Free AP-MICRO Laboratory Operations and Safety Questions and Answers 1 — Questions and Answers
Question 1: A new trainee in a microbiology laboratory is observed performing several tasks. Which of the following actions requires immediate correction by the training supervisor due to the significant risk of creating infectious aerosols?
- Forcefully expelling the last drop of liquid from a pipette into a culture medium. (Correct answer)
- Gently mixing a capped tube of broth culture on a vortex mixer.
- Using a sterile loop to transfer colonies from an agar plate to a broth tube.
- Taping a culture plate shut before placing it in the incubator.
Correct answer: Forcefully expelling the last drop of liquid from a pipette into a culture medium.
Forcefully expelling the last drop from a pipette is a common source of aerosol production in the laboratory. This action can create a spray of microscopic droplets containing microorganisms, which can then be inhaled by laboratory personnel or contaminate surfaces. Proper pipetting technique involves gently touching the tip to the side of the container to release the liquid without bubbling or forceful discharge.
Question 2: A reference laboratory needs to ship a pure culture of *Bacillus anthracis* to the CDC for further testing. According to IATA/DOT shipping regulations, this organism must be classified and shipped as:
- An exempt patient specimen.
- A Category A Infectious Substance, UN 2814. (Correct answer)
- A Category B Infectious Substance, UN 3373.
- Biological product, n.o.s.
Correct answer: A Category A Infectious Substance, UN 2814.
*Bacillus anthracis* is a high-consequence pathogen capable of causing life-threatening disease. It is explicitly listed as a Category A Infectious Substance, which includes organisms that can cause permanent disability or life-threatening disease in otherwise healthy humans. The proper shipping name is "Infectious substance, affecting humans," and it is assigned the identification number UN 2814. Category B (UN 3373) is for substances not meeting the Category A criteria.
Question 3: A technologist accidentally drops and breaks a flask containing a liquid culture of *Mycobacterium tuberculosis* outside the biosafety cabinet. Which of the following is the most critical first step in the cleanup procedure?
- Immediately wipe up the spill with paper towels and discard in the regular trash.
- Cover the spill with paper towels and carefully pour 70% ethanol over them.
- Alert others, vacate the area immediately, and prevent re-entry for at least 30 minutes. (Correct answer)
- Pour concentrated bleach directly onto the spill and let it sit for 5 minutes.
Correct answer: Alert others, vacate the area immediately, and prevent re-entry for at least 30 minutes.
For a spill involving a BSL-3 agent like *Mycobacterium tuberculosis*, the primary immediate risk is inhalation of infectious aerosols. The correct first action is to alert everyone, evacuate the area, and close it off for a period (e.g., 30-60 minutes) to allow aerosols to settle before trained personnel with appropriate PPE begin decontamination, typically using a tuberculocidal disinfectant.
Question 4: A technologist needs to subculture a mold isolate that is highly suspicious for *Coccidioides immitis*. To minimize the risk of laboratory-acquired infection, this work must be performed in which of the following?
- A chemical fume hood.
- A horizontal laminar flow clean bench.
- On an open bench with a respirator.
- A Class II Biosafety Cabinet. (Correct answer)
Correct answer: A Class II Biosafety Cabinet.
*Coccidioides immitis* is a Biosafety Level 3 (BSL-3) pathogen when manipulated in its mold form due to the high risk of aerosolizing infectious arthroconidia. All manipulations that could generate aerosols must be performed in a certified Class II Biosafety Cabinet (BSC), which provides personnel, environmental, and product protection. A chemical fume hood only protects the user from chemical vapors, and a laminar flow bench blows air toward the user, offering no personal protection.
Question 5: Which set of parameters is most commonly used for routine steam sterilization of microbiological media and decontamination of biohazardous waste in an autoclave?
- 121°C for 15 minutes at 15 psi. (Correct answer)
- 100°C for 30 minutes at 5 psi.
- 134°C for 5 minutes at 30 psi.
- 160°C for 2 hours (dry heat).
Correct answer: 121°C for 15 minutes at 15 psi.
The standard and most widely accepted conditions for steam sterilization (autoclaving) are 121°C for a minimum of 15 minutes at 15 pounds per square inch (psi) of pressure. This combination of moist heat and pressure is effective at killing even the most heat-resistant bacterial endospores, ensuring sterility.
Question 6: A laboratory technologist is preparing a disinfectant solution for the daily cleaning of a countertop where routine bacterial cultures are processed. What is the recommended dilution of household bleach (5.25-6.25% sodium hypochlorite) for use as a general-purpose laboratory disinfectant?
- 1:100 dilution
- Undiluted
- 1:50 dilution
- 1:10 dilution (Correct answer)
Correct answer: 1:10 dilution
A 1:10 dilution of standard household bleach provides a final concentration of approximately 0.5% (or 5000 ppm) sodium hypochlorite. This is the concentration widely recommended by agencies like the CDC for disinfecting surfaces in clinical and laboratory settings, as it is effective against a wide range of bacteria, viruses, and fungi.
Free AP-MICRO Laboratory Operations and Safety Questions and Answers 1
A new trainee in a microbiology laboratory is observed performing several tasks.
Which of the following actions requires immediate correction by the training supervisor due to the significant risk of creating infectious aerosols?