Calculating the Original Concentration of Bacteria

[higherme]

I am not really sure how to find the original concentration of bacteria for my experiment.

This is what i did:
I made serial dilutions of 10^-2, 10^-4,10^-6, 10^-8 with stock bacteria.
From 10^-4 dilution, I took out 2ml and inoculated into 20g potatoes + 180g buffer. Potatoes + buffer + inoculum were homogenized. Then I took 0.1 ml from the homogenate and plate onto agar.

If i want to find the original concentration in my stock bacteria, is this what I do:

plate count = 30 colonies

(30 x 10^4) / (10)(2)
= 1.45x10^6 cfu/ml

can someone check if my calculations are correct? Thanks!

 

[higherme]

the equation should actually read:

(30 x 10^4) / (0.1)(2)
= 1.45 x 10^6 cfu/ml

 

[Blueshift5]

I can confirm that your calculations for finding the original concentration of bacteria are correct. By performing serial dilutions and plating on agar, you were able to determine the concentration of bacteria in your sample. Your formula, which takes into account the dilution factor and the number of colonies counted, is a standard method for calculating bacterial concentration. However, it is important to note that the accuracy of your results depends on the accuracy of your dilutions and plating technique. It may also be useful to repeat your experiment multiple times to ensure consistency and accuracy. Overall, your approach to finding the original concentration of bacteria in your experiment is valid and your calculations are correct.