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Exam 7: The Control of Microbial Growth

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Question 21

True/False

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

A) True
B) False

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Question 22

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Disinfection of water is achieved by all of the following EXCEPT

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

F) C) and D)
G) B) and C)

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Question 23

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Which of the following pairs is mismatched?

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?

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

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

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?

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

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?

Which concentration of ethanol is the most effective bactericide?

Some antimicrobial chemicals are considered to be disinfectants and antiseptics.

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

Oxidizing agents include all of the following EXCEPT

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

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

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?

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?

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

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?

Which of the following regarding antimicrobial control agents is FALSE?