Question 1

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

Accepted Answer

Sterilization removes all microorganisms, including endospores and viruses, while disinfection eliminates most pathogens but may leave some viable microbes.

Question 2

A hospital needs to sterilize heat-sensitive plastic instruments. Which method is most appropriate?

Accepted Answer

Ethylene oxide gas sterilization

Question 3

Which of the following organisms is LEAST susceptible to chemical disinfectants?

Accepted Answer

Bacterial endospores

Question 4

A food production facility wants to reduce microbial contamination without altering the taste or texture of the food. Which method is most suitable?

Accepted Answer

Pasteurization

Question 5

Which of the following statements about decimal reduction time ($$D$$ value) is correct?

Accepted Answer

It is the time required to kill 90% of a microbial population under specific conditions.

Question 6

Which chemical class is most effective for disinfecting food preparation surfaces due to its low toxicity and ability to reduce surface tension?

Accepted Answer

Quaternary ammonium compounds (Quats)

Question 7

Why is hydrogen peroxide more effective as a disinfectant on inanimate objects than on living tissue?

Accepted Answer

Living tissue produces catalase, which breaks down hydrogen peroxide into water and oxygen.

Question 8

Which of the following is a limitation of ultraviolet (UV) radiation for microbial control?

Accepted Answer

It has poor penetrating power and is less effective on covered or shaded surfaces.

Question 9

A laboratory is disposing of contaminated petri dishes by burning them in a high-temperature furnace. Which method of microbial control is being used?

Accepted Answer

Incineration (a form of dry heat sterilization)

Question 10

Which of the following statements about the use of chlorine in water treatment is correct?

Accepted Answer

Chlorine can react with naturally occurring chemicals to form disinfection by-products (DBPs), some of which are linked to long-term health risks.

Question 11

Which of the following is a reason why heat is not always suitable for sterilizing all items?

Accepted Answer

Some items, such as plastics, are heat-sensitive and may be damaged.

Question 12

Which of the following best explains why Staphylococcus aureus can survive in high salt environments?

Accepted Answer

It is able to tolerate plasmolysis caused by increased environmental solutes.

Question 13

Which of the following chemical agents is most likely to be used for sterilizing heat- and moisture-sensitive medical equipment, but is also a potential carcinogen?

Accepted Answer

Ethylene oxide

Question 14

A microbiology laboratory uses a HEPA filter to remove microbes from the air. What is the pore size of a typical HEPA filter?

Accepted Answer

$$0.3\ \mu m$$

Question 15

Which of the following is a major limitation of using alcohols as disinfectants?

Accepted Answer

They evaporate quickly, limiting contact time.

Question 16

Which of the following is the primary mode of action for phenolic compounds?

Accepted Answer

Disrupting plasma membranes and denaturing proteins

Question 17

A solution is heated to $$72^{\circ}C$ and held for 15 seconds to reduce microbial load. Which process is being described?

Accepted Answer

High-temperature short-time (HTST) pasteurization

Question 18

Which of the following is a key advantage of peroxygens such as hydrogen peroxide and peracetic acid?

Accepted Answer

They are powerful oxidizing agents and readily biodegradable.

Question 19

Which of the following best describes the effect of environmental conditions on the effectiveness of chemical disinfectants?

Accepted Answer

Higher temperatures and lower pH generally increase effectiveness, while organic matter can decrease effectiveness.

Question 20

Which preservation method works by causing cellular plasmolysis through increased environmental solutes?

Accepted Answer

Salting

Control of Microbial Growth: Physical and Chemical Methods

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