One thing that becomes more clear with each piece of research is that the human body is a hive of mostly harmless bacteria that live in any crevice they can reach while affecting their human host as little as possible. In some cases these bacteria can be very beneficial – preventing more dangerous bacteria from taking up residence in places like the stomach and throat. In some cases they can occasionally go rogue, get into places they shouldn’t be, and cause havoc.
Click "source" to read more.