Microbiology: Laboratory Operations and Safety Flashcards
7 cards from real AP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Microbiology: Laboratory Operations and Safety flashcards as text
Which personal protective equipment is specifically required when handling formaldehyde-fixed specimens during histological processing in a microbiology lab?
Answer: Chemical splash goggles, nitrile gloves, and a lab coat — with work performed in a fume hood
Formaldehyde is a volatile carcinogen and respiratory irritant; chemical splash goggles, nitrile gloves, a lab coat, and a fume hood are all required to minimize dermal, ocular, and inhalation exposure.
What is the minimum time required for dry heat sterilization of glassware at 160°C in a hot-air oven?
Answer: 2 hours
Dry heat sterilization at 160°C requires at least 2 hours because dry heat transfers energy less efficiently than moist heat, requiring longer exposure to destroy all microbial life including endospores.
A culture of E. coli is grown to OD₆₀₀ = 0.8. A researcher doubles the volume by adding sterile broth. What happens to the OD₆₀₀ reading immediately after mixing?
Answer: It drops to approximately 0.4 because the cell concentration is halved
Optical density is directly proportional to cell concentration; doubling the volume halves the concentration, so OD₆₀₀ drops from 0.8 to approximately 0.4.
Which of the following is NOT a valid reason to use a negative-pressure room for BSL-3 pathogen work?
Answer: To protect workers inside from pathogens carried in from outside
Negative pressure keeps air flowing INTO the lab (inward), preventing escape of pathogens — it does not protect workers from outside air; that role belongs to BSCs and PPE.
When performing a wet mount preparation for direct microscopic examination of a sample, the coverslip should be:
Answer: Lowered at an angle to minimize bubble formation, then gently pressed
Lowering the coverslip at an angle allows air to escape gradually, reducing bubble formation that would obscure organism visualization without crushing motile organisms.
A sharp contaminated needle must be disposed of immediately after use. Which action is correct?
Answer: Place the uncapped needle directly into an approved puncture-resistant sharps container
Uncapped needles must go directly into a puncture-resistant sharps container; two-handed recapping is prohibited because it is a leading cause of needlestick injuries.
What is the function of a catalase test in the clinical microbiology laboratory?
Answer: Detects the enzyme that converts H₂O₂ to water and oxygen, used to differentiate Staphylococcus (positive) from Streptococcus (negative)
The catalase test detects bubbling when H₂O₂ is added; Staphylococci are catalase-positive while Streptococci are catalase-negative, making it a rapid initial differential test.