Apparently molds which make penicillin are not difficult to grow from rotting food. http://io9.com/in-case-of-apocalypse-heres-how-to-make-penicillin-in-1110902296 Was there any historical pre-scientific societies that used moldy food as a cure for infection?
If you don't get an answer here, you might try /r/historyofmedicine. Just be warned that it is a time sink!