Q: A bacterial culture is grown for 6 hours, and the generation time is 30 minutes. How many generations have occurred?

$$n = \frac{t}{g} = \frac{6 \ \text{hours} \times 60 \ \text{min/hour}}{30 \ \text{min}} = 12$$

Question 1

A hospital laboratory is attempting to isolate Staphylococcus aureus from a wound sample. Which type of medium would be most appropriate to both select for Staphylococcus species and differentiate S. aureus from other staphylococci, and why?

Accepted Answer

A selective and differential medium, such as Mannitol Salt Agar, because it inhibits non-staphylococci and differentiates S. aureus by mannitol fermentation.

Question 2

Which of the following best describes a fastidious microbe?

Accepted Answer

A microbe that requires specific and complex nutritional or environmental factors for growth.

Question 3

A bacterial culture is grown for 6 hours, and the generation time is 30 minutes. How many generations have occurred?

Accepted Answer

$$n = \frac{t}{g} = \frac{6 \ 	ext{hours} 	imes 60 \ 	ext{min/hour}}{30 \ 	ext{min}} = 12$$

Question 4

Which of the following best describes the lag phase of a bacterial growth curve?

Accepted Answer

Cells are adapting to the environment and preparing for active division, but not yet dividing rapidly.

Question 5

A microbiologist wants to count the number of viable bacteria in a water sample. Which method would be most appropriate and why?

Accepted Answer

Plate count method, because only viable cells will form colonies.

Question 6

Which of the following statements about phototrophs and chemotrophs is correct?

Accepted Answer

Phototrophs use light as their energy source, while chemotrophs obtain energy from chemical compounds.

Question 7

A sample contains $$1 	imes 10^6$ bacteria per mL. You perform a serial dilution by transferring 1 mL of the sample into 9 mL of sterile diluent, and repeat this process three times. What is the final dilution factor?

Accepted Answer

$$1:1000$$

Question 8

Which of the following best describes the difference between sterilization and disinfection?

Accepted Answer

Sterilization kills all forms of microbial life, including spores; disinfection eliminates most pathogens but not necessarily spores.

Question 9

A patient sample is collected for microbiological analysis. Which of the following is NOT a critical consideration in collecting clinical samples?

Accepted Answer

Allowing the sample to sit at room temperature for several hours before processing.

Question 10

Which of the following is an example of a bacteriostatic agent?

Accepted Answer

An agent that inhibits bacterial growth without killing them.

Question 11

A microbiologist is using MacConkey agar to isolate bacteria from a stool sample. What is the primary function of this medium?

Accepted Answer

It is a selective and differential medium that inhibits Gram-positive bacteria and differentiates lactose fermenters.

Question 12

Which of the following is a correct calculation for the number of bacteria in the original sample if 0.1 mL of a $$1:1000$$ dilution yields 50 colonies on a plate?

Accepted Answer

$$	ext{CFU/mL} = \frac{	ext{colonies}}{	ext{volume plated} 	imes 	ext{dilution factor}} = \frac{50}{0.1 	imes 1/1000} = 500,000$$

Question 13

Which of the following best describes binary fission?

Accepted Answer

A process in which a single cell divides into two identical daughter cells.

Question 14

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

Accepted Answer

Counting colonies on an agar plate after serial dilution.

Question 15

Which of the following statements about germicides is correct?

Accepted Answer

High-level germicides can kill all microbes, including spores, with sufficient exposure time.

Question 16

A bacterium is classified as a mesophile. Which of the following best describes its optimal growth temperature?

Accepted Answer

Between $$20^\circC $$and $$45^\circC$$

Question 17

Which of the following is a key consideration when selecting a chemical germicide for use in a hospital setting?

Accepted Answer

The ability of the germicide to sterilize in the presence of organic matter.

Question 18

Which of the following best describes an obligate anaerobe?

Accepted Answer

A microbe that is killed by exposure to oxygen.

Question 19

Which of the following is the correct formula to calculate the number of generations ($$n) $$given the initial number of cells ($$N_0) $$and the final number of cells ($$N$$)?

Accepted Answer

$$n = \log_2$ \left( \frac{N}{N_0$} \right)$$

Question 20

Which of the following is a correct statement about differential media?

Accepted Answer

Differential media contain indicators that reveal differences between bacterial species based on metabolic reactions.

Fundamentals of Microbial Growth and Control – Study Guide (Module 5)

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