Question 1

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

Accepted Answer

Sterilization removes all forms of microbial life, including endospores, while disinfection destroys only harmful vegetative microorganisms.

Question 2

A hospital technician needs to sterilize heat-sensitive plastic syringes. Which method is most appropriate and why?

Accepted Answer

Use a chemical sterilant, because high heat would damage the plastic.

Question 3

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

Accepted Answer

Microbial death occurs at a constant rate, meaning a fixed percentage of cells die per unit time.

Question 4

A solution contains $10^6$ bacteria. If the decimal reduction time (DRT) is 2 minutes, how many bacteria remain after 6 minutes of treatment?

Accepted Answer

$10^3$

Question 5

Which of the following is a key reason why phenolics are useful for disinfecting organic-rich materials such as pus or feces?

Accepted Answer

Phenolics remain active in the presence of organic compounds.

Question 6

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 efficiently by breaking hydrogen bonds.

Question 7

A bacteriostatic agent is applied to a bacterial culture. What is the expected outcome if the agent is later removed?

Accepted Answer

Bacterial growth may resume.

Question 8

Which of the following chemical agents is most appropriate for use as a surgical hand scrub due to its effectiveness against both gram-positive and gram-negative bacteria?

Accepted Answer

Chlorhexidine (a biguanide)

Question 9

A laboratory is testing the effectiveness of a new disinfectant using the disk-diffusion method. What result would indicate the disinfectant is effective?

Accepted Answer

A clear zone of inhibition appears around the disk.

Question 10

Which of the following statements about alcohols as disinfectants is correct?

Accepted Answer

Alcohols are not effective against endospores and nonenveloped viruses.

Question 11

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

Accepted Answer

It creates reactive hydroxyl radicals that damage DNA.

Question 12

A food processing plant wants to prevent the growth of Clostridium botulinum in canned meats. Which chemical preservative is most appropriate?

Accepted Answer

Nitrates

Question 13

Which of the following is a limitation of using autoclaving for sterilization?

Accepted Answer

It can damage heat-sensitive materials such as some plastics.

Question 14

A hospital is considering two disinfectants. Disinfectant A is highly effective at low concentrations but is inactivated by organic matter. Disinfectant B is less potent but remains active in the presence of organic matter. Which is preferable for cleaning blood spills and why?

Accepted Answer

Disinfectant B, because it remains active in the presence of organic matter.

Question 15

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

Accepted Answer

They disrupt plasma membranes and denature proteins.

Question 16

A microbiologist is using the decimal reduction time (DRT) to compare two disinfectants. Disinfectant X has a DRT of 1 minute, and Disinfectant Y has a DRT of 3 minutes. Which is more effective and why?

Accepted Answer

Disinfectant X, because it kills 90% of bacteria in less time.

Question 17

Which of the following is the correct definition of thermal death point (TDP)?

Accepted Answer

The lowest temperature at which all microbes in a liquid suspension are killed in 10 minutes.

Question 18

Which of the following is a real-world example of degerming?

Accepted Answer

Washing your hands with soap and water before surgery.

Question 19

Which of the following best describes the action of aldehydes as antimicrobial agents?

Accepted Answer

They inactivate proteins by cross-linking with functional groups such as $-\mathrm{NH}_2$, $-\mathrm{OH}$, $-\mathrm{COOH}$, and $-\mathrm{SH}$.

Question 20

A patient is treated with a bacteriostatic antibiotic. What is the most likely outcome if the patient's immune system is compromised?

Accepted Answer

The infection may persist or worsen because the bacteria are not killed, only inhibited.

Control of Microbial Growth: Principles and Methods

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