Question

In theory, the direct cell count and the total heterotrophic plate count are providing a measure of ‘all’ the bacteria present. Answer both parts a and b: a. Do the two methods yield a similar result? Which method yielded the higher count? b. Are the results as you would expect? Justify your answer

The results were not similar, with the direct cell count being much higher. I don't really know why??

Answer 1

a) Both methods do not yield same result.The number of colonies in the Direct Cell Count Plate would be higher most probably.

It may vary according to the test conditions in the Heterotrophic plate count.

b)Direct counting methods are used to determine bacterial concentration without the need for advanced equipment.
Direct counting methods include microscopic counts using a hemocytometer or a counting chamber. The hemocytometer works by creating a volumetric grid divided into differently sized cubes for accurately counting the number of particles in a cube and calculating the concentration of the entire sample.

As with hemocytometers or counting chambers, cultures need to be heavily diluted prior to plating. Otherwise, instead of obtaining single colonies that can be counted, of thousands of colonies will form, all lying atop of each other.

Due to heavy dilution we get maximum number of single colonies

The heterotrophic plate count (HPC), formerly known as the standard plate
Colonies may arise from pairs, chains, clusters, or single cells all of which are included in the term colony-forming units (CFU).

So the number colonies might not be exact always in Heterotrophic plate count.

HPC test methods involve a wide variety of test conditions that lead to a wide range of quantitative and qualitative results. Temperatures employed range from around 20 °C to 40 °C, incubation times from a few hours to seven days or a few weeks, and nutrient conditions from
low to high. The test itself does not specify the organisms that are detected.

The count of colonies depend on these test conditions.

So Total Heterotrophic Plate count does not provide actual count but its count can be used as an indicator.