Food is ubiquitous. All organisms known so far need food, and it is commonly believed all organisms unknown need it to. Size matters not - Eating is. Consumption continues ad infinitum.
Failure to eat all your spinach (and other healthy/unhealthy eats on your plate) leaves it to go bad eventually. Cosmonauts (atleast on ISS) consume irradiated food, or processed & packaged to last the duration of the mission. Left overs, if any, are promptly dispatched. In addition care is taken to maintain a sterile environment.
Yet http://cfpub.epa.gov/si/si_public_file_download.cfm?p_download_id=491399. writes to say
... Dust was collected over a period of several weeks in 2007 from HEPA filters in the U.S. Laboratory Module of the International Space Station (ISS). The dust was returned on the Space Shuttle Atlantis, mixed, sieved, and the DNA was extracted. Using a DNA-based method called mold specific quantitative PCR (MSQPCR), 39 molds were measured in the dust. ... Molds like Penicillium chrysogenum were measured on the Mir Space Station from the beginning of its on-orbit service
Even more recently http://en.rian.ru/world/20130618/181723912.html wrote to say
The Spaceflight101 portal said the delay was due to possible "mold and bacteria contamination on three cargo bags that are inside the spacecraft” and that a decision is yet to be made on whether the crew should use anti-mold kits to clean ATV-4 cargo before taking it inside the ISS.
- Where should I look to find mouldy food in ISS?
- Could mould even grow on crumb/fluid/gravy there in ISS habitat?
- Would mould be more susceptible to mutation in the combination of hard radiation, and microgravity?