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Exam 7: The Control of Microbial Growth

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Question 21

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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

F) B) and D)
G) A) and B)

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Question 22

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Which concentration of ethanol is the most effective bactericide?

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

F) B) and C)
G) B) and E)

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Question 23

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Which of the following pairs of terms is mismatched?

Autoclaving is the most effective method of moist heat sterilization.

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?

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?

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) $\begin{array} { l } \begin{array}{r}\text { Dilution } \\1: 16 \\1: 32 \\1: 64 \\1: 128\end{array}&\begin{array}{cc}{\text { Doom }} \\\hline \text { Initial } & \text { Subculture } \\- & + \\- & + \\- & + \\+ & +\end{array}&\begin{array}{cc}{\text { K.O. }} \\\hline \text { Initial } & \text { Subculture } \\+ & + \\+ & + \\+ & + \\+ & +\end{array}\\\\\begin{array}{r}\text { Dilution } \\1: 16 \\1: 32 \\1: 64 \\1: 128\end{array}&\begin{array}{cc}{\text { Mortum }} \\\hline \text { Initial } & \text { Subculture } \\- & - \\- & + \\+ & + \\+ & +\end{array}&\begin{array}{cc}{\text { sterl }} \\\hline \text { Initial } & \text { Subculture } \\+ & + \\+ & + \\+ & + \\+ & +\end{array}\end{array}$ -In Table 7.3, which disinfectant was bactericidal?

The following is true of quarternary ammonium compounds EXCEPT

Ethylene oxide

Which of the following regarding antimicrobial control agents is FALSE?

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

Moist heat destroys organisms by denaturing proteins.

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

All of the following substances are used to preserve foods EXCEPT

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

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) $\begin{array} { l } \begin{array}{r}\text { Dilution } \\1: 16 \\1: 32 \\1: 64 \\1: 128\end{array}&\begin{array}{cc}{\text { Doom }} \\\hline \text { Initial } & \text { Subculture } \\- & + \\- & + \\- & + \\+ & +\end{array}&\begin{array}{cc}{\text { K.O. }} \\\hline \text { Initial } & \text { Subculture } \\+ & + \\+ & + \\+ & + \\+ & +\end{array}\\\\\begin{array}{r}\text { Dilution } \\1: 16 \\1: 32 \\1: 64 \\1: 128\end{array}&\begin{array}{cc}{\text { Mortum }} \\\hline \text { Initial } & \text { Subculture } \\- & - \\- & + \\+ & + \\+ & +\end{array}&\begin{array}{cc}{\text { sterl }} \\\hline \text { Initial } & \text { Subculture } \\+ & + \\+ & + \\+ & + \\+ & +\end{array}\end{array}$ -In Table 7.3, which disinfectant was most effective against Salmonella?

All of the following substances are effective against nonenveloped viruses EXCEPT

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

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

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