Deck 7: The Control of Microbial Growth

Question 1

Which of the following methods is used to preserve food by slowing the metabolic processes of foodborne microbes?

A) ionizing radiation
B) nonionizing radiation
C) lyophilization
D) pasteurization
E) freezing

Answer 1

E

Question 2

Disinfection of water is achieved by all of the following EXCEPT

A) UV radiation.
B) chlorine.
C) peracetic acid.
D) copper sulfate.
E) ozone.

Answer 2

C

Question 3

Which of the following could be used to sterilize plastic Petri plates in a plastic wrapper?

A) ultraviolet radiation
B) microwaves
C) sunlight
D) gamma radiation
E) autoclave

Answer 3

D

Question 4

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

A) soap
B) chlorhexidine
C) chlorine bleach
D) glutaraldehyde
E) phenol

Question 5

Application of heat to living cells can result in all of the following EXCEPT

A) alteration of membrane permeability.
B) breaking of hydrogen bonds.
C) denaturation of enzymes.
D) damage to nucleic acids.
E) decreased thermal death time.

Question 6

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

Question 7

Which of the following is a limitation of the autoclave?

A) It cannot be used with glassware.
B) It requires an excessively long time to achieve sterilization.
C) It cannot kill endospores.
D) It cannot inactivate viruses.
E) It cannot be used with heat- labile materials.

Question 8

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.

In Figure 7.1, what is the thermal death time?

A) 120 minutes
B) 100°C
C) 60 minutes
D) 150°C
E) The answer cannot be determined based on the information provided.

Question 9

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

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

Question 10

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.

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.

Question 11

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

A) boiling for one hour
B) hydrogen peroxide
C) pressure cooker at 121°C for 15 minutes
D) oven at 121°C for one hour
E) bleach

Question 12

Figure 7.2
Assume 10⁹ E. coli cells/ml are in a flask.

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

Question 13

All of the following factors contribute to hospital- acquired infections EXCEPT

A) some bacteria metabolize disinfectants.
B) bacteria may be present in commercial products such as mouthwash.
C) invasive procedures can provide a portal of entry for bacteria.
D) gram- negative bacteria are often resistant to disinfectants.
E) None of the answers is correct; all of these factors may contribute to hospital- acquired infection.

Question 14

All of the following substances are used to preserve foods EXCEPT

A) potassium sorbate.
B) biguanides.
C) sodium nitrite.
D) calcium propionate.
E) nisin.

Question 15

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

A) gram- negative bacteria
B) viruses with lipid envelopes
C) protozoan cysts
D) mycobacteria
E) gram- positive bacteria

Question 16

The preservation of beef jerky from microbial growth relies on which method of microbial control?

A) ionizing radiation
B) filtration
C) lyophilization
D) desiccation
E) supercritical CO₂

Question 17

Which of the following disinfectants acts by disrupting the plasma membrane?

A) heavy metals
B) soaps
C) bisphenols
D) halogens
E) aldehydes

Question 18

Oxidizing agents include all of the following EXCEPT

A) ozone.
B) hydrogen peroxide.
C) chlorine.
D) glutaraldehyde.
E) iodine.

Question 19

Which of the following regarding antimicrobial control agents is FALSE?

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

Question 20

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.

Question 21

Which concentration of ethanol is the most effective bactericide?

A) 100 percent
B) 70 percent
C) 50 percent
D) 40 percent
E) 30 percent

Question 22

Figure 7.2
Assume 10⁹ E. coli cells/ml are in a flask.

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

Question 23

All of the following substances are effective against nonenveloped viruses EXCEPT

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

Question 24

An agent used to reduce the number of bacteria on a toilet would most accurately be called a(n)

A) virucide.
B) disinfectant.
C) fungicide.
D) antiseptic.
E) aseptic.

Question 25

Ethylene oxide

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

Question 26

Which of the following pairs is mismatched?

A) ultraviolet radiation - desiccation
B) supercritical fluids - CO₂
C) ionizing radiation - hydroxyl radicals
D) plasma sterilization - free radicals
E) ozone - takes electrons from substances

Question 27

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

A) the formation of a hypochlorite ion
B) the formation of hydrochloric acid
C) disruption of the plasma membrane
D) the formation of ozone
E) the formation of hypochlorous acid

Question 28

Which of the following chemical agents is used for sterilization?

A) alcohol
B) phenolics
C) soap
D) chlorine
E) ethylene oxide

Question 29

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)

In Table 7.3, which disinfectant was most effective against Salmonella?

A) K.O.
B) Sterl
C) Doom
D) Mortum
E) The answer cannot be determined based on the information provided.

Question 30

All of the following are effective for destroying prions EXCEPT

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

Question 31

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)

In Table 7.3, which disinfectant was bactericidal?

A) Doom
B) Sterl
C) K.O.
D) Mortum
E) The answer cannot be determined based on the information provided.

Question 32

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: $\begin{array} { l c } & \text { Bacteria/ml } \\\text { Cider only } & 2.2 \\\text { Cider with potassium sorbate } & 2.0 \\\text { Sodium benzoate } & 0 \\\text { Potassium sorbate } + \text { sodium benzoate } &0\end{array}$

-In Table 7.2, which preservative is most effective?

A) potassium sorbate
B) sodium benzoate
C) potassium sorbate + sodium benzoate
D) no preservative

Question 33

Which of the following does NOT achieve sterilization?

A) supercritical fluids
B) dry heat
C) ethylene oxide
D) pasteurization
E) autoclave

Question 34

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)

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.

Question 35

Which of the following pairs is mismatched?

A) alcohols - open wounds
B) H₂O₂ - open wounds
C) CuSO₄ - algicide
D) organic acids - food preservation
E) Ag - wound dressings

Question 36

Bone and tendons for transplant are decontaminated by

A) ethylene oxide.
B) plasma sterilization.
C) glutaraldehyde.
D) supercritical fluids.
E) peroxygens.

Question 37

All of the following are methods of food preservation EXCEPT

A) osmotic pressure.
B) microwaves.
C) high pressure.
D) ionizing radiation.
E) desiccation.

Question 38

Which of the following regarding antimicrobial control agents is FALSE?

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

Question 39

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

A) freezing
B) membrane filtration
C) dry heat
D) pasteurization
E) autoclave

Question 40

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.

In Figure 7.1, the thermal death point for this culture is

A) 15 minutes.
B) 50°C.
C) 170°C.
D) 30 minutes.
E) The answer cannot be determined based on the information provided

Question 41

An iodophor is a(n)

A) agent that reduces oxygen.
B) form of formaldehyde.
C) phenol.
D) iodine mixed with a surfactant.
E) quaternary ammonium compound.

Question 42

Desiccation is a reliable form of sterilization.

Question 43

Autoclaving is the most effective method of moist heat sterilization.

Question 44

Moist heat destroys organisms by denaturing proteins.

Question 45

Table 7.4
The results below were obtained from a use- dilution test of two disinfectants.
Cultures were inoculated into tubes with varying concentrations of disinfectants
and incubated for 24 hr at 20°C, then subcultured in nutrient media without disinfectants. (+ = growth; - = no growth)

In Table 7.4, what is the minimal bacteriostatic concentration of each disinfectant? Which compound is bactericidal? At what concentration?

Question 46

Some antimicrobial chemicals are considered to be disinfectants and antiseptics.

Question 47

Which of the following pairs of terms is mismatched?

A) sterilant - destroys all living microorganisms
B) bacteriostatic - kills vegetative bacterial cells
C) fungicide - kills yeasts and molds
D) germicide - kills microbes
E) virucide - inactivates viruses

Question 48

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

Question 49

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

Question 50

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

Question 51

Table 7.5
The following results were obtained from a use- dilution test of two disinfectants.
Cultures were inoculated into tubes containing varying concentrations of the disinfectants, incubated for 10 min. at 20°C, and then transferred to growth media without disinfectant. (+ = growth; - = no growth)

In Table 7.5, which disinfectant is most effective? Against which group of bacteria is Disinfectant A most effective?

Question 52

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

Question 53

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

Question 54

Why must most milk sold in the U.S. be refrigerated at all times while evaporated canned milk and milk in cardboard containers sold in Europe do not need to be refrigerated until they are opened?

Question 55

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