[Someone]

I don't know specifically about the ISS, but I found http://en.wikipedia.org/wiki/Tardigrade fascinating. Multicellular, and "can withstand temperatures from just above absolute zero to well above the boiling point of water, pressures about 6 times stronger than pressures found in the deepest ocean trenches, ionizing radiation at doses hundreds of times higher than would kill a person, and the vacuum of outer space. They can go without food or water for more than 10 years, drying out to the point where they are 3% or less water, only to rehydrate, forage, and reproduce."

It's "some of them will survive in outer space", though.