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 best explains why 100% ethanol is less effective as a disinfectant than 70% ethanol?

Accepted Answer

100% ethanol evaporates too quickly and does not penetrate cells as effectively 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 equations represents the action of superoxide dismutase (SOD) in detoxifying reactive oxygen species?

Accepted Answer

$$O_2$$^- + $$O_2^- + 2H$$^+ \rightarrow H_2O_2 + $$O_2$$

Question 6

Which type of microorganism would be LEAST affected by pickling (high salt and acidic conditions)?

Accepted Answer

Extreme halophiles

Question 7

Which of the following statements about the Kirby-Bauer disk diffusion test is TRUE?

Accepted Answer

It measures the sensitivity of bacteria to various antimicrobial agents by the size of the zone of inhibition.

Question 8

Which of the following mechanisms is NOT a common way bacteria develop resistance to antibiotics?

Accepted Answer

Increasing the permeability of the cell wall to allow more drug entry

Question 9

Which of the following best describes the principle of selective toxicity?

Accepted Answer

A drug should harm the infectious agent without harming the host.

Question 10

Which of the following antimicrobial agents acts by inhibiting cell wall synthesis?

Accepted Answer

Penicillin

Question 11

A patient is infected with a Gram-negative bacterium. Which of the following antibiotics would be most effective based on its mechanism of action?

Accepted Answer

Aminoglycosides, which irreversibly attach to the 30S ribosomal subunit

Question 12

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

Accepted Answer

Humans obtain folic acid from their diet, while bacteria must synthesize it.

Question 13

Which of the following is a limitation of using an autoclave for sterilization?

Accepted Answer

Oily substances are not effectively sterilized.

Question 14

Which of the following best describes the action of UV light on microbial DNA?

Accepted Answer

It causes adjacent thymidine bases to dimerize, disrupting DNA replication.

Question 15

A bacterium that grows only at the bottom of a test tube of thioglycollate broth is most likely a(n):

Accepted Answer

Obligate anaerobe

Question 16

Which of the following is the correct equation for the catalase reaction?

Accepted Answer

$$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 17

Which of the following is a reason why hand sanitizers must contain more than 60% alcohol to be effective?

Accepted Answer

Lower concentrations do not denature proteins and dissolve lipids efficiently.

Question 18

Which of the following best explains why heavy metals such as silver are effective antimicrobial agents?

Accepted Answer

They react with proteins, disrupting microbial metabolism.

Question 19

Which of the following is a correct statement about the use of filtration for sterilization?

Accepted Answer

It is used for heat-sensitive liquids and can remove particles larger than 0.3 microns.

Limits to Microbial Growth and Methods of Microbial Control

Study Guide - Practice Questions