Expert: Walter Hintz - 4/3/2007

Question
My son is in 5th grade and is doing a science project.  He chose "whose mouth has the most bacteria? A human, dog or cat.  We purchased petri dishes and swabbed the mouth of an inside dog, outside dog, inside cat, outside cat and a human  and also a human that had just brushed his teeth.  Where do we go from here.  It has been years and years since I had to do a science project and want to help him design his 3 fold board.  What type of information should we include.  Do we need to measure the bacterias spores?

Thank you in advance!

Answer
Hi Brigette
 I get a lot oof questions about the germ mouth projects. You must use the scientific method and the thing he must do state a problem and then make an educated guess as to what the answer is. The Problem here is "Whose mouth has the most bacteria?" Then you must have a hypothesis.( The educated guess) The Hypothesis could be: "The mouths of cats and dogs have more bacteria than a human mouth" You have too many variables here.  Forget the inside and outside pets and the mouth of a person with brushed teeth.  Stick with the mouth of a dog , a cat and a human.
You only need to do a quantitative study with this hypothesis. Your measurement and data will be the relative number of bacterial colonies on the plates. Try getting a rough colony count. (It would be a nice addition if observations were made about the variety of colonies.) If you are having problems doing let me know and I will tell you how to do it.
Take some photos of the plates, people and animals for the display board.  You must include on it everything that was done as well as the data.
 IMPORTANT. Mouths can contain dangerous bacteria so at no should any contact be made with the surface of the plate.  It is a good idea to tape it shut.
 Let me know how things are going.