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Drop plate technique - (Jul/18/2012 )

After making serial dilution and the solution will be plated out.

For example, I prepare dilution like this.


Change pipette tip when transferring mixtures to the next dilution in each step.
However, I'd like to know that Can I use the same pipette tip when plating out from high to low dilutions or not (from 10^-5 to 10^-1)? The number of bacteria will be the real number or not?

Thanks for answer.


In theory, yes, the addition of small amounts of diluted sample to a much more concentrated (10x in your case) shouldn't make much, if any difference to the more concentrated sample.


A general rule I always learned: from diluted to not diluted => same tip (goes for everything, not just microbiology)
From not diluted to diluted: change..

Its pretty easy to understand.

If you go from 10^-6 cells/ml to 10 cells/ml then why change a tip? You are not going to "add" cells in the 10 cells/ml

Other way around....

Same goes for chemical dilutions etc..