Question 1

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

Accepted Answer

Sterilization removes all microbial life, while disinfection only destroys harmful microorganisms on inanimate surfaces.

Question 2

A hospital is preparing surgical instruments for use. Which method would be most appropriate to ensure destruction of all organisms, including endospores, on these instruments?

Accepted Answer

Autoclaving at $$121^\circ\mathrm{C}$$ and 15 psi for 15 minutes

Question 3

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

Accepted Answer

They possess an outer membrane containing lipopolysaccharide that restricts entry of biocides.

Question 4

A solution contains $$1 	imes 10^6$ bacteria. If a sterilization process kills 90% of the bacteria every minute, how many bacteria remain after 3 minutes?

Accepted Answer

$$1 	imes 10^3$

Question 5

Which of the following statements about the use-dilution test is correct?

Accepted Answer

It measures the effectiveness of a disinfectant by exposing metal cylinders coated with bacteria to the disinfectant and then culturing them.

Question 6

Which physical method of microbial control is most appropriate for sterilizing heat-sensitive solutions such as vaccines?

Accepted Answer

Filtration through a membrane filter with pore size $$0.22\ \mu\mathrm{m}$$

Question 7

A food processing plant wants to reduce spoilage organisms and pathogens in milk without significantly affecting its taste. Which method should they use?

Accepted Answer

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

Question 8

Which of the following best explains why alcohol-based hand sanitizers are not effective against Clostridium difficile infections?

Accepted Answer

Alcohols do not destroy endospores, which are produced by Clostridium difficile.

Question 9

A laboratory technician needs to sterilize a large volume (9 liters) of nutrient broth. What is the main reason the autoclave cycle must be extended for this container compared to a 500 mL flask?

Accepted Answer

It takes longer for the center of a large volume to reach the sterilization temperature.

Question 10

Which chemical agent is most appropriate for sterilizing heat-sensitive medical equipment such as endoscopes?

Accepted Answer

Glutaraldehyde (liquid chemical sterilant)

Question 11

Which of the following statements about ionizing and nonionizing radiation is correct?

Accepted Answer

Ionizing radiation (such as gamma rays) penetrates deeply and causes lethal mutations by ionizing water to form hydroxyl radicals.

Question 12

A patient with a skin wound is treated with an antiseptic. Which of the following best defines an antiseptic?

Accepted Answer

A chemical that destroys harmful microorganisms on living tissue

Question 13

Which of the following is a limitation of using hydrogen peroxide as an antiseptic for open wounds?

Accepted Answer

It is rapidly broken down by catalase in tissues, reducing its effectiveness.

Question 14

Which of the following best describes the mechanism of action of phenolic compounds as disinfectants?

Accepted Answer

They disrupt plasma membranes, causing leakage of cellular contents.

Question 15

A food manufacturer wants to prevent the growth of Clostridium botulinum in packaged meats. Which preservative should be used?

Accepted Answer

Nitrites

Question 16

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

Accepted Answer

Moist heat coagulates and denatures proteins more efficiently than dry heat.

Question 17

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

Accepted Answer

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

Question 18

Which of the following statements about bacteriostasis is correct?

Accepted Answer

It refers to inhibiting the growth of microbes without killing them.

Question 19

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

Accepted Answer

$$0.3\ \mu\mathrm{m}$$

Question 20

Which of the following is a correct statement about the decimal reduction time (DRT) in microbial control?

Accepted Answer

It is the time required to kill 90% of a specific population of bacteria at a given temperature.

Microbial Control: Principles, Terminology, and Death Rates

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