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Exam 6: Microbial Growth

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Question 21

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Most fungi grow best at pH

A) 7.
B) 1.
C) 14.
D) 5.
E) 9.

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Question 22

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An isolated colony on a streak plate contains millions (or even billions) of identical cells all arising from one initial cell.

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Question 23

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Salts and sugars work to preserve foods by creating a

Which of the following is the best definition of generation time?

The biosafety level (BSL) for most introductory microbiology laboratories is

Which of the following is an advantage of the standard plate count?

A sample of milk is tested for its bacterial content in a plate count assay. A one -milliliter sample of the milk is diluted in a 1:10 dilution series. One milliliter of the third dilution tube is plated in a pour plate. After incubation, the plate has 54 colonies, indicating that the original milk sample contained

Table 6.1 Three different culture media are shown below. $\begin{array}{|l|l|l|}\hline \text { Medium A } & \text { Medium B } & \text { Medium C } \\\hline \text { Na2H PO4 } & \text { Tide detergent } & \text { Glucose } \\\hline \text { KH2PO4 } & \text { Na2HPO4 } & \text { Peptone } \\\hline \mathrm{MgSO}_{4} & \mathrm{KH}_{2} \mathrm{PO}_{4} & \left(\mathrm{NH}_{4}\right) _{2} \mathrm{SO}_{4} \\\hline \mathrm{CaCl}_{2} & \mathrm{MgSO}_{4} & \mathrm{KH}_{2} \mathrm{PO}_{2} \\\hline \mathrm{NaHCO}_{3} & \left(\mathrm{NH}_{4}\right) _{2} \mathrm{SO}_{4} & \mathrm{Na}_{2} \mathrm{HPO}_{4} \\\hline\end{array}$ -For the three types of media in Table 6.1, which medium (or media) is/are chemically defined?

In one hospital, Pseudomonas aeruginosa serotype 10 infected the biliary tract of 10 percent of 1300 patients who underwent gastrointestinal endoscopic procedures. After each use, endoscopes were washed with an automatic reprocessor that flushed detergent and glutaraldehyde through the endoscopes, followed by a tap water rinse. P. aeruginosa serotype 10 was not isolated from the detergent, glutaraldehyde, or tap water. What was the source of the infections?

Most pathogenic bacteria are thermophiles.

Figure 6.2 -Figure 6.2 shows a typical bacterial growth curve with the y-axis indicating the log of the number of bacteria and the x-axis indicating time in culture. In the figure, which section (or sections) shows a growth phase where the number of cells dying equals the number of cells dividing?

During which growth phase will gram-positive bacteria be most susceptible to penicillin?

Which of the following is NOT a direct method to measure microbial growth?

Filtration methods, followed by growth of the bacteria trapped on the filters in growth media, are used to count bacteria present in very low concentrations, such as in lakes and streams.

Which of the following is an example of a metabolic activity that could be used to measure microbial growth?

Which of the following is an organic growth factor?

Laboratory cultivation of obligate anaerobes requires reducing media or special growth chambers filled with inert gases.

The addition of which of the following to a culture medium will neutralize acids?

The source of nutrients in nutrient agar is

Nitrogen-fixing bacteria, such as cyanobacteria, can use atmospheric nitrogen (N2) for their nitrogen source.