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