Question 1

A hospital is sterilizing surgical instruments using an autoclave. Which of the following best explains why autoclaving is more effective than boiling water for sterilization?

Accepted Answer

Autoclaving uses higher pressure to increase the boiling point of water, allowing temperatures above 100°C to be reached, which kills endospores.

Question 2

A food company wants to sterilize a heat-sensitive vitamin solution. Which method would be most appropriate?

Accepted Answer

Filtration through a membrane with $$0.22\ \mu m$$ pores

Question 3

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

Accepted Answer

Microbial death is exponential, with a constant proportion of the population dying per unit time.

Question 4

A researcher is using the disk-diffusion method to test disinfectants. What does a large clear zone around a disk indicate?

Accepted Answer

The disinfectant is more effective at inhibiting bacterial growth.

Question 5

Which of the following is the correct equation for the formation of hypochlorous acid when chlorine is added to water?

Accepted Answer

$$Cl_2 + H_2O$$ \rightarrow H^+ + Cl^- + HOCl$$

Question 6

Which of the following best describes the mechanism by which ionizing radiation kills microorganisms?

Accepted Answer

It dislodges electrons from atoms, forming free radicals that damage DNA.

Question 7

A patient with a deep wound is treated with hydrogen peroxide. Why might this treatment be less effective than expected?

Accepted Answer

Hydrogen peroxide is quickly broken down by catalase in human cells.

Question 8

Which of the following is a major disadvantage of using ethylene oxide as a sterilizing agent?

Accepted Answer

It is highly explosive and potentially carcinogenic.

Question 9

Which of the following is the most resistant to chemical biocides?

Accepted Answer

Prions

Question 10

A laboratory is using a HEPA filter to sterilize air in a burn unit. What is the minimum particle size that a HEPA filter can effectively remove?

Accepted Answer

$$0.3\ \mu m$$

Question 11

Which of the following best explains why quaternary ammonium compounds (quats) are not effective against endospores?

Accepted Answer

Endospores lack the cell membrane targets that quats disrupt.

Question 12

A food manufacturer uses sodium nitrite to preserve meat. What is a potential health risk associated with this practice?

Accepted Answer

Sodium nitrite can react with amino acids to form nitrosamines, which are carcinogenic.

Question 13

Which of the following is the most effective wavelength of ultraviolet (UV) light for killing microorganisms?

Accepted Answer

$$260\ nm$$

Question 14

Which of the following best describes the action of organic acids as food preservatives?

Accepted Answer

They inhibit microbial metabolism in acidic conditions (pH \u003c 3.6).

Question 15

A microbiologist is testing the effectiveness of a new disinfectant using the use-dilution test. Which of the following best describes this method?

Accepted Answer

Measuring the ability of the disinfectant to prevent growth on beads dipped in bacterial culture.

Question 16

Which of the following is a reason why moist heat is generally more effective than dry heat for sterilization?

Accepted Answer

Moist heat denatures proteins more rapidly due to better heat transfer.

Question 17

Which of the following best explains why refrigeration is considered bacteriostatic rather than bactericidal?

Accepted Answer

Refrigeration slows the metabolic rate of microbes, preventing reproduction and toxin production.

Question 18

A laboratory is using direct flaming to sterilize inoculating loops. What is the primary mechanism by which this method kills microorganisms?

Accepted Answer

Oxidation of cellular components

Question 19

Which of the following statements about the effectiveness of chemical antimicrobials is correct?

Accepted Answer

Endospores, cysts, and mycobacteria are relatively resistant to chemical agents.

Question 20

A hospital is considering using peracetic acid to sterilize medical instruments. Which of the following is a major advantage of peracetic acid?

Accepted Answer

It leaves no toxic residues and is effective against endospores and viruses.

Control of Microbial Growth: Methods and Principles

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