E coli CFUs - 48h incubation - silly Q! (Oct/21/2010 )
Hi everyone.
I plated out a serial dilution of E coli for CFU estimation as I normally would (serial dilution..LB plates), and incubated at 37C.
I incubated them for 48h instead of my normal 24 h (I forgot about them!!).. and so when I looked at the growth, there were large colonies there.
My question is can I count these as normal and trust the results?
After 48h incubation, would my 24h colonies just get bigger?
I know its a silly Q.. but I just need clarification so that I can trust my CFUs
Thanks, 
Yes, the colonies would just get bigger. The principle assumption that each colony arises from a single bacterium still holds true.
As long as your colonies are distinct and seperated from each other (ie not blobbing into each other making it hard to distinguish singles), then go ahead and count away.
leelee on Fri Oct 22 02:27:03 2010 said:
Yes, the colonies would just get bigger. The principle assumption that each colony arises from a single bacterium still holds true.
As long as your colonies are distinct and seperated from each other (ie not blobbing into each other making it hard to distinguish singles), then go ahead and count away.
Thanks very much for the clarification!!
At least I will be confident in my counts now...
Cheers