Question 1

Which of the following best describes the optimum growth temperature for mesophilic bacteria?

Accepted Answer

Between $$25^{\circ}C$ and 40$$^{\circ}$$C$$

Question 2

A food microbiologist isolates bacteria from spoiled orange juice (pH 5). Which type of bacteria is most likely to thrive in this environment?

Accepted Answer

Acidophiles

Question 3

Which equation correctly represents the total number of cells after $$n$$ generations if the initial population is one cell and the cells divide by binary fission?

Accepted Answer

$$2^n$$

Question 4

A bacterium that grows only at the bottom of a thioglycollate broth tube and is killed by atmospheric oxygen is classified as:

Accepted Answer

Obligate anaerobe

Question 5

Which enzyme catalyzes the conversion of superoxide radicals to hydrogen peroxide and oxygen?

Accepted Answer

Superoxide dismutase (SOD)

Question 6

A hospital patient develops an infection from a biofilm on a catheter 300 days after exposure to contaminated heparin. What property of biofilms most likely contributed to this delayed infection?

Accepted Answer

Biofilms are 1000x more resistant to microbicides

Question 7

Which of the following best describes a chemically defined medium?

Accepted Answer

Exact chemical composition is known

Question 8

A microbiologist wants to isolate a bacterium capable of degrading phenol from a soil sample containing thousands of other bacteria. Which technique should be used?

Accepted Answer

Enrichment culture

Question 9

Which of the following is a trace element required in small amounts, usually as an enzyme cofactor?

Accepted Answer

Iron

Question 10

Which phase of the bacterial growth curve is characterized by intense metabolic activity but no increase in cell number?

Accepted Answer

Lag phase

Question 11

A water sample is filtered through a membrane, which is then placed on a selective medium. After incubation, 214 colonies are counted. What is the bacterial concentration in the original 100 mL sample?

Accepted Answer

214 bacteria/100 mL

Question 12

Which of the following best describes the function of reducing media?

Accepted Answer

To cultivate obligate anaerobes by removing oxygen

Question 13

Which of the following is NOT a direct method for measuring microbial growth?

Accepted Answer

Turbidity

Question 14

A microbiologist streaks a plate to isolate pure cultures. What is the expected result after proper streaking and incubation?

Accepted Answer

Individual colonies arising from single cells

Question 15

Which of the following best explains why food stored in a deep container cools more slowly and is more prone to Bacillus cereus growth than food stored in a shallow container?

Accepted Answer

Deep containers retain heat longer, keeping food in the danger zone ($$15^{\circ}C$ to 43$$^{\circ}$$C) $$for longer

Question 16

Which of the following best describes the difference between selective and differential media?

Accepted Answer

Selective media suppress unwanted microbes; differential media distinguish between different microbes

Question 17

A bacterium is described as a facultative anaerobe. Which of the following best describes its growth pattern in a tube of solid growth medium?

Accepted Answer

Growth throughout the tube, with more growth at the top

Question 18

Which of the following is an organic growth factor required by some bacteria?

Accepted Answer

Thiamine

Question 19

A laboratory is working with a newly discovered virus that is highly contagious and lethal. Which biosafety level (BSL) is required for this work?

Accepted Answer

BSL-4

Question 20

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

Accepted Answer

Water leaves the cell, causing plasmolysis

Microbial Growth: Requirements, Culture Media, and Measurement

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