Q: During the log phase of a bacterial growth curve, the population doubles every 20 minutes. If you start with 1,000 cells, how many cells will there be after 1 hour? Use the formula $$N = N_0$ \times 2$$^{n}$$, where n$ is the number of generations.

$$N = 1,000 \times 2$$^{3}$$ = 8,000$$ cells

Question 1

A hospital is experiencing an outbreak of a bacterial infection. To prevent further spread, the staff must sterilize surgical instruments. Which method would be most effective for achieving sterilization, and why?

Accepted Answer

Using an autoclave at $$121^\circC $$and 15 psi for 15 minutes, because it destroys all forms of microbial life including spores.

Question 2

During the log phase of a bacterial growth curve, the population doubles every 20 minutes. If you start with 1,000 cells, how many cells will there be after 1 hour? Use the formula $$N = N_0$ 	imes 2$$^{n}$$, where n$ is the number of generations.

Accepted Answer

$$N = 1,000 	imes 2$$^{3}$$ = 8,000$$ cells

Question 3

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

Accepted Answer

Disinfection reduces microbes on inanimate surfaces, while antisepsis reduces microbes on living tissue.

Question 4

A patient is prescribed a broad-spectrum antibiotic. What is a potential risk associated with this treatment?

Accepted Answer

It can disrupt normal microbiota, increasing the risk of secondary infections such as Clostridioides difficile.

Question 5

Which environmental factor is most likely to limit the growth of an obligate aerobe in a sealed, oxygen-free container?

Accepted Answer

Lack of oxygen

Question 6

A laboratory technician uses a membrane filter with a pore size of $$0.22\ \mu m to $$sterilize a solution. Which type of microorganism is most likely to pass through the filter and contaminate the solution?

Accepted Answer

Viruses

Question 7

Which of the following best explains why heat is an effective method for microbial control?

Accepted Answer

Heat denatures proteins and disrupts cell membranes, leading to cell death.

Question 8

A patient develops a bacterial infection that is resistant to multiple antibiotics. Which of the following mechanisms most likely contributed to this resistance?

Accepted Answer

The bacteria acquired resistance genes through horizontal gene transfer.

Question 9

Which phase of the bacterial growth curve is characterized by a balance between cell division and cell death, resulting in a stable population size?

Accepted Answer

Stationary phase

Question 10

A microbiologist wants to determine the number of viable bacteria in a sample. Which method should they use, and why?

Accepted Answer

Plate count method, because only living cells form colonies on agar plates.

Question 11

Which of the following best describes the mechanism of action for penicillin?

Accepted Answer

Inhibits cell wall synthesis by blocking peptidoglycan cross-linking.

Question 12

A food processing plant uses UV radiation to treat surfaces. What is the primary effect of UV radiation on microbial cells?

Accepted Answer

It damages DNA by causing thymine dimers, inhibiting replication.

Question 13

Which of the following is a key reason why overuse of antibiotics in agriculture can contribute to the spread of antibiotic resistance in human pathogens?

Accepted Answer

Resistant bacteria can transfer resistance genes to human pathogens via horizontal gene transfer.

Question 14

A patient is treated with an antibiotic that inhibits protein synthesis. Which cellular structure is most likely targeted by this drug?

Accepted Answer

Ribosome

Question 15

Which of the following factors would most likely decrease the effectiveness of a chemical disinfectant in a hospital setting?

Accepted Answer

Presence of organic matter such as blood or pus.

Question 16

A culture medium contains glucose, peptone, and agar. Which component provides the primary carbon and energy source for most bacteria?

Accepted Answer

Glucose

Question 17

A patient with a wound infection is treated with iodine before surgery. What is the primary purpose of this treatment?

Accepted Answer

Antisepsis to reduce microbial load on living tissue

Question 18

Which of the following best explains why bacteria in the stationary phase are more resistant to antibiotics than those in the log phase?

Accepted Answer

Stationary phase cells have slowed metabolism and may express stress response genes.

Question 19

A clinical laboratory uses the Kirby-Bauer disk diffusion test to assess bacterial sensitivity to antibiotics. What does a large zone of inhibition around an antibiotic disk indicate?

Accepted Answer

The antibiotic is effective at inhibiting bacterial growth.

Question 20

A bacterium is found growing in hot springs at $$70^\circC $$and pH 2. Which term best describes its temperature and pH preferences?

Accepted Answer

Thermophile and acidophile

Microbial Growth, Control, and Antimicrobial Therapy: Study Notes

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