Original Penicillin Mold Revived

Freeze-dried sample of the Penicillium mold Source: CABI

The 92-year-old mold that led to the discovery of penicillin brought back from the dead in the hopes to fight superbugs.

Alexander Fleming’s accidental discovery of Penicillin revolutionized the treatment of bacterial infections in the 1920s. A team of scientists has now sequenced the original penicillium mold in the hopes to fight antibiotic resistance.

Antibiotic resistance is one of the biggest threats to global health today. Resistant bacteria account for over 750,000 deaths per year.

The Accidental Penicillin

In 1928, Alexander Fleming was working as a researcher at St. Mary’s Hospital in London. At the time, he was experimenting with Staphylococcus Aureus bacteria. Before leaving for his vacation, Alexander had left three staphylococcus culture plates on his bench. 

On his return, he found one of the Petri dishes had developed a strange blue-green mold. The fungus, Penicillium notatum, destroyed the bacterial colonies immediately surrounding it and spared those further away.

He then isolated the penicillin from the mold. 

Fleming discovered the fungus was capable of killing a wide range of bacteria including those that cause scarlet fever, meningitis, and gonorrhea. Later on, in the 1940s, scientists were able to purify penicillin into a stable and effective form. 

A sample of the original penicillium mold has stayed frozen since 1945. The sample has been regrown multiple times over the years.

We realized, to our surprise, that no one had sequenced the genome of this original Penicillium, despite its historical significance to the field

Professor Tim Barraclough (study author)
This mold was regrown from Alexander Fleming’s frozen sample that produced the first antibiotic, penicillin.
Source: CABI

Genome Sequencing Performed on the Original Mold

The team of researchers from Imperial College London and, Oxford University extracted DNA from the cryopreserved sample for genome sequencing.

The original strain was compared to two commercial strains from the United States. These strains were compared for changes in genomic structure and variation in genes.

Specifically, the genes responsible for regulating penicillin production and producing penicillin were studied in detail.

The findings of the study were published in the journal Scientific Reports. 

It might give us some suggestions for how we could try and improve our use or the design of antibiotics for combating bacteria

Professor Tim Barraclough (study author)

What Did the Study Reveal?

Although the genetic code between the original and US strain was similar, the US strain had more copies of genes that regulate penicillin production. The enzymes responsible for producing penicillin were also different among the strains.

Thus, suggesting the mold underwent evolutionary changes in order to survive against encountered bacteria. 

In conclusion, researchers hope studying the differences between the US and UK strains can help improve future penicillin production and deal with the rising antibiotic resistance.


Pathak, A., Nowell, R.W., Wilson, C.G. et al. Comparative genomics of Alexander Fleming’s original Penicillium isolate (IMI 15378) reveals sequence divergence of penicillin synthesis genes. Sci Rep 10, 15705 (2020). https://doi.org/10.1038/s41598-020-72584-5


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