... Penicillin is mould. Mould has been known for centuries to have special properties that resist infection, but no scientific evidence to back it up. The ba

... Penicillin is mould. Mould has been known for centuries to have special properties that resist infection, but no scientific evidence to back it up. The bacteria culture was accidentally left open during a vacation and some mold started growing on it. When they returned, it had killed off the bacteria. Fleming isolated the mould (penicillin) and had a provable antibiotic. Lab errors still happen, though, because they are still run by humans.