Antibacterial Assay - (May/25/2015 )

Hi all! 

I am seeking some advice on performing an antibacterial assay. What I plan to do as a preliminary experiment is to culture some E.coli to mid-exponential phase. Incubate it with my chosen antibacterial peptide for a period of time and plate them out to determine the CFU counts. My question is: 

- What strain of E. coli is normally used for antibacterial assays? ( We only have DH5alpha available, not sure if that is suitable)

- How do I go about determining the growth phase of E.coli. ( I have read that exponential growing bacteria have an absorbance of 0.5 at OD 600). 

Any comments will be much appreciated 

Exponential growth can be determined by plotting the OD600 over time, you'll soon see when the exponential growth happens.

No idea if DH5a is suitable for your assay though.