Expert: Walter Hintz - 1/13/2010

Question
How do I count bacteria colonies when doing the science project dealing with bacteria growth from human,cat and dogs mouths?

thank you

Answer
Hi Tyler
I assume you will grow the bacteria on a petri dish.  If there are not a lot of colonies there is no problem counting them all.  If you have a lot of them you can user a sampling method. Get some graph paper  and count the colonies in about ten squares picked at random.  Then determine the average number per square and multiply times the total of squares covered by the petri dish. You should remember that thee are different kinds of colonies and you should have different counts for the different types.  Also when you collect your data you have to describe the differences in the colonies