Q: A solution contains 1,000,000 bacteria. If the decimal reduction time (DRT) at 70°C is 2 minutes, how many bacteria will remain after 6 minutes?

$$1,000,000 \times (0.1)^3$ = 1,000$$

Question 1

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

Accepted Answer

Sterilization removes all living microorganisms, including endospores, while disinfection destroys only vegetative cells and some viruses.

Question 2

A hospital technician uses an autoclave to sterilize surgical instruments. If the autoclave operates at 121°C under 15 psi for 15 minutes, which microbial structure is most likely to survive if the process is incomplete?

Accepted Answer

Endospores

Question 3

Which of the following is the best definition of decimal reduction time (DRT)?

Accepted Answer

The time required to kill 90% of a microbial population at a given temperature.

Question 4

A disinfectant is tested using the disk-diffusion method. Which result indicates the highest effectiveness against a bacterial species?

Accepted Answer

A large zone of inhibition around the disk

Question 5

Which of the following chemical agents is most effective against biofilms and is commonly found in mouthwash?

Accepted Answer

Zinc chloride

Question 6

Which physical method of microbial control kills by oxidation and is used to sterilize inoculating loops in the laboratory?

Accepted Answer

Direct flaming

Question 7

Which of the following statements about alcohol-based hand sanitizers is correct?

Accepted Answer

They are not effective against endospore-forming bacteria such as Clostridium difficile.

Question 8

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

Accepted Answer

Moist heat denatures proteins more rapidly by breaking hydrogen bonds.

Question 9

A solution contains 1,000,000 bacteria. If the decimal reduction time (DRT) at 70°C is 2 minutes, how many bacteria will remain after 6 minutes?

Accepted Answer

$$1,000,000 	imes (0.1)^3$ = 1,000$$

Question 10

Which of the following is a limitation of using boiling as a method of sterilization?

Accepted Answer

Boiling does not reliably destroy endospores.

Question 11

Which of the following statements about phenolics is true?

Accepted Answer

They remain active in the presence of organic matter and are stable for long periods.

Question 12

Which of the following best describes the mechanism of action for ionizing radiation?

Accepted Answer

It ionizes water to create reactive hydroxyl radicals that damage DNA.

Question 13

A nurse wipes a patient’s skin with an alcohol swab before an injection. This is an example of:

Accepted Answer

Antisepsis

Question 14

Which of the following factors does NOT influence the effectiveness of an antimicrobial agent?

Accepted Answer

The color of the agent

Question 15

Which of the following best explains why quaternary ammonium compounds (quats) are effective disinfectants?

Accepted Answer

They are cationic, denature proteins, and disrupt plasma membranes.

Question 16

Which of the following is a real-world application of using aldehydes in microbial control?

Accepted Answer

Preserving biological specimens and inactivating bacteria in vaccines

Question 17

Which of the following is the main reason why test strips are used in autoclaving?

Accepted Answer

To indicate whether sterility has been achieved

Question 18

Which of the following best describes the effect of nonionizing radiation (UV light) on microbial DNA?

Accepted Answer

It creates thymine dimers, preventing correct DNA replication.

Question 19

Which of the following is a correct statement about the suffixes '-cide' and '-stat' in microbial control terminology?

Accepted Answer

'-cide' indicates killing of microbes, while '-stat' indicates inhibition of growth.

Question 20

Which of the following best explains why the rate of microbial death is plotted logarithmically?

Accepted Answer

Because a constant percentage of the population dies per unit time, resulting in a straight line on a logarithmic scale.

Control of Microbial Growth: Methods, Mechanisms, and Applications

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