By: History.com Editors

1928

Penicillin discovered by Sir Alexander Fleming

History.com Editors

Published: February 09, 2010

Last Updated: January 24, 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.

Timeline

Also on This Day in History

Discover more of the major events, famous births, notable deaths and everything else history-making that happened on September 3rd

1777

The Stars and Stripes flies in battle for the first time

The American flag is said to have flown in battle for the first time, during a Revolutionary War skirmish at Cooch’s Bridge, Delaware. Patriot General William Maxwell ordered the stars and stripes banner raised as a detachment of his infantry and cavalry met an advance guard of British and Hessian troops. The rebels were defeated and forced to retreat to General George Washington’s main force near Brandywine Creek in Pennsylvania.

1783

Treaty of Paris signed

The American Revolution officially comes to an end when representatives of the United States, Great Britain, Spain and France sign the Treaty of Paris on September 3, 1783. The signing signified America’s status as a free nation, as Britain formally recognized the independence of its 13 former American colonies, and the boundaries of the new republic were agreed upon: Florida north to the Great Lakes and the Atlantic coast west to the Mississippi River.

Representatives Signing 1783 Treaty Of Paris

1914

Pope Benedict XV named to papacy

On September 3, 1914, barely a month after the outbreak of World War I, Giacomo della Chiesa is elected to the papacy of the Roman Catholic Church, becoming Pope Benedict XV.

1919

Wilson embarks on tour to promote League of Nations

On September 3, 1919, President Woodrow Wilson embarks on a tour across the United States to promote American membership in the League of Nations, an international body that he hoped would help to solve international conflicts and prevent another bloody world war like the one from which the country had just emerged—World War I. The tour took an enormous toll on Wilson’s health.

1939

Britain and France declare war on Germany

On September 3, 1939, in response to Hitler’s invasion of Poland, Britain and France, both allies of the overrun nation declare war on Germany.

1943

Allies invade Italian mainland

The British 8th Army under Field Marshal Bernard L. Montgomery begins the Allied invasion of the Italian peninsula, crossing the Strait of Messina from Sicily and landing at Calabria—the “toe” of Italy. On the day of the landing, the Italian government secretly agreed to the Allies’ terms for surrender, but no public announcement was made until September 8.

2004

Russian school siege ends in bloodbath

A three-day hostage crisis at a Russian school comes to a violent conclusion after a gun battle erupts between the hostage-takers and Russian security forces. In the end, over 300 people died, many of them children, while hundreds more were injured.

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Citation Information

Article title
Penicillin discovered by Sir Alexander Fleming
Website Name
History
Date Accessed
March 23, 2025
Publisher
A&E Television Networks
Last Updated
January 24, 2025
Original Published Date
February 09, 2010

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