In simple terms
The discovery of penicillin in 1928 revealed the first widely effective antibiotic, a substance that could kill disease-causing bacteria inside the body, and it began the modern era of treating bacterial infections with medicine. [2]
How it was discovered
Scottish bacteriologist Alexander Fleming returned from a summer holiday in 1928 to find that one of his bacterial culture plates, left uncovered, had become contaminated with a mold. Looking closer, he noticed something unusual: the bacteria growing near the mold had been killed, while bacteria farther away were unaffected. [1] He identified the mold as a strain of Penicillium and correctly concluded it was producing a substance that killed the surrounding bacteria, which he named penicillin.
Fleming published his findings, but producing enough stable, purified penicillin to use as an actual medicine proved extremely difficult, and his discovery attracted only limited attention for over a decade. It was not until the late 1930s and early 1940s that Howard Florey and Ernst Chain, working at Oxford University, developed methods to extract, purify, and mass-produce penicillin reliably. [2]
Why it matters
Penicillin became widely available during World War II, dramatically cutting deaths from infected wounds and diseases like pneumonia among soldiers and civilians alike, and it opened the door to the modern antibiotic era. [1] Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology or Medicine for the discovery and development of penicillin.
Where you’ll see it
- Common antibiotic medications still derived from or related to penicillin
- Medical history exhibits and public health education
- Ongoing research into antibiotic resistance, a direct consequence of antibiotics’ success
- Hospital infection treatment protocols worldwide
Example
During World War II, mass production of penicillin meant that infected battlefield wounds, which had often been fatal in earlier wars, could increasingly be treated successfully with antibiotics.
Often confused with
Antibiotics as a category include many substances beyond penicillin, developed later from different molds, bacteria, or synthetic processes; penicillin was specifically the first of these widely used antibiotics to be discovered and developed for medical use.
Key facts
- Alexander Fleming discovered penicillin's antibacterial effect in 1928 after noticing that a mold contaminating one of his bacterial culture plates had killed the surrounding bacteria.1
- The mold was identified as a strain of Penicillium, giving the substance its name.1
- Fleming's initial findings attracted limited attention, and it took over a decade before Howard Florey and Ernst Chain developed methods to produce and purify penicillin in large enough quantities for medical use.2
- Penicillin became widely available during World War II, dramatically reducing deaths from infected wounds among soldiers.2
Quick checkWhy wasn't penicillin used as a medicine for over a decade after Fleming's initial 1928 discovery?Show answer
No one had yet worked out how to produce and purify it in large, stable, reliable quantities; it took Howard Florey and Ernst Chain's later research to develop those methods before it could be used widely as a medicine.
Sources
- National WWII Museum. How Penicillin Became the Wonder Drug of WWII. Undated (accessed 1 November 2026)
- Nobel Prize. Alexander Fleming - Biographical. Undated (accessed 1 November 2026)
Editorially reviewed by Last reviewed November 1, 2026Researched and drafted with AI assistanceReport an issue