bacterial growth curves and cell numbers

[am2lab]

Does anyone know if the numbers of cells at the same OD600s are different between different Escherichia coli strains (when they are grown under the same conditions), or are they same? I would think that the relationship between OD600 and numbers of cells would depend on cell size... Is that correct? Do I have to measure ODs and count cells for different strains or can I just do cell counts for one and measure ODs for all to know how many cells are there in the other strains? Please help!

[canalon]

They are different. Making a calibration of the OD is a good idea when working with different strains. However, unless working with very bizarre strains, the OD will give you a good idea of the cell number +/- 1 order of magnitude. It can be enough precision or not depending on what you want to do