Question 1

Which of the following best defines sterilization in microbiology?

Accepted Answer

The destruction or removal of all forms of microbial life, including endospores.

Question 2

A hospital uses an autoclave to sterilize surgical instruments. What are the standard conditions for autoclaving to achieve sterilization?

Accepted Answer

$$121^\circ\mathrm{C} at 15 $$psi above atmospheric pressure for 15 minutes

Question 3

Which of the following statements about the microbial death curve is correct?

Accepted Answer

Microbial populations die at a constant rate when exposed to a sterilizing agent, resulting in a straight line when plotted logarithmically.

Question 4

Why are Gram-negative bacteria generally more resistant to chemical biocides than Gram-positive bacteria?

Accepted Answer

They possess an outer membrane that restricts entry of chemicals and can metabolize many chemicals.

Question 5

Which physical method is most appropriate for sterilizing heat-sensitive plastic labware?

Accepted Answer

Ionizing radiation

Question 6

A solution contains $$1 	imes 10^6$ bacteria. If the death rate is 90% per minute, how many bacteria remain after 2 minutes?

Accepted Answer

$$1 	imes 10^5$

Question 7

Which of the following is a major advantage of glutaraldehyde over other chemical disinfectants?

Accepted Answer

It can sterilize delicate surgical instruments, including those with endospores.

Question 8

Which of the following best explains why alcohol is effective against enveloped viruses but not nonenveloped viruses?

Accepted Answer

Alcohol dissolves lipid envelopes, inactivating enveloped viruses, but nonenveloped viruses lack this structure.

Question 9

A food processing plant wants to reduce the risk of botulism in canned foods. Which method is most effective?

Accepted Answer

Commercial sterilization to kill $$Clostridium~botulinum$$ endospores

Question 10

Which chemical disinfectant is most appropriate for use on living tissue?

Accepted Answer

Iodophor (e.g., Betadine)

Question 11

Which of the following statements about the disk-diffusion method is correct?

Accepted Answer

The method measures the effectiveness of a chemical agent against a specific microbe on an agar plate.

Question 12

Which of the following is NOT a reason why handwashing is considered the single most effective measure for microbial growth control?

Accepted Answer

It kills all endospores present on the skin.

Question 13

Which of the following statements about pasteurization is TRUE?

Accepted Answer

High-temperature short-time (HTST) pasteurization is typically $$72^\circ\mathrm{C}$$ for 15 seconds.

Question 14

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

Accepted Answer

Steam must directly contact the material to sterilize it.

Question 15

Which of the following best describes the action of quaternary ammonium compounds (quats)?

Accepted Answer

They are strongly bactericidal against Gram-positive bacteria by disrupting plasma membranes.

Question 16

Which of the following methods is most effective for sterilizing heat-sensitive solutions such as certain antibiotics or vaccines?

Accepted Answer

Filtration using membrane filters with pore sizes of $$0.2~\mu m$$

Question 17

Which of the following is a reason why naked viruses are more resistant to chemical control agents than enveloped viruses?

Accepted Answer

Their capsid is more resistant to drying, acid, and detergents.

Question 18

Which of the following statements about the use of hydrogen peroxide as a disinfectant is correct?

Accepted Answer

It is especially effective against anaerobic bacteria because they lack catalase.

Question 19

Which of the following is a risk associated with the use of sodium nitrite as a food preservative?

Accepted Answer

It can be converted to nitrosamines, which are carcinogenic.

Question 20

Which of the following best explains why the presence of organic matter can inhibit the effectiveness of a disinfectant?

Accepted Answer

Organic matter can react with and inactivate the disinfectant, reducing its availability to kill microbes.

Chapter 7: The Control of Microbial Growth – Study Notes

Study Guide - Practice Questions