Expert: Walter Hintz - 1/10/2009

Question
How do I count the colonies in my dish?  Any other information that can help me in my science fair project.  

Answer
Hi Dallas;
Have you already performed this experiment or are about to.  Which is it. Either way you should change your hypothesis to something like "A dogs mouth contains more bacteria then a human mouth"
You should do so because a hypothesis is never a question.  Your problem is the question and the hypothesis is an educated guess as to to what the answer is. And the word cleaner is meaningless.
Now as to colony counting. Unless there are a lot of colonies it should be easy. If you have a lot of them do this. Get some graph paper and place it under the petri dish.( get some graph paper with squares of at least I/4 inch squares)  Pick ten squares ( or more) at random and count the colonies in each square. Find the average number of colonies per square. How many squares are covered by the dish? You cam measure this on the graph paper and then determine the total area covered under the dish.
For this study you should collect qualitative data. In other words describe the kinds of colonies ( color, size, shape etc.)
I believe you will find little difference in the mouth of a dog and a human.
 Let me know if you understood this.