By: HISTORY.com Editors

1928

Penicillin discovered by Sir Alexander Fleming

Universal Images Group via Getty
Published: February 09, 2010Last Updated: September 15, 2025

Sir Alexander Fleming was a young bacteriologist when an accidental discovery led to one of the great developments of modern medicine on September 3, 1928. Having left a plate of Staphylococcus bacteria uncovered, Fleming noticed that a mold that had fallen on the culture had killed many of the bacteria. He identified the mold as Penicillium notatum, similar to the kind found on bread.

In 1929, Fleming introduced his mold by-product called penicillin to cure bacterial infections.

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Citation Information

Article Title
Penicillin discovered by Sir Alexander Fleming
Website Name
History
Date Accessed
April 22, 2026
Publisher
A&E Television Networks
Last Updated
September 15, 2025
Original Published Date
February 09, 2010