In Sep. 1928, Fleming witnessed the contamination of one
of his Staphylococcus plates by Penicillium rubrum and observed
a halo of inhibition on his bacterial colonies (Fleming 1929).
The antibiotic effect from this mould was via the production of
the secondary metabolite penicillin, which was later refined
for production by Ernst Chain and Howard Florey (Henk et al.
2011). These three scientists were acknowledged for their
discovery by joint award of the Nobel Prize for Physiology or
Medicine in 1945.
The taxonomy and true identity of Fleming’s fungus was
initially and has remained persistently controversial. The
original penicillin-producing fungus was first described as
Penicillium rubum by the experienced mycologist Charles La