for verifying sterilization lethality. A negative result (no spore growth after incubation) demonstrates that conditions inside the sterilizer were sufficient to kill even the most resistant organisms, providing the highest assurance of sterility.
Question 2: Which organism is used as the biological indicator for steam sterilization?
- Escherichia coli
- Geobacillus stearothermophilus (Correct answer)
- Bacillus atrophaeus
- Staphylococcus aureus
Correct answer: Geobacillus stearothermophilus
Geobacillus stearothermophilus spores are used for steam sterilization because they are among the most resistant organisms to moist heat. Their high resistance to steam sterilization conditions makes them an appropriate challenge organism. If the sterilization process kills G. stearothermophilus spores, it will have killed all less resistant organisms.
Question 3: Which organism is used as the biological indicator for ethylene oxide (EtO) sterilization?
- Geobacillus stearothermophilus
- Bacillus atrophaeus (formerly B. subtilis var. niger) (Correct answer)
- Clostridium sporogenes
- Mycobacterium terrae
Correct answer: Bacillus atrophaeus (formerly B. subtilis var. niger)
Bacillus atrophaeus spores are used for EtO sterilization monitoring because they exhibit high resistance to ethylene oxide gas. Each sterilization modality uses a different challenge organism that is specifically resistant to that method's killing mechanism. This ensures the BI provides a valid challenge for the specific sterilization process.
Question 4: What is a Class 5 integrating chemical indicator?
- A simple process indicator that changes color upon exposure to sterilant
- An internal indicator that responds to all critical parameters of the sterilization cycle and correlates with biological indicator results at stated sterilization conditions (Correct answer)
- An external label that shows the item was processed
- A test strip that only measures temperature
Correct answer: An internal indicator that responds to all critical parameters of the sterilization cycle and correlates with biological indicator results at stated sterilization conditions
Class 5 integrating indicators are designed to react to all critical parameters of the sterilization process (time, temperature, and steam presence for steam sterilization) and their performance correlates with biological indicator kill at stated sterilization values. They provide the highest level of chemical indicator assurance, second only to biological indicators.
Question 5: What is the difference between a Class 1 and a Class 4 chemical indicator?
- They are identical in function
- Class 1 (process indicator) only distinguishes processed from unprocessed items, while Class 4 (multi-variable indicator) reacts to two or more critical sterilization parameters (Correct answer)
- Class 4 is placed outside the pack, Class 1 inside
- Class 1 monitors more parameters than Class 4
Correct answer: Class 1 (process indicator) only distinguishes processed from unprocessed items, while Class 4 (multi-variable indicator) reacts to two or more critical sterilization parameters
Class 1 indicators (like autoclave tape) simply show that an item was exposed to a sterilization process, helping prevent mix-ups between processed and unprocessed items. Class 4 multi-variable indicators react to two or more critical sterilization parameters, providing more specific information about whether adequate conditions were achieved.
Question 6: How often should biological indicators be used to monitor steam sterilizers?
- Only during annual inspections
- At least weekly, and with every load containing implantable devices (Correct answer)
- Once per month
- Only when a sterilization failure is suspected
Correct answer: At least weekly, and with every load containing implantable devices
AAMI ST79 recommends biological indicator testing at least weekly for routine loads and with every load containing implantable devices. Some facilities test every load for maximum assurance. For implants, BI results should be confirmed negative before the implants are released for patient use, unless there is a documented urgent clinical need.
HSPA Biological and Chemical Indicators 1
What is the primary purpose of a biological indicator (BI) in sterilization monitoring?