HI, Yes the data are from the same sample. The sample was serially diluted and 0.1 ml of the three consecutive dilutions (10 to the power 3 up to 10 to the power 5) were plated in three replications and incubated at 37oC for 48 hrs. My question is, it might be simple to calculate if only one dilution was plated. But here the figures are from three dilutions which gave us counts that are in the acceptable range (30-300) and we need to calculate CFU/ml of sample from the data. How can we consider the three dilutions for the calculation?
I assume this is a pour plate procedure. If so, it is preferable to use 1ml on plate.
As per my post 3 the data is "suspect" and probably better to repeat using 1ml.
However if cannot repeat, I suggest to apply this rule (Micro.examination of foods, da Silva, 2013) -
Rule 6 – Two consecutive dilutions with 25–250 colonies. Calculate the number of CFU of each dilution and compare the results.
6.a) If one of the results is greater than the double of the other, consider only the lower count
6.b) If one of the results does not exceed the double of the other, then both results must be considered, and the mean value should be presented as the final result
6a then gives a result of 2,200,000 CFU/gm [ ((205+210+250)/3) x 10^(4) ]
Edited by Charles.C, 11 March 2020 - 02:57 PM.