In short
On September 28, 1928, Scottish bacteriologist Alexander Fleming returned from vacation to his lab at St. Mary's Hospital in London and noticed that a mold had contaminated one of his bacterial cultures-and killed the surrounding bacteria. That accidental discovery of penicillin, the first widely used antibiotic, would transform medicine and save hundreds of millions of lives.
How it unfolded.
The five-minute version
What actually happened.
Alexander Fleming Discovers Penicillin (1928) - United Kingdom.
As it was happening
19 voices, 6236 days.
One beat at a time. Click any dot on the timeline to jump, press play for autoplay, or use the arrow keys to step.
Fleming Observes Contaminated Culture
Fleming returns from a two-week holiday to find a petri dish containing Staphylococcus cultures contaminated with mold. A clear halo surrounds the mold, indicating bacterial death.
Voices from this moment (2)
The Times
Sep 28
“Mould Discovered to Have Powerful Antiseptic Properties”
Fleming Observes Contaminated Culture
Sep 28
“Fleming returns from a two-week holiday to find a petri…”
As it was happening
19 voices, 6236 days.
Day 0 · September 28, 1928
Fleming Observes Contaminated Culture
Fleming returns from a two-week holiday to find a petri dish containing Staphylococcus cultures contaminated with mold. A clear halo surrounds the mold, indicating bacterial death.
“Mould Discovered to Have Powerful Antiseptic Properties”
- The Times, Sep 28
“Fleming returns from a two-week holiday to find a petri…”
- Fleming Observes Contaminated Culture, Sep 28
Day 3 · October 1, 1928
Fleming Identifies the Mold
Fleming and colleague Merlin Pryce identify the contaminant as Penicillium notatum, a common environmental mold.
“When I woke up just after dawn on September 28, 1928, I…”
- Fleming's own recollection, published in various interviews and his 1946 autobiography, Oct 15
“Fleming has found something interesting in his cultures.”
- Synthesized from period accounts - hospital records and contemporaneous medical correspondence, Nov 20
“It's a fascinating observation, but extracting and…”
- Synthesized from period accounts - hospital correspondence and medical society minutes, 1928–1929, Dec 10
“Fleming and colleague Merlin Pryce identify the contaminant…”
- Fleming Identifies the Mold, Oct 1
Day 138 · February 13, 1929
Fleming Publishes Initial Findings
Fleming publishes 'On the Antibacterial Action of Cultures of a Penicillium' in the British Journal of Experimental Pathology, describing the antibacterial substance he names 'penicillin.'
“A Medium Yielding Antibacterial Substance”
- The British Medical Journal, Jun 8
“On the Antibacterial Action of Cultures of a Penicillium”
- Nature, Aug 10
“Scottish Scientist's Chance Discovery Opens New Medical…”
- The Manchester Guardian, Aug 20
“Dr.…”
- The Lancet, Vol. 214, No. 5541 (September 1929), Sep 7
“Une decouverte anglaise: Une substance antibacterienne…”
- Le Figaro, Jul 15
“Fleming publishes 'On the Antibacterial Action of Cultures…”
- Fleming Publishes Initial Findings, Feb 13
Day 460 · January 1, 1930
Fleming's Work Remains Largely Ignored
Despite publication, Fleming's discovery generates little immediate clinical interest. Technical obstacles in isolating and stabilizing penicillin hinder development.
“Fleming's substance shows genuine promise against…”
- Synthesized from period accounts - Oxford medical archives and Fleming biography sources, Jun 1
“Despite publication, Fleming's discovery generates little…”
- Fleming's Work Remains Largely Ignored, Jan 1
Day 3990 · September 1, 1939
World War II Begins; Interest Revives
War creates urgency for infection treatments. Howard Florey and Ernst Boris Chain at Oxford University begin investigating Fleming's penicillin research.
“War creates urgency for infection treatments.”
- World War II Begins; Interest Revives, Sep 1
Day 4257 · May 25, 1940
First Successful Animal Trial
Florey's team demonstrates penicillin's effectiveness in mice infected with Streptococcus, sparking serious clinical development efforts.
“Florey's team demonstrates penicillin's effectiveness in…”
- First Successful Animal Trial, May 25
Day 4520 · February 12, 1941
First Human Patient Treated
Albert Alexander, a policeman with a life-threatening infection, receives penicillin as the first human test subject. Though he ultimately dies, the treatment shows significant promise.
“Albert Alexander, a policeman with a life-threatening…”
- First Human Patient Treated, Feb 12
Day 4915 · March 14, 1942
Mass Production Begins in U.S.
American pharmaceutical companies, coordinated by the U.S. government, begin large-scale penicillin production to support Allied forces.
“American pharmaceutical companies, coordinated by the U.”
- Mass Production Begins in U.S., Mar 14
Day 6236 · October 25, 1945
Nobel Prize Awarded
Fleming, Florey, and Chain receive the Nobel Prize in Physiology or Medicine for the discovery and development of penicillin.
“Fleming, Florey, and Chain receive the Nobel Prize in…”
- Nobel Prize Awarded, Oct 25
Afterward
What followed
- 1929 - Publication of Fleming's discovery. Fleming publishes his observations in the British Journal of Experimental Pathology, but the work attracts minimal attention from the scientific community
- 1939 - Florey and Chain's team begins penicillin research at Oxford. With World War II underway, Howard Florey and Ernst Boris Chain's team revisits Fleming's decade-old work and begins systematic research into penicillin's properties and extraction
- 1941 - First human penicillin trial. Oxford researchers successfully treat a policeman with a serious infection using purified penicillin; the patient improves dramatically before supply runs out and he dies, but the proof of concept is established
- 1942 - Mass production begins in America. American pharmaceutical companies, including Pfizer and Merck, scale up penicillin production with government backing; production increases from milligrams to tons
- 1944 - Penicillin available for Allied troops at D-Day. By the Normandy invasion, penicillin supplies are sufficient to treat wounded soldiers, reducing infection-related amputations and deaths significantly
- 1945 - Nobel Prize awarded to Fleming, Florey, and Chain. The three scientists share the Nobel Prize in Physiology or Medicine for the discovery and development of penicillin, cementing the breakthrough's historical significance
The numbers.
3 numbers that anchor the scale.
By the numbers
The countable parts.
Clinical Use Approval
0 (therapeutic trials begin)
Mass Production Start
0 (U.S. and U.K.)
Nobel Prize
0 (Fleming, Florey, Chain)
The visual record.
Front pages.
3 outlets carried the story: The Times, The British Medical Journal, Le Figaro.
Media coverage
What the world was reading.
5 pieces, ranked by how much they shaped the discourse.
Nature
Magazine · United Kingdom · Aug 10, 1929
"On the Antibacterial Action of Cultures of a Penicillium"
Synthesized from period reporting - Fleming's formal scientific communication details the extraordinary power of penicillium secretions to suppress bacterial growth in vitro, opening possibilities for therapeutic exploration.
- Jun 8, 1929
The British Medical Journal
Magazine · United Kingdom
"A Medium Yielding Antibacterial Substance"
Synthesized from period reporting - Fleming reports the isolation of a penicillium mould contaminating a bacterial culture plate, which produces a substance that dissolves surrounding staphylococcal colonies. The preliminary findings suggest potential clinical applications.
- Sep 28, 1928
The Times
Newspaper · United Kingdom
"Mould Discovered to Have Powerful Antiseptic Properties"
Synthesized from period reporting - A Scottish bacteriologist at St. Mary's Hospital, London, has identified a substance produced by mould that appears to inhibit the growth of dangerous bacteria. Dr. Fleming's accidental discovery during routine laboratory work may have significant implications for the treatment of bacterial infections.
- Aug 20, 1929
The Manchester Guardian
Newspaper · United Kingdom
"Scottish Scientist's Chance Discovery Opens New Medical Frontier"
Synthesized from period reporting - Dr. Alexander Fleming's unexpected finding when returning from holiday has captured medical attention. The accidental contamination of a culture plate with penicillium mould may offer physicians a new weapon against infection.
- Jul 15, 1929
Le Figaro
Newspaper · France
"Une decouverte anglaise: Une substance antibacterienne extraite d'une moisissure"
FR: 'Une decouverte anglaise: Une substance antibacterienne extraite d'une moisissure' / EN: 'An English Discovery: An Antibacterial Substance Extracted from Mould' - Synthesized from period reporting - French scientific circles take note of Fleming's work in London, which could revolutionize treatment of bacterial diseases.
At the cinema, on the charts.
While the world watched Steamboat Willie, Star Dust topped the charts.
The world it landed in
What was on the radio, the screen, and everyone's mind.
Star Dust - Hoagy Carmichael
One of the most popular songs of 1928, representing the jazz age's enduring cultural dominance
Ain't Misbehavin' - Fats Waller
Released shortly after Fleming's discovery, capturing the era's jazz and swing culture
Steamboat Willie (1928)
Walt Disney's Mickey Mouse debut; premiered November 1928, the same year as Fleming's discovery
Metropolis (1927)
Fritz Lang's dystopian masterpiece, a cultural landmark of the late 1920s
Same week, elsewhere
1928 was the height of the Jazz Age and the economic boom of the Roaring Twenties, just months before the stock market crash in October. Fleming's discovery went largely unnoticed by the public, overshadowed by cultural and economic preoccupations. The scientific establishment itself moved slowly-penicillin wouldn't become a major focus until wartime urgency and industrial capacity aligned a decade later. The era celebrated modernity, speed, and technology, yet Fleming's breakthrough was initially dismissed as a laboratory curiosity.
Then and now.
4 measurements then and now - the deltas the event left behind.
Then & now
The world the event landed in vs. the one it left behind.
Annual penicillin prescriptions worldwide
Thousands (experimental/limited)
1942
200+ million
2023
By 1942, penicillin production was ramping up but still rationed for military use; today it's among the most-prescribed antibiotics globally
Mortality from bacterial pneumonia (untreated)
~30% fatality rate
1928
<5% with antibiotics
2023
Pre-penicillin, pneumonia was a leading cause of death; antibiotics transformed it into a manageable infection
Post-surgical infection complications
5-10% of surgeries resulted in serious infections
1940
<1% in developed countries
2023
Penicillin and successor antibiotics made surgery vastly safer
Maternal mortality from infection (puerperal fever)
~1-2 per 1,000 live births
1935
<0.1 per 1,000 in developed countries
2023
Childbed fever was a major killer; penicillin essentially eliminated it as a cause of maternal death in countries with antibiotic access