Rachel,
 
Since it is a microbiology laboratory, have you considered any of the bio logical organisms that contribute to the problem of "Athlete's foot" (some are odoriferous fungi) that might be being grown/incubated?  Could t here be some cultures of such in there?  Certainly, many "moldy" o dors are actually from biological organisms.  Could it in fact be th at "dirty socks" are actually dirty socks (as in someone's overlooked gym b ag)?
 
I'm reminded of a case at a major IBM facility a friend of mine investigate d some years ago of "sick building syndrome" in an office area that turned out to be a "lost" mouldy orange buried beneath paperwork in a worker's low er desk drawer (after an expensive IH evaluation of multiple worker odor co mplaints had already been done). 
 
Just a thought.
 
Alan
Alan H. Hall, M.D.
Medical Toxicologist.