Question

Using a Neubauer chamber and microscopy, you count 10⁸ cells/mL in a tube of pond water.  However, from a dilution series and using the spread plate technique on nutrient agar, you calculate 10⁵ CFU/mL. Assuming both methods were done properly, what explanations could explain this discrepancy? (select all that apply)

		A proportion of the bacterial cells in the pond water are dead or viable but not culturable
		Some colonies grew but then disappeared from the plate before they were counted giving an incorrect count
		When plated on nutrient agar, a proportion of the bacterial cells swim to one another and merge to become one cell reducing the CFU count
		Nutrient agar does not support the growth of all bacterial cells in the pond water

Answer 1

The reason for the difference in the cell count could be because

*The proportion of the cells in the pond water are dead or viable but non culturable

*some colonies grew but then disappeared from the plate before they were counted giving an incorrect count

*when plated on nutrient Agar, a proportion of the bacterial cells swim to one another and merge to become one cell reducing the CFU Count.

*Nutrient Agar does not support the growth of all bacterial cells in the pond water

If more reasons are required, I'm mentioning it below.

*while doing the plating if pour plate or spread plate is used, there is a chance of cells gets adhered to the surface of the object which has used for the transfer

* if The dilution factor was not optimized, there is a chance of losing viable cells on each dilitions.

* There is a chance of releasing toxin from one colony which might inhibit other species of bacteria

* if different types of species are there, the time takes for each cell for the colony formation can vary

*during culturing, if the extrinsic factors are not favorable for any species, that cell will not be forming colony