Question 1

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

Accepted Answer

Sterilization removes all microbial life including endospores, while disinfection removes only pathogens from non-living surfaces.

Question 2

A hospital is preparing surgical instruments for use. Which method would be most effective for ensuring all microbial life, including endospores, is eliminated?

Accepted Answer

Autoclaving at $$121\, ^\circ\mathrm{C}$$ for 15 minutes under 15 psi pressure

Question 3

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

Accepted Answer

When plotted logarithmically, the death curve is a straight line, indicating a constant rate of microbial death.

Question 4

A laboratory technician needs to sterilize a heat-sensitive enzyme solution. Which method is most appropriate?

Accepted Answer

Filtration using a $$0.22\, \mu\mathrm{m}$$ membrane filter

Question 5

Which of the following is the main mechanism by which moist heat kills microorganisms?

Accepted Answer

Denaturation of enzymes

Question 6

A food processing plant uses high concentrations of salt to preserve meat. What is the primary effect of this method on microbial cells?

Accepted Answer

It causes plasmolysis by creating a hypertonic environment, leading to water loss from cells.

Question 7

Which of the following statements about the effectiveness of chemical disinfectants is TRUE?

Accepted Answer

Gram-positive bacteria are generally more susceptible to disinfectants than gram-negative bacteria.

Question 8

Which of the following is a correct equivalent treatment for pasteurization?

Accepted Answer

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

Question 9

A researcher is using UV radiation to disinfect a laboratory surface. Which of the following statements is correct regarding UV radiation?

Accepted Answer

It causes thymine dimers in DNA, interfering with replication.

Question 10

Which of the following disinfectants acts by inactivating proteins through covalent cross-linking with functional groups such as $$-\mathrm{NH}_2$$, $$-\mathrm{OH}$$, $$-\mathrm{COOH}$$, and $$-\mathrm{SH}$$?

Accepted Answer

Aldehydes (e.g., formaldehyde, glutaraldehyde)

Question 11

Which of the following best explains why Pseudomonas species are difficult to control with quaternary ammonium compounds (quats)?

Accepted Answer

They can actively grow in quats, showing resistance to these disinfectants.

Question 12

A solution contains $$1,000,000$$ bacteria. If the decimal reduction time (DRT) is $$1$$ minute, how many bacteria will remain after $$3$$ minutes of treatment?

Accepted Answer

$$1,000$$

Question 13

Which of the following is a property of phenolics that makes them effective against Mycobacteria?

Accepted Answer

They disrupt plasma membranes, which is effective due to the high lipid content in Mycobacteria cell walls.

Question 14

Which of the following is NOT a principle of effective disinfection?

Accepted Answer

The color of the disinfectant

Question 15

Which of the following statements about desiccation is correct?

Accepted Answer

Viruses and endospores can resist desiccation, but endospores are more resistant than viruses.

Question 16

Which of the following is a reason why organic acids such as sorbic acid and benzoic acid are used as food preservatives?

Accepted Answer

They inhibit microbial metabolism, controlling molds and bacteria in foods.

Question 17

A nurse swabs a patient's skin with alcohol before an injection. This is an example of which microbial control method?

Accepted Answer

Degerming

Question 18

Which of the following statements about the use of refrigeration for microbial control is correct?

Accepted Answer

Most pathogenic microorganisms do not reproduce at $$0-7\, ^\circ\mathrm{C}$$, except Listeria.

Question 19

Which of the following is the most effective germicidal wavelength for ultraviolet (UV) radiation?

Accepted Answer

$$260\, \mathrm{nm}$$

Question 20

Which of the following best describes the action of heavy metals such as silver and mercury as antimicrobial agents?

Accepted Answer

They denature proteins by combining with sulfhydryl ($$-\mathrm{SH}) $$groups.

Chapter 7: The Control of Microbial Growth – Study Notes

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