a spread plate method yielded total of 75 colonies on 200ml

a spread plate method yielded total of 75 colonies on 200ml of pool water sample. How much bacteria are in a pool containing 5000 gallons. Assume that 4.5mL to a gallon. Show all calculations

Solution

Correction: It should be 4.5L and not 4.5mL to a gallon. The answer is given as per 4.5L to a gallon.

Answer

Total 75 colonies were found in 200 mLor 0.2L water sample

It implies that there are 75/0.2 colonies per liter

and (75/0.2)*4.5 colonies per gallon of water (Taking 1 gallon = 4.5L)

Therefore, one gallon of water will contain approximately 1,685 colony forming units (cfu) of bacteria