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 autoclave parameter is most critical for ensuring sterilization of a dense load of laboratory media?
Answer: Correct combination of temperature, time, and steam penetration
Effective sterilization requires moist heat (steam) to penetrate the entire load at the correct temperature (121°C) for sufficient time (≥15 min), as failure of any parameter can leave viable spores.
A microbiologist observes unexpected growth on a control plate that received no inoculum. This finding most likely indicates:
Answer: Contamination during preparation or plating
Growth on an uninoculated control plate indicates contamination occurred during media preparation, pouring, or plate handling, compromising experimental validity.
What is the purpose of a splash guard or shield when working with concentrated acids used in microbiological staining procedures?
Answer: To prevent aerosol and splash exposure to face and eyes
Splash guards and face shields protect mucous membranes from chemical splashes and aerosols generated when handling corrosive reagents like concentrated sulfuric or hydrochloric acid.
Which sterilization method is most appropriate for heat-labile solutions such as antibiotic stocks used in microbiology?
Answer: Filtration through a 0.22 μm membrane
Filtration through a 0.22 μm membrane physically removes bacteria and larger particles without heat, preserving the activity of heat-sensitive compounds like antibiotics.
In a Gram stain procedure, what is the role of iodine (Gram's iodine)?
Answer: Mordant that fixes crystal violet into the peptidoglycan layer
Gram's iodine acts as a mordant, forming a crystal violet–iodine complex that becomes trapped within the thick peptidoglycan layer of Gram-positive cell walls.
When pipetting a potentially infectious sample, the safest technique to avoid aerosol generation is:
Answer: Using mechanical pipette aids and working inside a BSC
Mechanical pipetting devices (never mouth pipetting) combined with working inside a biosafety cabinet minimize aerosol generation and exposure to infectious materials.
A researcher is working with a human pathogen classified at BSL-3. Which additional safety measure distinguishes BSL-3 from BSL-2 laboratories?
Answer: All procedures performed in a certified Class II or Class III BSC with directional airflow and controlled access
BSL-3 requires all manipulations of infectious materials inside certified BSCs, sustained directional airflow into the lab, and controlled access — requirements not mandatory at BSL-2.