Question 1

Which of the following best describes a psychrotroph, and why are they significant in food microbiology?

Accepted Answer

They grow between 0°C and 20-30°C and are significant because they cause food spoilage at refrigeration temperatures.

Question 2

A bacterium is placed in a solution with a much higher salt concentration than its cytoplasm. What is the most likely outcome for the cell?

Accepted Answer

The cell will undergo plasmolysis due to water leaving the cell.

Question 3

Which of the following statements about agar is correct?

Accepted Answer

Agar liquefies at 100°C and solidifies at about 40°C, making it ideal as a solidifying agent in culture media.

Question 4

Which type of microorganism would most likely be responsible for spoilage of refrigerated foods?

Accepted Answer

Psychrotrophs

Question 5

A culture medium contains the following: glucose, ammonium phosphate, sodium chloride, magnesium sulfate, potassium phosphate, and water. This medium is best described as:

Accepted Answer

Chemically defined medium

Question 6

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 7

Which of the following is a trace element required by microbes, and what is its primary function?

Accepted Answer

Iron, which acts as an enzyme cofactor

Question 8

Which of the following best describes the growth pattern of microaerophiles in a thioglycolate broth tube?

Accepted Answer

Growth occurs in a thin layer just below the surface where oxygen concentration is low.

Question 9

Why are biofilms clinically significant in hospital settings?

Accepted Answer

Biofilms protect bacteria from antibiotics and the immune system, leading to persistent infections.

Question 10

Which of the following best describes an enriched medium, and when is it used?

Accepted Answer

A medium with extra organic growth factors; used for growing fastidious organisms such as Neisseria gonorrhoeae.

Question 11

A patient develops a bloodstream infection after receiving contaminated intravenous heparin. The contaminant is identified as Pseudomonas. Which microbial property most likely contributed to this outbreak?

Accepted Answer

Pseudomonas forms biofilms that protect it from disinfection.

Question 12

Which of the following best explains why the pH of culture media must be controlled during microbial growth?

Accepted Answer

Microbial metabolism often produces acids that can inhibit growth if not neutralized.

Question 13

Which of the following is true about facultative anaerobes?

Accepted Answer

They grow better in the presence of oxygen but can grow without it.

Question 14

Which of the following best describes the difference between complex and chemically defined media?

Accepted Answer

Complex media contain extracts and digests of natural products, while chemically defined media have known exact chemical compositions.

Question 15

Which of the following equations best represents the relationship between solute concentration and osmotic pressure?

Accepted Answer

$$\Pi = iMRT$$

Question 16

A microbe isolated from a hot spring in Yellowstone National Park grows optimally at 90°C. How would you classify this organism?

Accepted Answer

Hyperthermophile

Question 17

Which of the following best describes an aerotolerant anaerobe?

Accepted Answer

It does not use oxygen but is not harmed by its presence.

Question 18

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

Accepted Answer

NAD (nicotinamide adenine dinucleotide)

Question 19

Which of the following best explains why reducing media are used for culturing obligate anaerobes?

Accepted Answer

They contain chemicals like sodium thioglycolate that remove oxygen from the medium.

Question 20

Which of the following best describes the role of chemical signaling in biofilm formation?

Accepted Answer

It attracts bacteria to surfaces and coordinates gene expression for community behavior.

Microbial Growth: Physical and Chemical Requirements, Culture Media, and Biofilms

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