Question 1

Which of the following best describes a complex culture medium?

Accepted Answer

A medium composed of digests of microbial, animal, or plant products, with composition varying from batch to batch.

Question 2

A microbiologist wants to grow a fastidious microorganism that requires additional nutrients. Which type of medium should be used?

Accepted Answer

Enriched medium

Question 3

Which of the following statements about Mannitol Salt Agar (MSA) is correct?

Accepted Answer

It is both a selective and differential medium.

Question 4

A scientist is measuring the optical density (OD) of a bacterial culture using a spectrophotometer. What is the main limitation of this method?

Accepted Answer

It cannot distinguish between living and dead cells.

Question 5

Which method would be most appropriate for quantifying viable bacteria in a water sample with a low cell count?

Accepted Answer

Membrane filtration

Question 6

Which of the following best describes the decimal reduction time ($$D-$$value) in microbial control?

Accepted Answer

The time required for a 10-fold (1-log) reduction in the microbial population at a given temperature.

Question 7

Which physical method of microbial control is most effective for sterilizing heat-sensitive solutions?

Accepted Answer

Filtration using a 0.2 $$\mum $$membrane

Question 8

A hospital technician needs to sterilize surgical instruments. Which method should be used to ensure destruction of all microorganisms, including endospores?

Accepted Answer

Autoclaving at 121 $$^\circC$$, 15 PSI for 10-15 minutes

Question 9

Which of the following statements about UV radiation as a microbial control method is correct?

Accepted Answer

It is effective for surface sterilization by inducing thymine dimers in DNA.

Question 10

A laboratory is testing the effectiveness of a new disinfectant. Which assay would best determine the minimum concentration needed to inhibit bacterial growth?

Accepted Answer

Minimum inhibitory concentration (MIC) assay

Question 11

Which of the following is the correct order of microbial resistance to chemical agents, from most resistant to least resistant?

Accepted Answer

Prions \u003e Endospores \u003e Mycobacteria \u003e Gram-negative bacteria \u003e Enveloped viruses

Question 12

Which of the following best describes the action of an alkylating agent as a chemical disinfectant?

Accepted Answer

It modifies DNA, leading to failure in replication and protein synthesis.

Question 13

A researcher is using a Petroff–Hausser counting chamber to count bacteria. What is being measured?

Accepted Answer

Total cell count (living and dead)

Question 14

Which of the following statements about bacteriostatic agents is correct?

Accepted Answer

They inhibit bacterial growth, but cells can resume growth if the agent is removed.

Question 15

A sample is diluted and plated using the spread plate method. After incubation, 45 colonies are counted on a plate inoculated with 0.1 mL of a $$10^{-4}$$ dilution. What is the original concentration of bacteria in the sample (CFU/mL)?

Accepted Answer

$$4.5 	imes 10^6$ CFU/mL

Question 16

Which of the following is NOT a factor that influences the effectiveness of an antimicrobial agent?

Accepted Answer

Color of the microorganism

Question 17

Which method would be most appropriate for culturing obligate anaerobes?

Accepted Answer

Incubation in an anaerobic jar with a reducing agent

Question 18

Which of the following best describes the difference between sterilization and disinfection?

Accepted Answer

Sterilization kills all vegetative cells, endospores, and viruses, while disinfection reduces microbial load including pathogens.

Question 19

A laboratory is using the Kirby-Bauer diffusion test to evaluate antibiotics. What does the zone of inhibition around a disk indicate?

Accepted Answer

The effectiveness of the antibiotic against the test organism.

Cultivation and Control of Microbial Growth: Microbiology Study Guide

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