Question 1

Which phase of the microbial growth curve are bacteria most susceptible to antimicrobial agents, and why?

Accepted Answer

Log (exponential) phase, because cells are actively dividing and have high metabolic activity.

Question 2

A clinical sample is collected from a patient with a suspected bacterial infection. Why is it important to avoid contamination during collection, and what is a likely consequence if contamination occurs?

Accepted Answer

Contamination can lead to the growth of non-pathogenic organisms, making it difficult to identify the true pathogen.

Question 3

Which of the following best describes an obligate aerobe?

Accepted Answer

An organism that requires oxygen for growth and uses it as the final electron acceptor in respiration.

Question 4

A bacterium is found to grow equally well in the presence or absence of oxygen. Which term best describes its oxygen requirements?

Accepted Answer

Aerotolerant anaerobe

Question 5

Which of the following equations correctly represents the exponential (logarithmic) growth of a bacterial population, where $$N_t is $$the number of cells at time $$t$$, $$N_0 is $$the initial number of cells, and $$n is $$the number of generations?

Accepted Answer

$$N_t = N_0$ 	imes 2^n$$

Question 6

Which of the following is a key reason why most microorganisms have never been grown in any culture medium?

Accepted Answer

They require specific growth factors or conditions not provided in standard media.

Question 7

A patient is diagnosed with a Pseudomonas aeruginosa infection associated with a biofilm on a catheter. Which property of biofilms most contributes to the difficulty in treating this infection?

Accepted Answer

Biofilms protect bacteria from antibiotics and the immune system.

Question 8

Which of the following best explains why superoxide radicals ($$O_2$$^-$$) are toxic to cells?

Accepted Answer

They react with cellular components, causing oxidative damage.

Question 9

A microbiologist is culturing a bacterium that requires organic carbon and uses light as its energy source. Which term best describes this organism?

Accepted Answer

Photoheterotroph

Question 10

Which of the following statements about selective and differential media is correct?

Accepted Answer

Selective media favor the growth of particular microbes, while differential media distinguish between microbes based on metabolic reactions.

Question 11

A bacterium is classified as a mesophile. At which temperature range would you expect it to grow best?

Accepted Answer

20–40 $$^\circC$$

Question 12

Which of the following best describes the role of catalase in microbial cells?

Accepted Answer

Catalase breaks down hydrogen peroxide ($$H_2O_2) $$into water and oxygen.

Question 13

A bacterium isolated from acidic mine drainage grows optimally at pH 2. Which term best describes this organism?

Accepted Answer

Acidophile

Question 14

Which of the following is a growth factor for bacteria?

Accepted Answer

Amino acids that cannot be synthesized by the organism

Question 15

A facultative anaerobe is inoculated into a tube of thioglycollate broth. Where would you expect to see the most growth?

Accepted Answer

Mostly at the top, but growth throughout the tube

Question 16

Which of the following best explains why water is essential for microbial growth?

Accepted Answer

Water is required to dissolve enzymes and nutrients for metabolism.

Question 17

A hospital patient develops a lung infection after intubation. The infection is found to be caused by bacteria growing in a biofilm. Which of the following is NOT a characteristic of biofilms?

Accepted Answer

Biofilms make bacteria more susceptible to immune responses.

Question 18

Which of the following best describes the function of superoxide dismutase (SOD) in bacteria?

Accepted Answer

SOD converts superoxide radicals ($$O_2$$^-$$) to hydrogen peroxide (H_2O_2$).

Question 19

A bacterium is isolated from a hot spring and grows optimally at 70 $$^\circC. $$Which term best describes this organism?

Accepted Answer

Thermophile

Microbial Nutrition, Growth, and Biofilms: Study Notes for MIC 205

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