AP-Micro Microbiology: Sterilization, Disinfection, and Infection Control 1 — Questions and Answers
Question 1: Which sterilization method uses saturated steam under pressure to destroy all microorganisms, including bacterial endospores?
- Dry heat oven
- Autoclave (moist heat) (Correct answer)
- UV radiation
- Pasteurization
Correct answer: Autoclave (moist heat)
Autoclaving uses saturated steam at 121°C and 15 psi for 15–20 minutes, which is sufficient to denature proteins and kill all microbial life including heat-resistant spores.
Question 2: What are the standard conditions for gravity-displacement autoclave sterilization?
- 100°C for 30 minutes at ambient pressure
- 121°C for 15–20 minutes at 15 psi (Correct answer)
- 134°C for 60 minutes at 30 psi
- 160°C for 10 minutes at 15 psi
Correct answer: 121°C for 15–20 minutes at 15 psi
Standard gravity autoclaving requires 121°C, 15 psi, for a minimum of 15–20 minutes to ensure complete sterilization of wrapped instruments.
Question 3: Which sterilization method is most appropriate for heat-labile materials such as plastics, rubber tubing, and electronic components?
- Dry heat at 160°C
- Steam autoclave at 121°C
- Ethylene oxide (EtO) gas (Correct answer)
- Incineration
Correct answer: Ethylene oxide (EtO) gas
Ethylene oxide is a low-temperature (37–63°C) alkylating gas that sterilizes heat-sensitive materials without causing thermal damage.
Question 4: Dry heat sterilization of glassware and metal instruments typically requires which conditions?
- 100°C for 2 hours
- 121°C for 30 minutes
- 160°C for 1–2 hours (Correct answer)
- 250°C for 15 minutes
Correct answer: 160°C for 1–2 hours
Dry heat sterilization requires 160°C for 1–2 hours (or 170°C for 1 hour) because dry heat is less efficient than moist heat at penetrating and killing microorganisms.
Question 5: Which biological indicator is used to validate the effectiveness of steam autoclave sterilization cycles?
- Bacillus anthracis spores
- Geobacillus stearothermophilus spores (Correct answer)
- Bacillus subtilis var. niger spores
- Clostridium perfringens spores
Correct answer: Geobacillus stearothermophilus spores
Geobacillus stearothermophilus (formerly Bacillus stearothermophilus) produces highly heat-resistant spores that serve as the gold-standard biological indicator for autoclave validation.
Question 6: Which statement correctly describes a limitation of ethylene oxide (EtO) sterilization?
- It is ineffective against bacterial endospores
- Items must undergo a lengthy aeration period to remove toxic residues before use (Correct answer)
- It requires temperatures above 200°C to function
- It cannot be used on rubber or plastic materials
Correct answer: Items must undergo a lengthy aeration period to remove toxic residues before use
EtO leaves toxic residues on processed items, requiring an aeration period of several hours to days to off-gas before the items are safe for patient use.
Question 7: According to the Spaulding classification, a flexible gastrointestinal endoscope that contacts intact mucous membranes but does not penetrate sterile tissue is classified as 'semicritical' and requires:
- Full sterilization
- High-level disinfection (Correct answer)
- Intermediate-level disinfection
- Low-level disinfection
Correct answer: High-level disinfection
Semicritical items (those contacting mucous membranes or non-intact skin) require high-level disinfection, which eliminates all microorganisms except high numbers of bacterial spores.
AP-Micro Microbiology: Sterilization, Disinfection, and Infection Control 1
Which sterilization method uses saturated steam under pressure to destroy all microorganisms, including bacterial endospores?