Question 1

A clinical specimen suspected of containing Neisseria gonorrhoeae is being transported to the laboratory. Which of the following best explains why a CO$$_2-$$enriched atmosphere is used during incubation?

Accepted Answer

CO$$_2$$ enhances the growth of capnophilic and some fastidious organisms by providing a required growth factor.

Question 2

Which of the following best describes the main difference between phototrophs and chemotrophs?

Accepted Answer

Phototrophs use light as their main energy source, while chemotrophs obtain energy by oxidizing chemical substances.

Question 3

A laboratory technician is preparing media for a fastidious bacterium that requires hemin and NAD for growth. Which type of media should be used?

Accepted Answer

Enriched media

Question 4

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

Accepted Answer

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

Question 5

A patient sample is suspected to contain a halophilic microorganism. Which of the following best describes the growth conditions required for this organism?

Accepted Answer

High salt concentration in the medium

Question 6

Which of the following is a major nutritional requirement for all microorganisms and is the main structural element in carbohydrates, lipids, proteins, and nucleic acids?

Accepted Answer

Carbon

Question 7

A bacterium is classified as a facultative anaerobe. Which of the following best describes its oxygen requirements?

Accepted Answer

It can use oxygen when available but can also grow in its absence.

Question 8

A laboratory is culturing a microorganism that grows best at pH 3. Which term best describes this organism?

Accepted Answer

Acidophile

Question 9

Which of the following equations represents the catalase reaction that protects cells from hydrogen peroxide toxicity?

Accepted Answer

$$\mathrm{2H_2O_2 \rightarrow 2H_2O + O_2$}$$

Question 10

A clinical laboratory is attempting to recover a fastidious respiratory pathogen. Which of the following best explains why a delay in specimen transport could reduce recovery of the pathogen?

Accepted Answer

Fastidious organisms may die if exposed to unsuitable temperature, drying, or oxygen during transport.

Question 11

Which of the following best describes why high concentrations of sugar or salt can inhibit bacterial growth?

Accepted Answer

They reduce water availability by creating osmotic stress.

Question 12

A microorganism is able to grow in the presence of oxygen but does not use it for metabolism. Which term best describes this organism?

Accepted Answer

Aerotolerant anaerobe

Question 13

Which of the following trace elements is most likely to act as a cofactor for enzymes in microbial cells?

Accepted Answer

Iron (Fe)

Question 14

A patient is infected with a bacterium that grows best at 37$$^\circC $$and neutral pH. Which group does this organism most likely belong to?

Accepted Answer

Mesophiles

Question 15

Which of the following best explains why laboratory media are often buffered?

Accepted Answer

To maintain pH within the range required for optimal microbial growth

Question 16

A culture medium contains a high concentration of bile salts and crystal violet, inhibiting Gram-positive bacteria but allowing Gram-negative bacteria to grow. Which type of medium is this?

Accepted Answer

Selective medium

Question 17

Which of the following best describes the role of superoxide dismutase in microbial cells?

Accepted Answer

It converts superoxide radicals to hydrogen peroxide and oxygen.

Question 18

A laboratory is culturing a microorganism that requires both magnesium ions (Mg$$^{2+}) $$and potassium ions (K$$^+) $$for growth. What is the most likely function of these ions?

Accepted Answer

They act as enzyme cofactors and support ribosome and membrane function.

Question 19

A clinical laboratory is attempting to culture an obligate anaerobe from a wound specimen. Which of the following is the most important consideration for successful recovery?

Accepted Answer

Protect the specimen from exposure to oxygen during transport and culture.

Question 20

Which of the following best explains why no single growth factor acts alone in determining microbial growth?

Accepted Answer

Microbial growth depends on the combination of nutrients and environmental conditions; an organism may have adequate nutrients but fail to grow if temperature, pH, or oxygen is unsuitable.

Microbial Growth Factors: Nutrition, Physiology, Chemistry, and Environment

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