Question 1

Which of the following best explains why psychrotrophs are a significant concern for food safety in medical microbiology?

Accepted Answer

They can grow at refrigeration temperatures and cause foodborne illness.

Question 2

A bacterium isolated from a hydrothermal vent with an optimum growth temperature above 80°C is classified as a:

Accepted Answer

Hyperthermophile

Question 3

Which of the following statements about Listeria monocytogenes is TRUE?

Accepted Answer

It can multiply at temperatures as low as 3°C, making it a risk in refrigerated foods.

Question 4

A culture medium that contains bile salts and crystal violet to inhibit Gram-positive bacteria, and lactose plus a pH indicator to distinguish lactose fermenters, is best described as:

Accepted Answer

Selective and differential medium

Question 5

Which of the following equations correctly represents the conversion of superoxide radicals to hydrogen peroxide and oxygen by superoxide dismutase?

Accepted Answer

$$2O_2^- + 2H^+ \rightarrow O_2$ + H_2O_2$$

Question 6

A bacterium that grows best at pH 1.5 and lyses at pH 5 is most likely a(n):

Accepted Answer

Obligate acidophile

Question 7

Which of the following best describes the stationary phase of a bacterial growth curve?

Accepted Answer

The rate of cell division equals the rate of cell death due to nutrient depletion or waste accumulation.

Question 8

Which of the following is a correct definition of generation time?

Accepted Answer

The time required for a cell to divide and its population to double.

Question 9

A bacterium that can grow in the presence or absence of oxygen, using aerobic respiration when oxygen is available and fermentation otherwise, is classified as a(n):

Accepted Answer

Facultative anaerobe

Question 10

Which of the following best explains why obligate anaerobes are harmed by oxygen?

Accepted Answer

They lack enzymes such as superoxide dismutase and catalase to detoxify reactive oxygen species.

Question 11

Which of the following best describes a chemoheterotroph?

Accepted Answer

An organism that obtains energy and carbon from organic compounds.

Question 12

Which of the following is a characteristic of agar that makes it useful as a solidifying agent in microbiological media?

Accepted Answer

It melts at 100°C and solidifies at 40°C, and is not metabolized by most bacteria.

Question 13

A bacterium that grows best in a medium with 7.5% NaCl and ferments mannitol, producing a yellow halo, is most likely being cultured on:

Accepted Answer

Mannitol Salt Agar, which is both selective and differential.

Question 14

Which of the following best describes the effect of a hypertonic environment on a bacterial cell?

Accepted Answer

Water leaves the cell, causing plasmolysis due to high osmotic pressure.

Question 15

Which of the following is NOT a typical growth factor required by bacteria?

Accepted Answer

Cholesterol

Question 16

A bacterial culture is inoculated into a fresh medium. For several hours, there is no increase in cell number, but cells are metabolically active and synthesizing new enzymes. This period is known as the:

Accepted Answer

Lag phase

Question 17

Which of the following best describes the role of catalase in aerobic bacteria?

Accepted Answer

It converts hydrogen peroxide into water and oxygen.

Question 18

A bacterium that grows best at pH 9.5 is classified as a(n):

Accepted Answer

Alkaliphile

Question 19

Which of the following best explains why secondary metabolites such as antibiotics are produced during the stationary phase of bacterial growth?

Accepted Answer

Nutrient limitation and waste accumulation trigger the production of compounds that inhibit competitors.

Microbial Growth: Physical and Chemical Requirements

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