Deck 7: The Control of Microbial Growth

Question 1

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

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

Answer 1

D

Question 2

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

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

Answer 2

D

Question 3

Which of the following pairs of terms is mismatched?

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

Answer 3

B

Question 4

Which of the following chemical agents is used for sterilization?

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

Question 5

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

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

Question 6

All of the following substances are effective against nonenveloped viruses EXCEPT

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

Question 7

Disinfection of water is achieved by all of the following EXCEPT

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

Question 8

Which of the following treatments is the most effective for controlling microbial growth?

A) 140°C for 4 seconds
B) 63°C for 30 minutes
C) 72°C for 15 seconds
D) They are equivalent treatments.
E) None of the answers is correct.

Question 9

Which concentration of ethanol is the most effective bactericide?

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

Question 10

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

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

Question 11

Which of the following regarding antimicrobial control agents is FALSE?

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

Question 12

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

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

Question 13

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

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

Question 14

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) gram-negative bacteria are often resistant to disinfectants.
D) invasive procedures can provide a portal of entry for bacteria.
E) None of the answers is correct; all of these factors may contribute to hospital -acquired infection.

Question 15

Which of the following does NOT achieve sterilization?

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

Question 16

Which of the following is a limitation of the autoclave?

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

Question 17

Oxidizing agents include all of the following EXCEPT

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

Question 18

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

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

Question 19

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

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

Question 20

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

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

Question 21

Table 7.1
A disk-diffusion test using Staphylococcus gave the following results: $$\begin{array} { c c } \text { Disinfectant } & \text { Zone of inhibition (mm) } \\\hline \text { A } & 0 \\\text { B } & 2.5 \\\text { C } & 10 \\\text { D } & 5\end{array}$$

-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.

Question 22

Table 7.1
A disk-diffusion test using Staphylococcus gave the following results: $$\begin{array} { c c } \text { Disinfectant } & \text { Zone of inhibition (mm) } \\\hline \text { A } & 0 \\\text { B } & 2.5 \\\text { C } & 10 \\\text { D } & 5\end{array}$$

-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.

Question 23

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, which is defined as the time to reduce a population by one log, is approximately

A) 40 minutes.
B) 30 minutes.
C) 0 minutes.
D) 10 minutes.
E) 60 minutes.

Question 24

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 $/ \mathrm { ml }$
$\begin{array}{ll}\text { Cider only } & 2.2 \\\text { Cider with potassium sorbate } & 2.0 \\\text { Sodium benzoate } & 0 \\\text { Potassium sorbate + sodium benzoate } & 0\end{array}$ In Table 7.2, which preservative is most effective?

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

Question 25

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)
$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { Doom }$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { K.O. }$
$\begin{array}{rcccc}\text { Dilution } & \text { Initial } & \text { Subculture } & \text { Initial } & \text { Subculture } \\1: 16 & - & + & + & + \\1: 32 & - & + & + & + \\1: 64 & - & + & + & + \\1: 128 & + & + & + & +\end{array}$

$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { Mortum }$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { Sterl }$
$\begin{array}{rcccc}\text { Dilution } & \text { Initial } & \text { Subculture } & \text { Initial } & \text { Subculture } \\1: 16 & - & - & - & + \\1: 32 & - & + & + & + \\1: 64 & + & + & + & + \\1: 128 & + & + & + & +\end{array}$

-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.

Question 26

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

Question 27

Which of the following regarding antimicrobial control agents is FALSE?

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

Question 28

Table 7.1
A disk-diffusion test using Staphylococcus gave the following results: $$\begin{array} { c c } \text { Disinfectant } & \text { Zone of inhibition (mm) } \\\hline \text { A } & 0 \\\text { B } & 2.5 \\\text { C } & 10 \\\text { D } & 5\end{array}$$

-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.

Question 29

Ethylene oxide

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

Question 30

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.
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 31

An iodophor is a(n)

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

Question 32

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.
Which of the following pairs is mismatched?

A) organic acids  food preservation
B) Ag  wound dressings
C) alcohols  open wounds
D) CuSO4  algicide
E) H₂o₂  open wounds

Question 33

Which of the following pairs is mismatched?

A) ionizing radiation  hydroxyl radicals
B) ultraviolet radiation  desiccation
C) supercritical fluids  Co₂
D) plasma sterilization  free radicals
E) ozone  takes electrons from substances

Question 34

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

Question 35

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 36

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 37

All of the following substances are used to preserve foods EXCEPT

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

Question 38

All of the following are effective for destroying prions EXCEPT

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

Question 39

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)
$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { Doom }$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { K.O. }$
$\begin{array}{rcccc}\text { Dilution } & \text { Initial } & \text { Subculture } & \text { Initial } & \text { Subculture } \\1: 16 & - & + & + & + \\1: 32 & - & + & + & + \\1: 64 & - & + & + & + \\1: 128 & + & + & + & +\end{array}$

$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { Mortum }$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { Sterl }$
$\begin{array}{rcccc}\text { Dilution } & \text { Initial } & \text { Subculture } & \text { Initial } & \text { Subculture } \\1: 16 & - & - & - & + \\1: 32 & - & + & + & + \\1: 64 & + & + & + & + \\1: 128 & + & + & + & +\end{array}$

-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 40

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)
$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { Doom }$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { K.O. }$
$\begin{array}{rcccc}\text { Dilution } & \text { Initial } & \text { Subculture } & \text { Initial } & \text { Subculture } \\1: 16 & - & + & + & + \\1: 32 & - & + & + & + \\1: 64 & - & + & + & + \\1: 128 & + & + & + & +\end{array}$

$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { Mortum }$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { Sterl }$
$\begin{array}{rcccc}\text { Dilution } & \text { Initial } & \text { Subculture } & \text { Initial } & \text { Subculture } \\1: 16 & - & - & - & + \\1: 32 & - & + & + & + \\1: 64 & + & + & + & + \\1: 128 & + & + & + & +\end{array}$

-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.

Question 41

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 42

Some antimicrobial chemicals are considered to be disinfectants and antiseptics.

Question 43

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

Question 44

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

Question 45

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

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

Question 46

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

A) supercritical Co₂
B) filtration
C) desiccation
D) ionizing radiation
E) lyophilization

Question 47

Desiccation is a reliable form of sterilization.

Question 48

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 49

Moist heat destroys organisms by denaturing proteins.

Question 50

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

Question 51

Bone and tendons for transplant are decontaminated by

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

Question 52

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

Question 53

How is hydrogen peroxide antimicrobial?

Question 54

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

Question 55

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

Question 56

The following is true of quarternary ammonium compounds EXCEPT

A) they are non-toxic at lower concentrations.
B) they are effective when combined with soaps.
C) they are tasteless.
D) they may be an ingredient in mouthwash.
E) they are stable.

Question 57

Assume that you are responsible for decontaminating materials in a large hospital. How would you sterilize each of the following? Briefly justify your answers.
a. a mattress used by a patient with bubonic plague
b. intravenous glucose-saline solutions
c. used disposable syringes
d. tissues taken from patients

Question 58

All of the following are methods of food preservation EXCEPT

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

Question 59

Autoclaving is the most effective method of moist heat sterilization.

Question 60

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

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

Question 61

What are the advantages of gluteraldehyde compared to formaldehyde?

Question 62

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 63

List the microbial targets of disinfecting chemicals and provide one example of a chemical agent that affects that structure.