A 23-year-old woman has 10 Escherichia coli inoculated 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 of logarithmic growth, the total number of cells is
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?
The action of which of the following agents or processes on non-spore forming bacteria can be reversed?
(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 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 in vitro of (κ) 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 specimen of pasteurized goat’s milk is cultured for the presence of Brucella melitensis, an organism known to infect animals on an adjacent farm. The milk is declared safe to consume; however, some of those who consume it develop brucellosis. Which one of the following would best explain the disparity between the culture results and the patients’ illnesses?
(A) Bacteria in the milk were viable but not cultivatable
(B) Incomplete pasteurization of the milk
(C) The organisms in the milk were in the lag phase when tested
(D) The milk had a high level of a bactericidal antibiotic in it when tested
(E) There was posttest contamination of the milk
Working as a medical missionary in rural India, you spray the umbilicus of a newly born infant with a solution containing the chemical structure in the associated figure to prevent a tetanus infection. Which class of chemical agent does this structure belong?
(E) Quaternary ammonium class
Your superior requests that you sterilize some surgical instruments. Which one of the following agents would you use?
(B) Isopropyl alcohol (2%)
(D) Hydrogen peroxide (2%)
(E) Quaternary ammonium compound (2%)
The growth rate of bacteria during the maximum stationary phase of growth is
Chemical agents can interfere with the normal reaction between a specific enzyme and its substrate (chemical antagonism). Which one of the following inhibits energy-yielding cellular processes?
Which of the following is the most resistant to destruction by chemicals and heat?
(A) Spores of Aspergillus fumigatus
(B) Mycobacterium tuberculosis
(E) Spores of Bacillus anthracis