Q: A typical microbial death curve is plotted logarithmically. If a population of 10,000 bacteria is exposed to a disinfectant and the death rate is constant, how many bacteria remain after 3 minutes if the death rate is 90% per minute?

$$10,000 \times (0.1)^3$ = 10$$

Question 1

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

Accepted Answer

Sterilization destroys all forms of microbial life, including endospores; disinfection destroys only vegetative pathogens.

Question 2

A hospital autoclave operates at 121°C and 15 psi for 15 minutes. What is the primary mechanism by which this process kills microorganisms?

Accepted Answer

Denaturation of proteins by moist heat

Question 3

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

Accepted Answer

Filtration

Question 4

A typical microbial death curve is plotted logarithmically. If a population of 10,000 bacteria is exposed to a disinfectant and the death rate is constant, how many bacteria remain after 3 minutes if the death rate is 90% per minute?

Accepted Answer

$$10,000 	imes (0.1)^3$ = 10$$

Question 5

Which of the following chemical agents disrupts plasma membranes and is commonly used in hand soaps and detergents?

Accepted Answer

Quaternary ammonium compounds

Question 6

Why are endospores more resistant to chemical and physical methods of microbial control than vegetative cells?

Accepted Answer

Endospores contain dipicolinic acid and a thick spore coat that protect their DNA.

Question 7

Which of the following statements about pasteurization is correct?

Accepted Answer

Pasteurization reduces microbial numbers and eliminates pathogens, but does not sterilize.

Question 8

A disinfectant is tested using the use-dilution method. Which result indicates the most effective disinfectant?

Accepted Answer

The disinfectant that prevents growth in all tubes after exposure to contaminated metal rings.

Question 9

Which of the following is a limitation of UV radiation as a method of microbial control?

Accepted Answer

It cannot penetrate surfaces or opaque objects.

Question 10

Which chemical agent is most effective for sterilizing medical equipment and is classified as a gaseous sterilant?

Accepted Answer

Ethylene oxide

Question 11

A solution contains 70% ethanol. What is the primary mechanism by which ethanol acts as a disinfectant?

Accepted Answer

Denaturation of proteins and disruption of membranes

Question 12

Which of the following best explains why high concentrations of salt or sugar preserve foods?

Accepted Answer

They create a hypertonic environment, causing plasmolysis in microbes.

Question 13

A nurse is cleaning a surface contaminated with Staphylococcus aureus. Which factor will most likely increase the effectiveness of the disinfectant used?

Accepted Answer

Increasing the concentration and contact time of the disinfectant

Question 14

Which of the following is the correct formula for calculating the decimal reduction time ($$D) in a $$microbial death curve?

Accepted Answer

$$D = \frac{	ext{Time}}{\log_{10}(N_0$) - \log_{10}(N)}$$

Question 15

Which of the following is a major disadvantage of using phenolics as disinfectants in a hospital setting?

Accepted Answer

They can cause skin irritation and have a strong odor.

Question 16

Which of the following statements about aldehydes is correct?

Accepted Answer

Aldehydes inactivate proteins by cross-linking functional groups.

Question 17

A food processing plant uses ionizing radiation to sterilize packaged foods. What is the main advantage of this method?

Accepted Answer

It leaves no residue and penetrates deeply into the food.

Question 18

Which of the following is the most resistant to chemical biocides?

Accepted Answer

Endospores

Question 19

A patient develops an infection after cosmetic surgery. The causative agent is found to be resistant to quaternary ammonium compounds. Which organism is most likely responsible?

Accepted Answer

Pseudomonas species

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