AP-Micro Microbiology: Sterilization, Disinfection, and Infection Control 2 — Questions and Answers
Question 1: High-level disinfection is defined as a process that eliminates:
- Vegetative bacteria only
- All microorganisms except bacterial spores (Correct answer)
- All microorganisms including high numbers of bacterial spores
- Vegetative bacteria and lipid-enveloped viruses only
Correct answer: All microorganisms except bacterial spores
High-level disinfection kills all microorganisms except high numbers of bacterial endospores; sterilization is required to eliminate spores completely.
Question 2: Which chemical agent is classified as a high-level disinfectant and is commonly used for reprocessing heat-sensitive flexible endoscopes?
- Isopropyl alcohol 70%
- Quaternary ammonium compound (quat)
- Glutaraldehyde 2% (Correct answer)
- Phenolic compound
Correct answer: Glutaraldehyde 2%
2% glutaraldehyde (e.g., Cidex) is an aldehyde-based high-level disinfectant widely used for endoscope reprocessing when sterilization is not possible.
Question 3: Chlorine-based disinfectants such as sodium hypochlorite exert their antimicrobial activity primarily by:
- Disrupting the lipid bilayer of the cell membrane
- Oxidizing cellular components and denaturing proteins (Correct answer)
- Inhibiting peptidoglycan cross-linking in the cell wall
- Intercalating into microbial DNA to block replication
Correct answer: Oxidizing cellular components and denaturing proteins
Hypochlorite releases hypochlorous acid, a powerful oxidizer that destroys proteins, enzymes, and nucleic acids through oxidation, causing broad-spectrum microbial death.
Question 4: Which antiseptic is preferred for surgical hand scrubs and preoperative patient skin preparation due to its persistent residual antimicrobial activity?
- Isopropyl alcohol 70%
- Povidone-iodine 10%
- Chlorhexidine gluconate (Correct answer)
- Benzalkonium chloride
Correct answer: Chlorhexidine gluconate
Chlorhexidine gluconate binds to skin proteins and provides prolonged residual activity lasting several hours after application, making it preferred for surgical antisepsis.
Question 5: Quaternary ammonium compounds (quats) are LEAST effective against which category of microorganisms?
- Gram-positive vegetative bacteria
- Lipid-enveloped viruses
- Gram-negative vegetative bacteria on clean surfaces
- Mycobacteria and bacterial endospores (Correct answer)
Correct answer: Mycobacteria and bacterial endospores
Quats have low activity against mycobacteria and no sporicidal activity; their cationic surfactant mechanism is ineffective against the waxy mycobacterial cell wall and resistant endospores.
Question 6: The correct sequence for reprocessing contaminated reusable medical instruments before they are returned to service is:
- Sterilization → Disinfection → Cleaning
- Cleaning → Disinfection → Sterilization (Correct answer)
- Disinfection → Cleaning → Sterilization
- Cleaning → Sterilization → Disinfection
Correct answer: Cleaning → Disinfection → Sterilization
Cleaning must occur first to remove organic material that would otherwise protect microorganisms, followed by disinfection or sterilization as appropriate for the item's classification.
Question 7: Under the Spaulding classification, 'non-critical' items such as blood pressure cuffs and stethoscopes that contact only intact skin require which level of reprocessing?
- Sterilization
- High-level disinfection
- Intermediate or low-level disinfection (Correct answer)
- No reprocessing — wiping with a dry cloth is sufficient
Correct answer: Intermediate or low-level disinfection
Non-critical items contact only intact skin, which is a natural barrier to infection, so intermediate or low-level disinfection is sufficient per the Spaulding framework.
AP-Micro Microbiology: Sterilization, Disinfection, and Infection Control 2
High-level disinfection is defined as a process that eliminates: