Expert: Walter Hintz - 3/1/2008

Question
I am doing an experiment about germs in dog and human mouths. I used petri dishes, 2 for 2 dogs and 2 for 2 humans. I have red circles growing on both of the dog's petri dishes, and 1 large fuzzy brown circle on one of the human's and 1 small fuzzy circle that is white around the edge and greenish brown in the center. Do you know what types of germs they are? Do you know how I can find out?

Kristy

Answer
Hi Kristy; Without staining these colonies I can only make a guess.  The red colonies could be a species called Serratia.  The rough colonies are most likely Bacillus subtilis.  Both are common bacteria found in mouths.  Serratia can be harmful however so do not touch any colonies on the plates