Thats kind of creepy, but check this out. I looked it up on Wikipedia and they say there are somewhere between 500 to 1000 different species of bacteria specialized to live in the human body, and everybody has about 10 bacteria cells living in them for every one of their own. They estimated we all have about 100 *trillion* bacteria cells floating around in us (vs about 10 trillion actual human cells).
Makes yogurt seem positively clean by comparison, doesn't it? Either way, most of them are symbiotes, so I guess its OK.