This is a thing I’ve seen an awful lot lately in novels that are set in pre-industrial historical times, or in medieval fantasy type books. Most recently I came across it in Bernard Cornwell’s “Vagabond”. Modern authors seem to like to have their characters include “moldy bread” as an ingredient in their poultice or other folky healing concoction. The point is obviously to make us modern readers think, “Ah ha! Little do those characters know that some kinds of bread mold make penicillin! What clever little pre-industrial folk healers they are, and how clever I am to have spotted that!”
But is there any evidence that people ever actually used to do this in the days before penicillin was discovered, or is it all just a cheap anachronistic ploy?
I have similarly heard the rumors of lab notes for a medical student from decades before the discovery/invention of penicillin, in which he took note that the instructor had said to make sure a certain type of bread mold didn’t get into their petri dishes because it’d kill off everything in the dish and ruin their experiments, and have wondered if there were any truth to this.
This page says that ancient Egyptians used moldy bread to treat infections. And it also mentions (as Ethilrist says) a mold contaminating petri dishes and killing off everything else, leading to the discovery of penicillin.
Somewhat surpringly, this wikipedia page on the History of Penicillinbacks it up as well, although it’s relying on one cite to another webpage whcih doesn’t cite its sources.
I’ve spent a few minutes trying to track down the ‘John Parkington’ referred to as writing about using moulds to treat infections back in 1640 but can only seem to find variations on the wording in wikipedia, which makes me suspicious.
Just to make things even murkier - the exact table and wording from wikipedia appears in this 2012 Microbiology textbook again without any obvious citation.
From what I understand, there were a few books of medicine in the Olden Days which suggested moldy bread, but they also suggested a wide variety of other things that were definitely harmful, and a poultice of moldy bread isn’t likely to do any good anyway.