Microbial binding - (Mar/10/2009 )

Hi guys,

I am experimentingwith microbial(E.Coli O157 specifically)binding to a chemical molecule. When I check the O.D.600 before and after the treatment with this chemical, there seems to be some reduction compared to the control. However, CFU/ml doesn't look that different from the control in terms of being statistically significant. Does anyone have an idea Why O.D. and CFU do not seem to match?
Is one method more accurate than the other?
I've also look at it under the microscope and there is definately some binding although I am not sure if the binding is adequate to be shown by CFU/ml. /
Is there a commonly used method to observe cell interaction with a molecule?
I was thinking if hemocytometer will help.

Thanks in advance for any suggestions you might have.

If many cells are binding to one molecule, you will have some kind of aggregates, which would be detectable via OD.
But binding to the molecule doesn't mean killing the cell, right?
If you make dilutions for plating it out on Agar plates, also the chemical molecule gets diluted. And if the binding to the molecule is reversible or is at least a dynamic process with in which the equilibrium is pushed to bound state instead of the unbound (bound -><------unbound), more cells will go into the unbound state, and you will count more CFU.

Hope you understand what I mean....?

So, if that is the case, you should dilute the culture with media containing the same amount of the chemical molecule like you have in your culture.