What is the current scientific name of Fleming's original penicillin-producing mould?

The current scientific name of Fleming’s original penicillin-producing mould is Penicillium rubens.

Fleming discovered the mould in 1928 after it contaminated a culture of Staphylococcus bacteria at St Mary’s Hospital in London. The mould inhibited bacterial growth, leading him to investigate and name its antibacterial substance penicillin. Its identity, however, changed several times as mycologists compared it with related Penicillium species.

C. J. La Touche initially identified the specimen as Penicillium rubrum. Charles Thom later associated it with P. notatum and the P. chrysogenum group, and P. chrysogenum became the commonly used name for many years. This history explains why older books and quiz sources may give a different answer.

Genomic sequencing and phylogenetic analysis published in 2011 resolved the modern classification: Fleming’s original strain belongs to P. rubens. It should not be confused with P. digitatum, P. expansum or P. roqueforti, which are different mould species.