Final answer:
The formula to calculate CFUs/mL in the given scenario is A) CFU's × Dilution Factor × Volume Plated. This includes multiplying the number of colonies by the dilution factor and by the reciprocal of the volume of culture that was plated.
Step-by-step explanation:
To calculate CFUs/mL based on the provided scenario, the correct formula is CFU's × Dilution Factor × Volume Plated. When 50 colonies are counted on a plate from a 1:10,000 dilution, and only 0.1 mL of this dilution was plated, the calculation would be as follows:
CFU per mL = CFU's from the plate × Dilution Factor × reciprocal of the Volume Plated (since 0.1 mL is plated, we use 1/0.1 or 10 to get the volume in mL). So, we have CFUs/mL = 50 colonies × 10 (reciprocal of volume plated in mL) × 10,000 (dilution factor) = 5,000,000 CFUs/mL.
It is crucial to count plates that have between 30-300 colonies to ensure statistical reliability and accurate counting. Serial dilution is an important process that adjusts the cell density to a countable range, and the dilution factor accounts for the dilutions made in the culture to arrive at a workable concentration for the pour plate or spread plate methods. The dilution factor increases the accuracy of the cell density estimation.