Chapter 7: The Control of Microbial Growth

Which of the following is a factor contributing to hospital-acquired infections?

1)Some bacteria can metabolized disinfectants 2)Gram-negative bacteria are often resistant to disinfectants, 3) Invasive procedures can provide a portal of entry for bacteria, 4)Bacteria may be present in commercial products such as mouthwash.

Which concentration of ethanol is the most effective bactericide?

70%

Which of the following substances is used for surgical hand scrubs?

Chlorhexidine

A disk-diffusion test using Staphylococcus gave the following results:which compound was the most effective against E. coli?

E) Can't tell

table 7.1 A disk-diffusion test using Staphylococcus gave the following results: Disinfectant Zone of inhibition (mm): A 0 B 2.5 C 10 D 5 In Table 7.1, which compound was bactericidal?

E) Can't tell

Assume that one culture is a freshly opened package of dried yeast with 0.1% moisture, another culture is the same yeast with 7.5% moisture, and the third culture is a package of yeast mixed with water. Each culture was exposed to 130°C in a hot-air oven. Which graph in Figure 7.1 most likely shows the yeast with 0.1% moisture?

C

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

Mycobacteria

If you were preparing nutrient agar at home and didn't have an autoclave, what could you use to sterilize the nutrient agar?

Pressure cooker at 121°C for 15 minutes

table 7.1 A disk-diffusion test using Staphylococcus gave the following results: Disinfectant Zone of inhibition (mm): A 0 B 2.5 C 10 D 5 In Table 7.1, which compound was the most effective against Staphylococcus?

table 7.1= C

foods are preserved with all of the following substances except?

biguanides

Which of the following does NOT directly result from application of heat?

cell lysis

A disk-diffusion test using Staphylococcus gave the following resultswhich compound was the most effective against?

desinfectant=C, zone of inhibition= 10 D

Place the following surfactants in order from the most effective to the least effective antimicrobial activity: 1-Soap; 2-Acid detergent; 3. cationic detergent

3, 2,1

In figure 7.2, the decimal reduction time (D value) for the culture is approximately

15 min.

In Figure 7.2, the thermal death time for this culture is

60 min.

what is the thermal death time for culture (a)

60 min.

Which one of the following does NOT belong with the others?

Acid-anionic detergents

Which of the following substances is NOT effective against nonenveloped viruses?

Alcohol

Figure 7.3 Assume 109 E. coli cells/ml are in a flask. Which graph in Figure 7.3 best depicts the effect of placing the culture in an autoclave for 15 min. at time x?

B

Table 7.2 The fate of E. coli O157:H7 in apple cider held at 8°C for 2 weeks, with and without preservatives, is shown below: Bacteria/ml Cider only 2.2 Cider with potassium sorbate 2.0 Sodium benzoate 0 Sorbate + benzoate 0 In Table 7.2, which preservative is most effective?

Benzoate

Which of these disinfectants acts by denaturing proteins?

Bisphenol

Which of the following will NOT destroy prions?

Boiling

A suspension of 106 Bacillus cereus endospores was put in a hot-air oven at 170°C. Plate counts were used to determine the number of endospores surviving at the time intervals shown. In Figure 7.2, the thermal death point for this culture is

Can't tell from the data provided.

Which of the following is a limitation of the autoclave?

D) Cannot be used with heat-labile materials

7) Iodophors differ from iodine (I2) in that iodophors

Don't stain, Are less irritating, Are longer lasting. Are combined with a nonionic detergent.

Table 7.3 The following data were obtained by incubating gram-positive bacteria in nutrient medium + disinfectant for 24 hr, then transferring one loopful to nutrient medium (subculturing). (+ = growth; - = no growth) Doom K.O. Dilution Initial Subculture Initial Subculture 1:16 - + + + 1:32 - + + + 1:64 - + + + 1:128 + + + + Mortum Sterl Dilution Initial Subculture Initia Subculture 1:16 - - - + 1:32 - + + + 1:64 + + + + 1:128 + + + + In Table 7.3, which disinfectant is the most effective at stopping bacterial growth?

Doom

Which of the following will NOT inactivate endospores?

High pressure

Which of the following substances can sterilize?

Ethylene oxide

which of the following substances is NOT an oxidizing agent?

Glutaraldehyde

Which of the following is NOT used to disinfect water?

Heat

Which one of the following does NOT belong with the others?

Hydrogen peroxide

Which of the following is the best method to sterilize heat-labile solutions?

Membrane filtration

Table 7.3 The following data were obtained by incubating gram-positive bacteria in nutrient medium + disinfectant for 24 hr, then transferring one loopful to nutrient medium (subculturing). (+ = growth; - = no growth) Doom K.O. Dilution Initial Subculture Initial Subculture 1:16 - + + + 1:32 - + + + 1:64 - + + + 1:128 + + + + Mortum Sterl Dilution Initial Subculture Initia Subculture 1:16 - - - + 1:32 - + + + 1:64 + + + + 1:128 + + + + In Table 7.3, which disinfectant was bactericidal?

Mortum

Which of the following affects the elimination of bacteria from an object?

Number of bacteria present, Temperature, pH, Presence of organic matter

Which of the following does NOT achieve sterilization?

Pasteurization

Glutaraldehyde is considered one of the most effective disinfectants for hospital use. Which of the following statements about glutaraldehyde is false?

Stains and corrodes

Bone and tendons for transplant are decontaminated by

Supercritical fluids.

Which of the following best describes the pattern of microbial death?

The cells in a population die at a constant rate

The antimicrobial activity of chlorine is due to which of the following?

The formation of hypochlorous acid

all of the fallowing statements concerning radiation as a method of microbial control are true EXEPT?

X rays are the most practical form of ionizing radiation for microbial control

Which graph in Figure 7.3 best depicts the effect of placing the culture at 7°C at time x?

d

Table 7.3 The following data were obtained by incubating gram-positive bacteria in nutrient medium + disinfectant for 24 hr, then transferring one loopful to nutrient medium (subculturing). (+ = growth; - = no growth) Doom K.O. Dilution Initial Subculture Initial Subculture 1:16 - + + + 1:32 - + + + 1:64 - + + + 1:128 + + + + Mortum Sterl Dilution Initial Subculture Initia Subculture 1:16 - - - + 1:32 - + + + 1:64 + + + + 1:128 + + + + In Table 7.3, which disinfectant was most effective against Salmonella?

e) Can't tell

Which one of the following pairs is mismatched?

e)Ultraviolet radiation - desiccation

Which of the following pairs is not correctly match?

merthiolate- open wounds

Which of the following will is NOT preserve foods?

microwaves