Question

0.2 mls of a 10⁻⁴ dilution of a virus preparation yields 90 plaques. What is the number of PFU per ml in the undiluted virus preparation?

1) 9.0 × 10⁵
2) 4.5 × 10⁶
3) 4.5 × 10⁷
4) 9.0 × 10⁸

Answer 1

To calculate the number of plaque-forming units (PFU) per ml in the undiluted virus preparation, multiply the number of plaques by the reciprocal of the volume plated and by the reciprocal of the dilution factor. The answer for the given scenario is 4.5 × 10⁶ PFU/mL.

Step-by-step explanation:

The student asked how to calculate the number of plaque-forming units (PFU) per ml in the undiluted virus preparation if 0.2 mls of a 10⁻⁴ dilution yields 90 plaques. To find the PFU/mL in the undiluted virus preparation, multiply the number of plaques by the reciprocal of the volume plated (which will convert the volume to 1 ml) and then by the reciprocal of the dilution factor.

Using the given numbers, the calculation is as follows: PFU/mL = 90 plaques / 0.2 mL × 10⁴ = 450 plaques/mL × 10⁴ = 4.5 × 10⁶ PFU/mL. Thus, the correct answer to the student's question is option 2) 4.5 × 10⁶.