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Chapter 4. Growth, Survival, and Death of Microorganisms

A 23-year-old woman has 10 E. coli introduced into her bladder while having sex. This organism has a generation time of 20 minutes. After a lag of 20 minutes, the E. coli enter the logarithmic phase of growth. After 3 hours, the total number of cells is

(A) 2056

(B) 5012

(C) 90

(D) 1028

(E) 1,000,000

A 73-year-old woman is admitted to the hospital for intravenous treatment of an abscess caused by Staphylococcus aureus. Subsequent to her treatment and discharge from the hospital, it is necessary to disinfect the hospital room. One thousand of the S. aureus cells are exposed to a disinfectant. After 10 minutes, 90% of the cells are killed. How many cells remain viable after 20 minutes?

(A) 500

(B) 100

(C) 10

(D) 1

(E) 0

The action of which of the following agents or processes on non-spore forming bacteria can be reversed?

(A) A disinfectant

(B) A bactericidal agent

(C) A bacteriostatic agent

(D) Autoclaving at 121°C for 15 minutes

(E) Dry heat at 160–170°C for 1 hour

The growth rate of bacteria during the exponential phase of growth is

(A) Zero

(B) Increasing

(C) Constant

(D) Decreasing

(E) Negative

A physician obtains a sputum specimen from a patient suffering from tuberculosis. This sputum sample contains one viable Mycobacterium tuberculosis, an organism with a slow doubling time in vitro of 48 hours, which corresponds to a growth rate constant (k) in vitro of 0.04 h-1. Estimating that the biomass of this single mycobacterial organism is 2.3 × 10−13 g and assuming that this organism is immediately going to enter log phase growth, how many hours will it take to produce 10−6 g of biomass?

(A) 4 hours

(B) 40 hours


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