total bacterial count

chmc chmc at
Mon Apr 3 16:02:56 EST 2000

"Abdulhakim M. Abdi" wrote:

> Can anyone tell me how do you calculate the Total Bacterial Count:
> 1. If you have a plate count of between 30-300 colonies?

All you do is count up the colonies.  If you have, say 150 colonies,
then that means you had 150 bacteria.  If you plated 0.1 mL of your
bacterial suspension, and you had 10 mLs left, you would have 150
colonies/0.1 mLs = 1500 CFU's/mL x 10 mLs = 15000 bacteria.  If you
diluted your original suspension more than that, you will need to factor
that in as well.

> 2. If a plate count is less than 10 colonies per square centimeter?
> 3. If a plate count has more than 10 colonies per square centimeter?

If there are too many bacteria, you will have to dilute them, then
multiply by the amount you diluted them when you figure your TBC.  For
example, if you mixed 1 part bacterial suspension with 99 parts PBS or
water, you would have to mulitipy by 100 when you figure out the
original count.


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