Bacteria living on/in humans

[John Fekula]

My name is John Fekula and I am a pre-med student at Penn State.  I am 
currently working on a research paper about bacteria that have symbiotic 
relations with humans.  Can anybody give me information about bacteria which 
live on/in humans (ex. E. Coli, Streptococcus)?  The bacteria does not have to 
live exclusively on humans.  Any information will be
greatly appreciated.  Thank you in advance.

John Fekula
jdf142 at psu.edu