Question 1

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

Accepted Answer

Sterilization destroys all forms of microbial life, including endospores, while disinfection eliminates most pathogens but not necessarily endospores.

Question 2

A hospital is evaluating a new disinfectant using the disk-diffusion method. Which result would indicate the disinfectant is effective?

Accepted Answer

A large zone of inhibition around the disk where bacteria do not grow.

Question 3

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

Accepted Answer

Prions

Question 4

Which equation represents the formation of hypochlorous acid when chlorine is added to water?

Accepted Answer

$$\mathrm{Cl_2$ + H_2O \rightarrow H^+ + Cl^- + HOCl}$$

Question 5

A laboratory technician needs to sterilize a heat-sensitive vitamin solution. Which method is most appropriate?

Accepted Answer

Membrane filtration

Question 6

Which of the following best explains why 70% ethanol is more effective as a disinfectant than 100% ethanol?

Accepted Answer

Water is required for protein denaturation, which is the main mechanism of action for ethanol.

Question 7

Which physical method of microbial control is most likely to cause thymine dimers in DNA?

Accepted Answer

Ultraviolet (UV) radiation

Question 8

A food processing plant wants to reduce microbial contamination in fruit juice without altering its flavor. Which method should they use?

Accepted Answer

Pasteurization

Question 9

Which of the following statements about phenolic compounds (such as those in Lysol) is correct?

Accepted Answer

They disrupt plasma membranes and denature proteins, and are effective even in the presence of organic matter.

Question 10

Which of the following is a disadvantage of using ionizing radiation for sterilization?

Accepted Answer

It may cause genetic mutations in humans due to its ability to penetrate tissues.

Question 11

A nurse is preparing a patient’s skin for surgery using Betadine. What is the active antimicrobial component in Betadine, and what is its mode of action?

Accepted Answer

Iodine; denatures proteins by breaking disulfide bonds

Question 12

Which of the following best describes the effect of high initial microbial load on the rate of killing by a disinfectant?

Accepted Answer

It takes longer to achieve sterilization because more microbes must be killed.

Question 13

Which chemical agent is commonly used to disinfect water, is a strong oxidizing agent, but is easily inactivated by organic material?

Accepted Answer

Chlorine

Question 14

Which of the following is a limitation of using UV light for disinfection?

Accepted Answer

It does not penetrate paper, glass, or cloth.

Question 15

Which of the following statements about aldehydes as chemical disinfectants is correct?

Accepted Answer

They inactivate proteins by forming covalent crosslinks with functional groups.

Question 16

A microbiologist is using a HEPA filter in a biosafety cabinet. What is the minimum particle size that the filter can remove from the air?

Accepted Answer

$$0.3\ \mu m$$

Question 17

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

Accepted Answer

It is rapidly broken down by catalase in human cells.

Question 18

Which of the following best describes the action of cationic detergents (quaternary ammonium compounds) as disinfectants?

Accepted Answer

They disrupt cell membranes by binding to negatively charged bacterial surface proteins.

Question 19

Which of the following is a unique advantage of glutaraldehyde over formaldehyde as a disinfectant?

Accepted Answer

It is less irritating and can act as a sterilizing agent.

Question 20

A patient develops an eye infection after swimming in a poorly maintained pool. Which chemical agent could have prevented this by killing algae and some bacteria in the water?

Accepted Answer

Copper sulfate

Physical and Chemical Controls of Microorganisms: Microbiology Study Guide

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