Question

I m doing an experiment where I have to calculate cfu/ml of bacteria grown on LB agar plates and I have to calculate cfu/ml. I know I have to add x ml amount of bacterial culture to x ml amount of medium and dilute the samples, but how do i measure the amount of bacterial culture by ml? If the control bacteria is growing on a solid LB agar plate, how do I make the dilution medium and measure the amount of bacteria that I took off of the plate?

Answer 1

you dont need to measure the amount of bacterium before taking from the plate. Just take a colony and try placing them in 1 mL of media or PBS.

from this 1mL u need to make serial dilutions such that take 100uL of media after proper mixing of cells and place them in fresh 900uL of media and mix again properly. Then take 100uL from this sample and add to 900uL of fresh media and mix again. follow this step 7-8 times to get to 10^-8 dilution.

then add 100uL from the final tube to your plate and spread the cells to observe and count the number of colonies next day.

whatever number u find, multiply it with the dilution factor i.e 10⁸ to get the number of cells in the original volume.

Thank you.