Microorganisms and Disease - Exam Prep for Students

Microorganisms and Disease - Numerical Applications

Q. A culture shows a growth of 1,200 colonies after incubation. If the dilution factor was 1:100, what was the original concentration of bacteria in the sample?

A. 120,000 CFU/mL
B. 12,000 CFU/mL
C. 1,200 CFU/mL
D. 120 CFU/mL

Solution

To find the original concentration, multiply the number of colonies by the dilution factor: 1,200 colonies * 100 = 120,000 CFU/mL.

Correct Answer: A — 120,000 CFU/mL

Q. A laboratory test shows that a patient has a viral load of 5,000 copies/mL. If the treatment reduces the viral load by 80%, what is the new viral load?

A. 1,000 copies/mL
B. 2,000 copies/mL
C. 3,000 copies/mL
D. 4,000 copies/mL

Solution

An 80% reduction means that 20% of the original viral load remains. 20% of 5,000 copies/mL is 1,000 copies/mL.

Correct Answer: A — 1,000 copies/mL

Q. A patient is diagnosed with a bacterial infection and is prescribed antibiotics. If the bacteria have a resistance rate of 25%, what is the probability that a randomly selected bacterium is susceptible to the antibiotic?

A. 25%
B. 50%
C. 75%
D. 100%

Solution

If 25% of the bacteria are resistant, then 75% are susceptible to the antibiotic.

Correct Answer: C — 75%

Q. If a pathogen has a doubling time of 30 minutes, how many bacteria will be present after 3 hours starting from a single bacterium?

A. 8
B. 16
C. 32
D. 64

Solution

In 3 hours (180 minutes), there are 6 doubling periods (180/30). Starting from 1 bacterium, after 6 doublings, there will be 2^6 = 64 bacteria.

Correct Answer: D — 64

Q. If a pathogen has an ID50 of 500 organisms, how many organisms are needed to infect 50% of a population of 1,000 individuals?

A. 250
B. 500
C. 1,000
D. 1,500

Solution

The ID50 is the dose required to infect 50% of the population. Therefore, 500 organisms are needed to infect 50% of the population.

Correct Answer: B — 500

Q. If a patient has a bacterial load of 1,000,000 CFU/mL and a treatment reduces it by 99.9%, what is the remaining bacterial load?

A. 1 CFU/mL
B. 10 CFU/mL
C. 100 CFU/mL
D. 1,000 CFU/mL

Solution

A reduction of 99.9% means that 0.1% of the original load remains. 0.1% of 1,000,000 CFU/mL is 1,000 CFU/mL.

Correct Answer: A — 1 CFU/mL

Q. If a vaccine has a 90% success rate and is administered to 500 individuals, how many individuals are expected to remain unprotected?

A. 50
B. 100
C. 200
D. 300

Solution

With a 90% success rate, 10% will remain unprotected. 10% of 500 is 50 individuals.

Correct Answer: A — 50

Q. In a clinical trial, a vaccine shows a 70% efficacy rate. If 1,000 individuals are vaccinated, how many are expected to be protected?

A. 700
B. 300
C. 500
D. 900

Solution

With 70% efficacy, 70% of 1,000 individuals would be protected, which equals 700 individuals.

Correct Answer: A — 700

Q. In a study, 200 patients were infected with a virus. If 40% of them developed symptoms, how many patients showed symptoms?

A. 80
B. 60
C. 40
D. 20

Solution

40% of 200 patients is 0.4 * 200 = 80 patients who developed symptoms.

Correct Answer: A — 80

Q. What is the minimum inhibitory concentration (MIC) of a drug that inhibits 90% of a bacterial population at a concentration of 2 mg/L?

A. 1 mg/L
B. 2 mg/L
C. 3 mg/L
D. 4 mg/L

Solution

The MIC is defined as the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation. In this case, the MIC is 2 mg/L.

Correct Answer: B — 2 mg/L

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