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Exam 7: The Control of Microbial Growth

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Question 1

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Which concentration of ethanol is the most effective bactericide?

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

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

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Question 2

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

A) True
B) False

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Question 3

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One advantage of chemical plasma is that it ________ but a disadvantage is ________.

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

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?

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

All of the following are effective for destroying prions EXCEPT

Disinfection of water is achieved by all of the following EXCEPT

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?

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 hours 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?

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

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

Table 7.3 The following data were obtained by incubating gram-positive bacteria in nutrient medium + disinfectant for 24 hours,then transferring one loopful to nutrient medium (subculturing) .(+ = growth;- = no growth) -In Table 7.3,which disinfectant was bactericidal?

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

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

All of the following are methods of food preservation EXCEPT

Some antimicrobial chemicals are considered to be disinfectants and antiseptics.

Which of the following chemical agents is used for sterilization?

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

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