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calculations of cfu/ml - (Nov/27/2013 )

Hello all


I have already finished analysing all my samples for different types of bacteria.


So now i have calculated the cfu/ml for each dilution i.e. 1/10, 1/1000 and 1/100000  for bacteria in each sample, I have the cfu/ml of a selected bacteria for each of the dilution stated earlier. what is the next step? how can I interpret results when i have 3 values? do i take the average of  the 3 dilutions cfu values?? and present it or there is a way to do it and am not aware of?


I appreciate a lot your help and advice,




So how different are the values?  If you have done the experiment correctly, the values for each cfu calculation should be pretty similar, though counts from plates where the numbers of colonies are low (about 30 or fewer) get more and more inaccurate.  Ideally what you would do is choose a dilution and do that in triplicate, then average.


Many thanks for the reply!!


for example I had averaged the 1/1000 and 1/100000 counts since i had duplicates of each and I got 220 cell counts (1/1000) and 28 (1/100000)

220 28

  then i got the cfu/ml for each . so i choose from one of the dilutions if i understand you well??


Yes, I would go with the plate with a higher number of colonies, as this is more statistically accurate .


Folks typically take counts from plates of counts between ~25 and 250 (e.g. see )

-Phil Geis-

thankssssss you are always a great help in this forum!!