Question 1

Which of the following statements best explains why Gram-negative bacteria are generally more resistant to chemical disinfectants than Gram-positive bacteria?

Accepted Answer

Gram-negative bacteria possess an external lipopolysaccharide (LPS) layer that acts as a barrier to many chemicals.

Question 2

A hospital is deciding between using phenolics and alcohols for disinfecting surfaces contaminated with Mycobacterium tuberculosis. Which chemical is more appropriate and why?

Accepted Answer

Phenolics, because they are lipid soluble and can damage the waxy mycobacterial cell wall.

Question 3

Which of the following factors does NOT significantly affect the efficacy of a chemical disinfectant?

Accepted Answer

The color of the disinfectant.

Question 4

A disk diffusion test is performed with chlorine, hexachlorophene, and o-phenylphenol on plates inoculated with Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Which chemical shows effectiveness against all three organisms?

Accepted Answer

Chlorine

Question 5

Which of the following best describes the mechanism of action of iodine as a disinfectant?

Accepted Answer

It impairs protein synthesis and alters cell membranes.

Question 6

Why is it important to pre-clean a surface before applying a chemical disinfectant?

Accepted Answer

Pre-cleaning removes organic material that can inactivate disinfectants.

Question 7

Which of the following is a major health and environmental concern associated with the widespread use of triclosan?

Accepted Answer

It can lead to the development of cross-resistance to antibiotics and disrupts environmental bacterial ecosystems.

Question 8

A use-dilution test is performed to evaluate a new disinfectant. Metal cylinders are dipped in cultures of Salmonella enterica, Staphylococcus aureus, and Pseudomonas aeruginosa, then exposed to the disinfectant. Which result would indicate the disinfectant is effective?

Accepted Answer

No growth is observed in the broth after cylinders are transferred.

Question 9

Which of the following statements about chlorine as a disinfectant is FALSE?

Accepted Answer

Chlorine is ineffective in the presence of organic matter.

Question 10

Which of the following best explains why Pseudomonas aeruginosa is particularly difficult to eliminate with chemical disinfectants?

Accepted Answer

It has an outer membrane that restricts entry of many biocides and can actively pump out toxic substances.

Question 11

Which of the following is a correct order of microbial resistance to chemical biocides, from most resistant to least resistant?

Accepted Answer

Prions \u003e Endospores \u003e Mycobacteria \u003e Gram-negative bacteria \u003e Gram-positive bacteria \u003e Viruses with lipid envelopes

Question 12

Which chemical agent is most appropriate for disinfecting skin prior to surgery, and why?

Accepted Answer

Chlorhexidine, because it causes gross permeability changes to cell membranes and is safe for use on skin.

Question 13

A solution of sodium hypochlorite is used to disinfect water. If 2-4 drops are added per liter and allowed to sit for 30 minutes, what is the primary chemical reaction responsible for disinfection?

Accepted Answer

$$Cl_2 + H_2O$$ \rightarrow HOCl + HCl$$

Question 14

Which of the following is a significant risk of using hexachlorophene-containing products, especially in infants?

Accepted Answer

It can be absorbed through the skin and cause neurological damage.

Question 15

Which of the following statements about bisphenols is TRUE?

Accepted Answer

Hexachlorophene is effective against Gram-positive staphylococci and streptococci.

Question 16

Which of the following best describes the main advantage of using iodophore formulations (such as Betadine) over tincture iodine for skin disinfection?

Accepted Answer

Iodophores do not stain and are less irritating to the skin.

Question 17

Which of the following is NOT a recommended use for chlorine-based disinfectants?

Accepted Answer

Sterilizing surgical instruments for invasive procedures.

Question 18

Which of the following best explains why surface-active agents (such as quaternary ammonium compounds) are less effective against Pseudomonas aeruginosa?

Accepted Answer

Pseudomonas aeruginosa produces enzymes that degrade these agents.

Chemical Control of Microbial Growth

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