AP-Micro Microbiology: Laboratory Operations and Safety 2 — Questions and Answers
Question 1: Which biosafety cabinet (BSC) class provides personnel protection only and does NOT protect the product from contamination?
- Class I (Correct answer)
- Class II Type A2
- Class II Type B2
- Class III
Correct answer: Class I
Class I BSCs exhaust air through a HEPA filter to protect personnel and the environment but draw unfiltered room air over the work surface, offering no product protection.
Question 2: A technician must dispose of a culture plate containing a BSL-2 organism. What is the correct first step before placing it in the biohazard waste bag?
- Autoclave the plate at 121°C for at least 15 minutes (Correct answer)
- Spray the plate surface with 70% ethanol
- Seal the plate with Parafilm and label it
- Place it directly in a sharps container
Correct answer: Autoclave the plate at 121°C for at least 15 minutes
BSL-2 biological waste must be autoclaved (decontaminated) before disposal to render the organisms non-viable.
Question 3: When calibrating a micropipette, which technique produces the most accurate volume delivery for aqueous solutions?
- Forward pipetting
- Reverse pipetting
- Air displacement with a pre-wet tip (Correct answer)
- Positive displacement
Correct answer: Air displacement with a pre-wet tip
Pre-wetting the tip with the solution before aspirating the target volume reduces error caused by vapor pressure and minimizes loss on tip walls, improving accuracy for aqueous samples.
Question 4: The use of personal protective equipment (PPE) is governed by the hierarchy of controls. Where does PPE fall in this hierarchy?
- Elimination
- Engineering controls
- Administrative controls
- Last line of defense (Correct answer)
Correct answer: Last line of defense
PPE is the last line of defense in the hierarchy of controls, used when elimination, substitution, engineering, and administrative controls cannot adequately reduce risk.
Question 5: A researcher accidentally spills a small volume of a BSL-2 culture on the bench. What is the correct immediate action?
- Cover with paper towels soaked in 10% bleach for 20 minutes, then clean up (Correct answer)
- Immediately wipe up with dry paper towels and discard
- Turn on the UV lamp for 30 minutes to decontaminate the area
- Evacuate the lab and call emergency services
Correct answer: Cover with paper towels soaked in 10% bleach for 20 minutes, then clean up
A 10% bleach (hypochlorite) solution applied for at least 20 minutes effectively disinfects BSL-2 spills before physical clean-up.
Question 6: Which type of culture media allows any organism to grow without providing any selective advantage or differential characteristic?
- Selective media
- Differential media
- General-purpose (non-selective) media (Correct answer)
- Enrichment media
Correct answer: General-purpose (non-selective) media
General-purpose or non-selective media such as nutrient agar or tryptic soy agar support the growth of a wide variety of organisms without selecting for or distinguishing between them.
Question 7: During an aseptic transfer, why must the loop or needle be flamed to red-hot before and after each transfer?
- To sterilize the loop and prevent cross-contamination between cultures (Correct answer)
- To activate the growth factors on the loop surface
- To ensure the agar surface is dry before inoculation
- To destroy the handle plastic to prevent reuse
Correct answer: To sterilize the loop and prevent cross-contamination between cultures
Flaming to red-hot incincerates any residual organisms on the loop, ensuring sterility before inoculation and preventing contamination of stock cultures after use.
AP-Micro Microbiology: Laboratory Operations and Safety 2
Which biosafety cabinet (BSC) class provides personnel protection only and does NOT protect the product from contamination?