Question

You are studying the bacteria in the water of a nearby pond. From a 100 mL sample, you use a 0.5 mL subsample to inoculate a plastic dish filled with a semi solid nutrient medium that fosters growth of coliform bacteria. After an appropriate incubation period, you count 100 bacterial colonies growing on the surface of the medium. What conclusion can you make about the coliform bacteria in the pond water

Answer 1

There are 20,000 colony forming units of coliform per 100 mL of the pond water.

Step-by-step explanation:

0.5 mL of the 100 mL sample was inoculated.

There were 100 colonies in the 0.5 mL of the sample.

Hence, the number of colonies that would be in the 100 mL can be calculated as:

100 colonies = 0.5 mL

x = 100 mL

x = 100 x 100/0.5

= 20,000 colonies

Hence, the conclusion that can be made is that there were 20,000 CFU (colony forming units) of coliform bacteria in a 100 mL sample of the pond water.