Chapter 7 - The Control Of Microbial Growth

1) 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

2) 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.

3) Which of the following chemical agents is used for sterilization? A) alcohol B) phenolics C) ethylene oxide D) chlorine E) soap

4) Which of the following substances is used for surgical hand scrubs? A) phenol B) chlorine bleach C) chlorhexidine D) soap E) glutaraldehyde

5) Which of the following pairs of terms is mismatched? A) bacteriostatic — kills vegetative bacterial cells B) germicide - kills microbes C) virucide - inactivates viruses D) sterilant — destroys all living microorganisms E) fungicide — kills yeasts and molds

6) 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 a hypochlorite ion E) disruption of the plasma membrane

7) Which of the following regarding antimicrobial control agents is FALSE? A) Contaminating organic debris such as blood or sputum decrease effectiveness. B) Some agents kill by denaturing microbial cell proteins. C) Some agents affect microbial cell membranes by dissolving lipids. D) Silver is used for treating antibiotic-resistant bacteria. E) Some agents inactivate viruses by attacking cell membrane lipids.

8) Which of the following does NOT achieve sterilization? A) dry heat B) pasteurization C) autoclave D) supercritical fluids E) ethylene oxide

9) Which of the following is a limitation of the autoclave? A) It requires an excessively long time to achieve sterilization. B) It cannot inactivate viruses. C) It cannot kill endospores. D) It cannot be used with heat-labile materials. E) It cannot be used with glassware.

10) An agent used to reduce the number of bacteria on a toilet would most accurately be called a(n) A) disinfectant. B) antiseptic. C) aseptic. D) fungicide. E) virucide.

11) Application of heat to living cells can result in all of the following EXCEPT A) breaking of hydrogen bonds. B) alteration of membrane permeability. C) denaturation of enzymes. D) decreased thermal death time. E) damage to nucleic acids.

12) Which of the following disinfectants acts by disrupting the plasma membrane? A) soaps B) aldehydes C) bisphenols D) halogens E) heavy metals

13) Oxidizing agents include all of the following EXCEPT A) chlorine. B) glutaraldehyde. C) hydrogen peroxide. D) iodine. E) ozone.

14) Disinfection of water is achieved by all of the following EXCEPT A) ozone. B) UV radiation. C) chlorine. D) copper sulfate. E) peracetic acid.

15) All of the following substances are effective against nonenveloped viruses EXCEPT A) alcohol. B) chlorine. C) ethylene oxide. D) ozone. E) None of the answers is correct; all of these are equally effective against nonenveloped viruses.

16) Which of the following methods is used to preserve food by slowing the metabolic processes of foodborne microbes? A) lyophilization B) nonionizing radiation C) freezing D) ionizing radiation E) pasteurization

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

18) All of the following factors contribute to hospital-acquired infections EXCEPT 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) None of the answers is correct; all of these factors may contribute to hospital-acquired infection.

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

20) 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

21) Which of the following regarding antimicrobial control agents is FALSE? A) Contaminating organic debris such as blood or sputum will decrease effectiveness. B) Some agents kill by denaturing microbial cell proteins. C) Some agents affect microbial cell membranes by dissolving lipids. D) Some agents are utilized as both an antiseptic and a disinfectant. E) A true antimicrobial control agent is equally effective against both bacteria and viruses.

Figure 7.1 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. 22) In Figure 7.1, what is the thermal death time? A) 150°C B) 60 minutes C) 120 minutes D) 100°C E) The answer cannot be determined based on the information provided.

23) In Figure 7.1, the thermal death point for this culture is A) 15 minutes. B) 50°C. C) 30 minutes. D) 170°C. E) The answer cannot be determined based on the information provided

24) In Figure 7.1, the decimal reduction time (D value) for the culture is approximately A) 0 minutes. B) 10 minutes. C) 30 minutes. D) 40 minutes. E) 60 minutes.

25) Which of the following results in lethal damage to nucleic acids? A) heat B) radiation C) certain chemicals D) heat and radiation E) heat, radiation, and some chemicals

26) Which of the following pairs is mismatched? A) Ag — wound dressings B) alcohols — open wounds C) CuSO4 — algicide D) H2O2 — open wounds E) organic acids — food preservation

Figure 7.2 Assume 109 E. coli cells/ml are in a flask. 27) Which graph in Figure 7.2 best depicts the effect of placing the culture in an autoclave for 15 minutes at time x? A) a B) b C) c D) d E) e

28) Which graph in Figure 7.2 best depicts the effect of placing the culture at 7°C at time x? A) a B) b C) c D) d E) 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 29) In Table 7.1, which compound was the most effective against Staphylococcus? A) A B) B C) C D) D E) The answer cannot be determined based on the information provided.

30) In Table 7.1, which compound was the most effective against E. coli? A) A B) B C) C D) D E) The answer cannot be determined based on the information provided.

31) In Table 7.1, which compound was bactericidal? A) A B) B C) C D) D E) The answer cannot be determined based on the information provided.

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 Potassium sorbate + sodium benzoate 0 32) In Table 7.2, which preservative is most effective? A) potassium sorbate B) sodium benzoate C) potassium sorbate + sodium benzoate D) no preservative

33) An iodophor is a(n) A) phenol. B) agent that reduces oxygen. C) quaternary ammonium compound. D) form of formaldehyde. E) iodine mixed with a surfactant.

34) Ethylene oxide A) is a good antiseptic. B) is not sporicidal. C) requires high heat to be effective. D) is a sterilizing agent. E) is the active chemical in household bleach.

35) All of the following substances are used to preserve foods EXCEPT A) biguanides. B) nisin. C) potassium sorbate. D) sodium nitrite. E) calcium propionate.

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) 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) The answer cannot be determined based on the information provided.

37) In Table 7.3, which disinfectant was bactericidal? A) Doom B) K.O. C) Mortum D) Sterl E) The answer cannot be determined based on the information provided.

38) In Table 7.3, which disinfectant was most effective against Salmonella? A) Doom B) K.O. C) Mortum D) Sterl E) The answer cannot be determined based on the information provided.

39) All of the following are effective for destroying prions EXCEPT A) boiling. B) incineration. C) NaOH + autoclaving at 134°C. D) proteases. E) None of the answers are correct; each of these will destroy prions.

40) Which 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

41) All of the following are methods of food preservation EXCEPT A) desiccation. B) high pressure. C) ionizing radiation. D) microwaves. E) osmotic pressure.

42) The preservation of beef jerky from microbial growth relies on which method of microbial control? A) filtration B) lyophilization C) desiccation D) ionizing radiation E) supercritical CO2

43) If you were preparing nutrient agar at home and did not have an autoclave, what could you use to sterilize the nutrient agar? A) bleach B) boiling for one hour C) hydrogen peroxide D) oven at 121°C for one hour E) pressure cooker at 121°C for 15 minutes

44) Bone and tendons for transplant are decontaminated by A) ethylene oxide. B) glutaraldehyde. C) peroxygens. D) plasma sterilization. E) supercritical fluids.

45) 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

1) Any process that destroys the non-spore forming contaminants on inanimate objects is sterilization.

2) Desiccation is a reliable form of sterilization.

3) The thermal death time is the time needed to kill all the bacteria in a particular culture at a certain temperature.

4) Pseudomonas has been found growing in quaternary ammonium compounds (quats).

5) Moist heat destroys organisms by denaturing proteins.

6) Some antimicrobial chemicals are considered to be disinfectants and antiseptics.

7) The pH of the medium has no effect on the activity of the disinfectant being applied.

8) Ultraviolet light (UV) causes irreversible breaks in DNA strands.

9) Autoclaving is the most effective method of moist heat sterilization.

10) Microorganisms placed in high concentrations of salts and sugars undergo lysis.