1) The number of single colonies on a correctly-prepared agar plate can be used
ID: 209509 • Letter: 1
Question
1) The number of single colonies on a correctly-prepared agar plate can be used to estimate the concentration of viable cells in a broth culture because:(Multiple Choice
A. The plate was inoculated with a known volume of culture.
B. Each colony contains only viable cells.
C. Each colony arises from a single viable cell.
A and B
A and C
2) A student needs to determine the concentration of viable cells in a broth culture of E.coli. What should they do? (Multiple Choice
Measure the optical density (OD) of the culture using a spectrophotometer.
Use a sterile spreader to spread a known volume of the culture across an agar plate.
Use a sterile loop to streak a small volume of the culture across an agar plate.
Perform serial dilutions of the culture, and then use a sterile spreader to spread a known volume of the dilutions across agar plates.
Perform serial dilutions of the culture, and then use a sterile loop to streak a small volume of the dilutions across agar plates.
If a bacterial broth culture has a concentration of 7.5x1011 cells/mL, what dilution is required to give a concentration of 3x104 cells/mL? (Multiple Choice
4.4*10-17 dilution
2.25*1016 dilution
4*1014 dilution
4*10-8 dilution
2.5*107 dilution
Explanation / Answer
1. A and B.
Colony forming unit consists of only viable cells.
2. Perform serial dilutions of the culture and then use a sterile spreader to spread a known volume of dilutions across the agar plate.
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