Possible, but unlikely. They're pretty thorough about that kind of thing.![]()
Well, maybe but I remember watching the Apollo 11 crew making their way to their ship prior to launch:
http://www.apogeespacebooks.com/Titles Pics/FINALS/ap11crew.jpg
They walked in open air, anything could hitch a ride and no one would know. I don't suppose today's un-manned projects are any more scrupulous, or do they somehow sterilize, boil, burn, isolate every single component until it exits our atmosphere? I don't think so.
So, just supposing one of our miniscule bacterium is tougher than we know......