Hi,

I understand plating diluted bacterial concentrations and counting the colonies give out the CFU value.

But, how should I test the viability of bacterial samples with their initial concentration obtained from OD reading?

From my understanding, CFU is calculated by diluting an unknown concentration of the bacterial sample and plating them. So, if I know the initial concentration of the bacterial sample, isn't the CFU going to be about the same as the OD reading measurement? This is what confuses me.

If I have 3 samples with the same initial bacterial concentration, and want to check their viability, how should I check their viability? Is not the CFU going to be about the same for all three samples as they have the same initial bacterial concentration?

Please HELP. Thank you