Q: A bacterial culture is grown for 2 hours, and during that time, it undergoes 6 generations of growth. What is the generation time for this bacterium? Use the formula $$\text{Generation time} = \frac{\text{Growth time (in minutes)}}{\text{Number of generations}}.$$

$$\text{Generation time} = \frac{120}{6} = 20$$ minutes

Question 1

Which of the following best describes the process of binary fission in bacteria?

Accepted Answer

A single cell divides into two genetically identical daughter cells after chromosome replication and septum formation.

Question 2

A bacterial culture is grown for 2 hours, and during that time, it undergoes 6 generations of growth. What is the generation time for this bacterium? Use the formula $$	ext{Generation time} = \frac{	ext{Growth time (in minutes)}}{	ext{Number of generations}}.$$

Accepted Answer

$$	ext{Generation time} = \frac{120}{6} = 20$$ minutes

Question 3

Which phase of the bacterial growth curve is characterized by a balance between cell division and cell death due to resource depletion and waste accumulation?

Accepted Answer

Stationary phase

Question 4

A hospital is experiencing persistent infections associated with indwelling catheters. Which microbial feature is most likely contributing to the difficulty in treating these infections?

Accepted Answer

Biofilm formation on catheter surfaces

Question 5

Which of the following best describes a mesophile?

Accepted Answer

A microbe that grows best at temperatures between 10–50$$^\circC$$, including most human pathogens.

Question 6

Which of the following statements about halophiles is correct?

Accepted Answer

Halophiles must maintain high concentrations of organic materials and ions in their cytoplasm to combat osmotic stress.

Question 7

Which type of microbe would you expect to find growing at the bottom of a thioglycolate broth tube, and why?

Accepted Answer

Obligate anaerobe, because it cannot tolerate oxygen.

Question 8

Which of the following best explains why actively growing bacterial cells are more susceptible to antibiotics that target cell wall synthesis?

Accepted Answer

Cell wall synthesis is most active during binary fission in the log phase.

Question 9

A laboratory technician needs to culture a fastidious organism. Which type of media should be used?

Accepted Answer

Complex media

Question 10

Which of the following is a correct pairing of a selective and differential medium with its function?

Accepted Answer

Mannitol salt agar: selects for salt-tolerant bacteria and differentiates based on mannitol fermentation.

Question 11

Which of the following methods would be most appropriate for sterilizing a heat-sensitive liquid?

Accepted Answer

Membrane filtration

Question 12

A sample is exposed to UV light to reduce microbial contamination. What is the primary mechanism by which nonionizing radiation kills microbes?

Accepted Answer

Formation of thymine dimers in DNA, leading to mutations

Question 13

Which of the following statements about disinfectants and antiseptics is correct?

Accepted Answer

Disinfectants are used on inanimate objects, while antiseptics are used on living tissue.

Question 14

Which of the following is the best definition of decimal reduction time ($$D$$ value)?

Accepted Answer

The time in minutes it takes to kill 90% of a microbial population at a set temperature.

Question 15

Which of the following chemical agents is classified as a high-level germicide and is used to sterilize heat-sensitive medical equipment?

Accepted Answer

Glutaraldehyde

Question 16

A patient sample is suspected to contain Mycobacterium tuberculosis. Which of the following disinfectants would be effective for decontamination?

Accepted Answer

A 2% solution of aqueous glutaraldehyde

Question 17

Which of the following best describes the function of surfactants in detergents?

Accepted Answer

They disrupt lipid membranes, increasing permeability and allowing other chemicals to enter the cell.

Question 18

Which of the following statements about the streak plate technique is correct?

Accepted Answer

It is used to isolate individual colonies from a mixed culture.

Question 19

Which of the following is a direct method for enumerating bacterial cells?

Accepted Answer

Viable plate count

Question 20

A laboratory is using PCR to identify a pathogen in a clinical sample. Which of the following best describes the advantage of PCR over traditional culturing methods?

Accepted Answer

PCR can detect and amplify DNA from microbes that cannot be cultured in the laboratory.

Fundamentals of Microbial Growth and Decontamination

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