AP-Micro Microbiology: Laboratory Operations and Safety 3

Question 1

Which autoclave parameter is most critical for ensuring sterilization of a dense load of laboratory media?

Accepted Answer

Correct combination of temperature, time, and steam penetration

Answer

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.

Question 2

A microbiologist observes unexpected growth on a control plate that received no inoculum. This finding most likely indicates:

Accepted Answer

Contamination during preparation or plating

Answer

Growth on an uninoculated control plate indicates contamination occurred during media preparation, pouring, or plate handling, compromising experimental validity.

Question 3

What is the purpose of a splash guard or shield when working with concentrated acids used in microbiological staining procedures?

Accepted Answer

To prevent aerosol and splash exposure to face and eyes

Answer

Splash guards and face shields protect mucous membranes from chemical splashes and aerosols generated when handling corrosive reagents like concentrated sulfuric or hydrochloric acid.

Question 4

Which sterilization method is most appropriate for heat-labile solutions such as antibiotic stocks used in microbiology?

Accepted Answer

Filtration through a 0.22 μm membrane

Answer

Filtration through a 0.22 μm membrane physically removes bacteria and larger particles without heat, preserving the activity of heat-sensitive compounds like antibiotics.

Question 5

In a Gram stain procedure, what is the role of iodine (Gram's iodine)?

Accepted Answer

Mordant that fixes crystal violet into the peptidoglycan layer

Answer

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.

AP Practice Test

AP Practice Test

AP-Micro Microbiology: Laboratory Operations and Safety 3