
#1
Posted 25 April 2013 - 04:32 AM
First time I did the experiments the CFU results showed that 0.3 OD = 2.07 x 108 cells/ml.
After some weeks I did the same experiment and the CFU results are showed to me that 0.3 OD = 1.41 x 109 cells/ml.
I am not sure why I am getting that different values of CFU for same OD?
Any help will be highly appreciated. Thanks
#2
Posted 25 April 2013 - 07:13 AM
Did you do everything the same way? Same protocol?I have done CFU measurement of E.coli at OD~0.3. I am getting different results as describe below:
First time I did the experiments the CFU results showed that 0.3 OD = 2.07 x 108 cells/ml.
After some weeks I did the same experiment and the CFU results are showed to me that 0.3 OD = 1.41 x 109 cells/ml.
I am not sure why I am getting that different values of CFU for same OD?
Any help will be highly appreciated. Thanks
It can be because of so many things... Not the same amount of cells at the start... not the same time of incubation? Less or more aeration....
Also: in the end the difference is not that big...
If you don't know it, then ask it! Better to ask and look foolish to some than not ask and stay stupid.
#3
Posted 26 April 2013 - 04:26 AM
A log difference in cfu is rather significant to me.
#4
Posted 26 April 2013 - 04:33 AM
if the samples where the same yes.I agree there could be a ton of reasons why: viability caused by incubation time, media formulation, incubation temp, shaker speed....
A log difference in cfu is rather significant to me.
But here: since we dont know what might have gone "wrong" or different it means pretty much nothing.
Maybe I was not clear enough about that.
If you don't know it, then ask it! Better to ask and look foolish to some than not ask and stay stupid.
#5
Posted 27 April 2013 - 01:07 AM
Edited by Fiaq Khan, 27 April 2013 - 03:09 AM.
#6
Posted 27 April 2013 - 03:37 AM
#7
Posted 27 April 2013 - 04:21 AM
If you don't know it, then ask it! Better to ask and look foolish to some than not ask and stay stupid.
#8
Posted 01 May 2013 - 04:34 AM
http://www.microbiol..._.2011.17_3.pdf
#9
Posted 02 May 2013 - 05:31 AM
#10
Posted 04 May 2013 - 02:31 AM
How do you get that 0,5 log?USP (US Pharmacopeia) recognizes standard deviation of plate counts to be 0.5 log. How many plates were inoculated?
http://www.microbiol..._.2011.17_3.pdf
I see a standard deviation of 10-15%.
you do mean half a log difference?
Meaning 2.10^4 bacteria would still be the same as 2.10^3,5 bacteria? It seems a bit weird, because its 20000 bacteria compared with 6324.
#11
Posted 04 May 2013 - 08:33 AM
#12
Posted 04 May 2013 - 10:43 AM
It addresses only the method's capability.
Can you give a bit more explenation?
I am not sure if I understand you.
I also dont understand how you get that "standard deviation plate counts to be 0.5 log" from the paper you attached.
If I understand you correct you mean that the 0,5 log deviation is adressed to the method, so you mean that plating bacteria always has a 0,5 log deviation because of the plating?
And you do mean 10^-0,5 X + 0,5 , right? A half log difference?
#13
Posted 08 May 2013 - 06:39 AM
#14
Posted 08 May 2013 - 08:27 AM
Ok I see what you mean!Right.
Thanks
#15
Posted 08 May 2013 - 06:50 PM
Use a inoculating turntable, and an Ultrasonic bath(Jewelry Cleaner) to disociate bateria from each other.
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