We are now eight hours into the experiment. I've taken fifteen samples so far - now it's your turn. Here's what you need to do:
Viable Count:
Since you have little idea of the number of viable bacteria in your culture you need to make several dilutions and hope to plate out a dilution giving the appropriate number of colonies. When counting bacterial colonies it is best to have about 100 colonies on a plate. Why?
Make the appropriate ten-fold dilutions:
Set up 6 tubes containing 0.9 ml of sterile water.
Using a pipette with a sterile tip, aseptically transfer 0.1 ml of your culture into the first tube (10-1 dilution). Discard the tip.
Mix well and using a fresh pipette tip, transfer 0.1 ml to the next dilution tube (10-2 dilution). Discard pipette tip.
Proceed in this way with your dilutions down to 10-6.
Using a fresh pipette tip and starting with the highest dilution, take 0.1 ml of suspension and transfer it to the surface of an agar plate.
Take a spreader and spread out your bacterial dilution over the whole surface of the plate.
Once dry, place the plates in appropriate box for incubation at 37°C.
