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.
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.
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.
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.
