A sample of ocean water is tested for its bacterial content in a plate count assay.A one-milliliter sample of the water is diluted in a 1:10 dilution series.0.1 milliliter of the second dilution tube is plated in a pour plate.After incubation,the plate has 191 colonies,indicating that the original water sample contained
A)191 cells per milliliter.
B)1,910 cells per milliliter.
C)19,100 cells per milliliter.
D)191,000 cells per milliliter.
E)1,910,000 cells per milliliter.

Question

Quizplus · Accepted Answer

The plate count assay gives an estimate of the number of viable bacterial cells present in a sample. In this case, a 1-milliliter sample of ocean water was diluted in a 1:10 dilution series, which means that each subsequent tube contains one-tenth of the bacteria present in the previous tube.

From the problem, we know that 0.1 milliliter of the second dilution tube was plated in a pour plate and after incubation, the plate has 191 colonies. To determine the number of cells present in the original sample, we can use the following equation:

Number of cells/mL = (number of colonies/0.1 mL plated) x (1/dilution factor)

In this case, the dilution factor is 10 because we diluted the original sample by a factor of 10 for each subsequent tube. Plugging in the values we have:

Number of cells/mL = (191/0.1) x (1/10) = 1910 cells/mL

However, we diluted the original sample by a factor of 10 twice, so we need to adjust our calculation by another factor of 10:

Number of cells/mL = 1910 x 10 x 10 = 191,000 cells/mL

Therefore, the correct answer is D.

A Sample of Ocean Water Is Tested for Its Bacterial