Question 1

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

Accepted Answer

Sterilization removes all living microbes, while disinfection only kills pathogenic microbes.

Question 2

A hospital uses an autoclave to sterilize surgical instruments. What are the standard parameters for effective autoclaving?

Accepted Answer

$$15$$ $$lbs/in^2$$ pressure, $$121.5^\circ C$$ temperature, $$15$$ minutes$$

Question 3

Which of the following is the primary reason why 100% ethanol is less effective as a disinfectant than 70% ethanol?

Accepted Answer

100% ethanol does not penetrate cell membranes as well as 70% ethanol.

Question 4

A bacterium that grows optimally at $$37^\circ C$$ but can survive between $$20^\circ C$$ and $$45^\circ C is $$classified as a:

Accepted Answer

Mesophile

Question 5

Which of the following statements about halophiles is correct?

Accepted Answer

Halophiles grow optimally at high salt concentrations by keeping their cytoplasmic solute concentration high.

Question 6

Which enzyme is responsible for converting superoxide radicals ($$O_2$$^-$$) into hydrogen peroxide (H_2O_2$) and oxygen (O_2$) in aerobic bacteria?

Accepted Answer

Superoxide dismutase

Question 7

A patient is treated with penicillin for a bacterial infection. What is the primary mechanism by which penicillin acts?

Accepted Answer

Disrupts cell wall synthesis by preventing cross-linkage of NAM subunits

Question 8

Which of the following best explains why sulfonamides are selectively toxic to bacteria but not to humans?

Accepted Answer

Sulfonamides inhibit folic acid synthesis, which humans obtain from their diet.

Question 9

Which of the following is NOT a mechanism by which bacteria can acquire antibiotic resistance?

Accepted Answer

Inhibition of protein synthesis by aminoglycosides

Question 10

A microbiologist is using a HEPA filter in a laboratory. What is the minimum particle size that a HEPA filter can remove with over 99% efficiency?

Accepted Answer

$$0.3$$ microns

Question 11

Which of the following physical methods is most appropriate for sterilizing heat-sensitive liquids such as certain pharmaceuticals?

Accepted Answer

Membrane filtration

Question 12

Which of the following best describes the effect of ultraviolet (UV) light on microbial DNA?

Accepted Answer

UV light causes adjacent thymine bases to dimerize, disrupting DNA replication.

Question 13

Which of the following is the most resistant to chemical and physical methods of microbial control?

Accepted Answer

Prions

Question 14

A food scientist is designing a process to reduce microbial contamination in milk without significantly altering its taste. Which method should be used?

Accepted Answer

Flash pasteurization at $$71.6^\circ C$$ for $$15$$ seconds

Question 15

Which of the following best explains why hydrogen peroxide is not recommended for use on open wounds?

Accepted Answer

Hydrogen peroxide is rapidly broken down by catalase in human tissues.

Question 16

Which of the following best describes the action of heavy metals such as silver and mercury on microbes?

Accepted Answer

They denature proteins by reacting with sulfhydryl groups.

Question 17

A bacterium is classified as a facultative anaerobe. Which of the following best describes its growth pattern in thioglycollate broth?

Accepted Answer

Growth occurs throughout the tube, but is denser at the top where oxygen is present.

Question 18

Which of the following is a correct example of selective toxicity in antimicrobial therapy?

Accepted Answer

A drug that inhibits peptidoglycan synthesis in bacteria but does not affect human cells.

Question 19

Which of the following best explains why pickling is an effective method of food preservation?

Accepted Answer

Pickling creates a hypertonic environment that causes plasmolysis in most bacteria.

Microbial Control: Physical and Chemical Methods, Growth Limits, and Chemotherapy

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