Chapter 7- The Control of Microbial Growth

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Answer: C

Which of the following is the best method to sterilize heat-labile solutions? A) Dry heat B) Autoclave C) Membrane filtration D) Pasteurization E) Freezing

Answer: A

Which of the following best describes the pattern of microbial death? A) The cells in a population die at a constant rate. B) All the cells in a culture die at once. C) Not all of the cells in a culture are killed. D) The pattern varies depending on the antimicrobial agent. E) The pattern varies depending on the species.

Answer: C

Which of the following substances can sterilize? A) Alcohol B) Phenolics C) Ethylene oxide D) Chlorine E) Soap

Answer: C

Which of the following substances is used for surgical hand scrubs? A) Phenol B) Chlorine bleach C) Chlorhexidine D) Soap E) Glutaraldehyde

Answer: D

Place the following surfactants in order from the most effective to the least effective antimicrobial activity: 1-Soap; 2-Acid-anionic detergent; 3-Quats. A) 1, 2, 3 B) 1, 3, 2 C) 2, 1, 3 D) 3, 2, 1 E) 3, 1, 2

Answer: A

The antimicrobial activity of chlorine is due to which of the following? A) The formation of hypochlorous acid B) The formation of hydrochloric acid C) The formation of ozone D) The formation of free O E) Disruption of the plasma membrane

Answer: E

7) Iodophors differ from iodine (I2) in that iodophors A) Don’t stain. B) Are less irritating. C) Are longer lasting. D) Are combined with a nonionic detergent. E) All of the above.

Answer: B

Which of the following does NOT achieve sterilization? A) Dry heat B) Pasteurization C) Autoclave D) Formaldehyde E) Ethylene oxide

Answer: D

Which of the following is a limitation of the autoclave? A) Requires a long time to achieve sterilization B) Cannot inactivate viruses C) Cannot kill endospores D) Cannot be used with heat-labile materials E) Cannot be used with glassware

Answer: E

Which of the following affects the elimination of bacteria from an object? A) Number of bacteria present B) Temperature C) pH D) Presence of organic matter E) All of the above

Answer: D

Which of the following does NOT directly result from application of heat? A) Breaking of hydrogen bonds B) Breaking of sulfhydryl bonds C) Denaturing of enzymes D) Cell lysis E) Damage to nucleic acids

Answer: C

Which of these disinfectants acts by denaturing proteins? A) Alcohols B) Aldehydes C) Bisphenols D) Halogens E) Phenolics

Answer: B

Which of the following substances is NOT an oxidizing agent? A) Chlorine B) Glutaraldehyde C) Hydrogen peroxide D) Iodine E) Ozone

Answer: E

Which of the following is NOT used to disinfect water? A) Ozone B) Gamma radiation C) Chlorine D) Copper sulfate E) Heat

Answer: A

Which of the following substances is NOT effective against nonenveloped viruses? A) Alcohol B) Chlorine C) Ethylene oxide D) Ozone E) All are equally effective.

Answer: A

Glutaraldehyde is considered one of the most effective disinfectants for hospital use. Which of the following statements about glutaraldehyde is false? A) Stains and corrodes B) Is safe to transport C) Acts rapidly D) Is not hampered by organic material E) Attacks all microorganisms

Answer: B

Which concentration of ethanol is the most effective bactericide? A) 100% B) 70% C) 50% D) 40% E) 30%

Answer: E

Which of the following is NOT a factor contributing to hospital-acquired infections? A) Some bacteria metabolize disinfectants. B) Gram-negative bacteria are often resistant to disinfectants. C) Invasive procedures can provide a portal of entry for bacteria. D) Bacteria may be present in commercial products such as mouthwash. E) All of the above may contribute to hospital-acquired infection.

Answer: D

Which of the following treatments is the most effective for controlling microbial growth? A) 63°C for 30 min. B) 72°C for 15 sec. C) 140°C for 4 sec. D) They are equivalent treatments. E) None is effective.

Answer: B

Which of the following could be used to sterilize plastic Petri plates in a plastic wrapper? A) Autoclave B) Gamma radiation C) Microwaves D) Sunlight E) Ultraviolet radiation

Answer: B

In Figure 7.1, what is the thermal death time for culture (a)? A) 150°C B) 60 min. C) 120 min. D) 100°C E) Can’t tell

Answer: C

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? A) a B) b C) c D) a and b E) b and c

Answer: E

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. 23) In Figure 7.2, the thermal death point for this culture is A) 15 min. B) 50°C. C) 30 min. D) 170°C. E) Can’t tell from the data provided.

Answer: B

In Figure 7.2, the decimal reduction time (D value) for the culture is approximately A) 0 min. B) 15 min. C) 30 min. D) 45 min. E) 60 min.

Answer: E

In Figure 7.2, the thermal death time for this culture is A) 0 min. B) 10 min. C) 20 min. D) 40 min. E) 60 min.

Answer: B

Which of the following pairs is mismatched? A) Ag – burns B) Alcohols – open wounds C) CuSO4 – algicide D) H2O2 – open wounds E) Organic acids – food preservation

Answer: B

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? A) a B) b C) c D) d E) e

Answer: D

Which graph in Figure 7.3 best depicts the effect of placing the culture at 7°C at time x? A) a B) b C) c D) d E) e

Answer: C

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 29) In Table 7.1, which compound was the most effective against Staphylococcus? A) A B) B C) C D) D E) Can’t tell

Answer: E

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 E. coli? A) A B) B C) C D) D E) Can’t tell

Answer: E

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? A) A B) B C) C D) D E) Can’t tell

Answer: 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 32) In Table 7.2, which preservative is most effective? A) Sorbate B) Benzoate C) Sorbate + benzoate D) No preservative

Answer: A

Which one of the following does NOT belong with the others? A) Acid-anionic detergents B) Benzoic acid C) Supercritical CO2 D) Pasteurization E) Peracetic acid

Answer: D

Which one of the following does NOT belong with the others? A) Beta-propiolactone B) Glutaraldehyde C) Ethylene oxide D) Hydrogen peroxide E) Propylene oxide

Answer: A

Which of the following substances is NOT used to preserve foods? A) Biguanides B) Nisin C) Potassium sorbate D) Sodium nitrite E) Sodium propionate

Answer: A

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 Initial Subculture 1:16 – – – + 1:32 – + + + 1:64 + + + + 1:128 + + + + 36) In Table 7.3, which disinfectant is the most effective at stopping bacterial growth? A) Doom B) K.O. C) Mortum D) Sterl E) Can’t tell

Answer: C

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 Initial Subculture 1:16 – – – + 1:32 – + + + 1:64 + + + + 1:128 + + + + In Table 7.3, which disinfectant was bactericidal? A) Doom B) K.O. C) Mortum D) Sterl E) Can’t tell

Answer: E

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 Initial Subculture 1:16 – – – + 1:32 – + + + 1:64 + + + + 1:128 + + + + In Table 7.3, which disinfectant was most effective against Salmonella? A) Doom B) K.O. C) Mortum D) Sterl E) Can’t tell

Answer: A

Which of the following will NOT destroy prions? A) Boiling B) Incineration C) NaOH + autoclaving at 134°C D) Proteases E) All of the above destroy prions.

Answer: E

Which one of the following pairs is mismatched? A) Ionizing radiation – hydroxyl radicals B) Ozone – takes electrons from substances C) Plasma sterilization – free radicals D) Supercritical fluids – CO2 E) Ultraviolet radiation – desiccation

Answer: D

Which of the following will NOT preserve foods? A) Desiccation B) High pressure C) Ionizing radiation D) Microwaves E) Osmotic pressure

Answer: C

Which of the following will NOT inactivate endospores? A) Autoclave B) Chlorine dioxide C) High pressure D) Plasma E) Supercritical CO2

Answer: E

If you were preparing nutrient agar at home and didn’t have an autoclave, what could you use to sterilize the nutrient agar? A) Bleach B) Boiling for 1 hour C) Hydrogen peroxide D) Oven at 121°C for 1 hour E) Pressure cooker at 121°C for 15 minutes

Answer: E

Bone and tendons for transplant are decontaminated by A) Ethylene oxide. B) Glutaraldehyde. C) Peroxygens. D) Plasma sterilization. E) Supercritical fluids.

Answer: C

Which one of the following is most resistant to chemical biocides? A) Gram-negative bacteria B) Gram-positive bacteria C) Mycobacteria D) Protozoan cysts E) Viruses with lipid envelopes

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