Alexander Fleming’s penicillin discovery ushers in the age of antibiotics

Story: 1928 C.E.  |  Last updated: September 28, 1928

On the morning of September 28, 1928 C.E., a Scottish bacteriologist returned to his cluttered lab at St. Mary’s Hospital in London after a summer holiday and noticed something strange growing on a petri dish — something that would, within two decades, save millions of lives and permanently alter the practice of medicine.

Key findings

• Penicillin discovery: Alexander Fleming observed that a mold, Penicillium notatum, had contaminated a petri dish seeded with Staphylococcus aureus — and that a clear zone around the mold showed the bacteria could not grow there.
• Mold contamination: Rather than discarding the ruined culture, Fleming studied it carefully, ultimately concluding that the mold produced a substance capable of killing or halting the growth of dangerous bacteria.
• Antibiotic research: Fleming published his findings in 1929 C.E., but it would take a team of Oxford scientists — Howard Florey, Ernst Chain, and Norman Heatley — to isolate, purify, and mass-produce the drug that Fleming’s observation had pointed toward.

What Fleming actually found

The discovery was partly luck and partly trained instinct. Many scientists before Fleming had noticed bacterial cultures going wrong. Fleming was among the few who stopped to ask why.

The mold that had drifted onto his petri dish was Penicillium notatum. Under the microscope, Fleming could see that wherever the mold had taken hold, the surrounding staphylococcal colonies had dissolved. He spent the following weeks growing more of the mold, confirming that it consistently produced this bacteria-killing effect. He called the active substance “penicillin.”

What Fleming could not do — and openly acknowledged — was take the next steps. He lacked the chemistry background and laboratory resources to isolate penicillin, purify it, and figure out how to use it in people. That work waited nearly a decade.

The Oxford team that made it medicine

In 1938 C.E., Howard Florey, director of the Sir William Dunn School of Pathology at Oxford, came across Fleming’s published paper while reviewing back issues of a scientific journal. He recognized what it might mean and assembled a team to pursue it.

Ernst Chain, a Jewish German biochemist who had fled Nazi Germany, became one of Florey’s most important collaborators. Together with Norman Heatley — who improvised production methods using every available bottle, flask, and hospital bedpan — they produced crude extracts of penicillin and began testing them on animals. In summer 1940 C.E., 25 mice infected with lethal streptococcus received penicillin injections. They survived. The 25 that received nothing died.

The first human trial, on an Oxford police constable named Albert Alexander in 1940 C.E., was both promising and heartbreaking. Alexander had developed a life-threatening infection from a rose thorn scratch. Penicillin began to turn it around — but Florey and Chain ran out of the drug before the infection was fully cleared, and Alexander died. The lesson was stark: the drug worked, but producing enough of it was a crisis in its own right.

Mass production and the war that proved everything

In 1941 C.E., Florey and Heatley flew to the United States to work with American scientists in Peoria, Illinois, on scaling up production. A key breakthrough came by accident: a laboratory assistant named Mary Hunt brought in a cantaloupe from a local market that was covered in a golden mold. That mold turned out to be Penicillium chrysogenum, which produced 200 times more penicillin than Fleming’s original strain. Enhanced further with X-ray mutation techniques, it ultimately yielded 1,000 times as much.

The timing proved critical. Throughout history, infection — not battle wounds — had been the leading killer of soldiers. In World War I, the death rate from bacterial pneumonia among troops reached 18 percent. In World War II, with penicillin increasingly available, it fell to less than 1 percent. By the war’s end, American pharmaceutical companies were producing 650 billion units of penicillin per month.

In March 1942 C.E., Anne Miller became the first civilian successfully treated with the drug — she had been near death from a bloodstream infection after a miscarriage. Her recovery was described by attending physicians as miraculous.

Lasting impact

The penicillin discovery did not just cure infections. It created an entirely new field of medicine. The concept that a naturally occurring biological compound could be harnessed as a targeted weapon against bacteria opened the door to streptomycin, tetracycline, erythromycin, and hundreds of other antibiotics developed in the following decades.

Surgical procedures that had carried enormous infection risks became routine. Childhood bacterial illnesses that had been near-certain death sentences — scarlet fever, bacterial meningitis, rheumatic fever — became treatable. The World Health Organization estimates that antibiotics have contributed to a dramatic increase in global life expectancy over the 20th century, with infections that once killed within days now cleared in a course of pills.

Fleming, Florey, and Chain shared the Nobel Prize in Physiology or Medicine in 1945 C.E. Fleming used his acceptance speech to warn — with striking foresight — that overuse of penicillin could lead to bacterial resistance. Heatley, whose improvised production methods were arguably as important as the science itself, was not included in the Nobel. Oxford partially corrected that in 1990 C.E. by awarding him its first ever honorary doctorate of medicine in the university’s 800-year history.

Blindspots and limits

Fleming’s warning about resistance turned out to be one of the most important unheeded cautions in medical history. The U.S. Centers for Disease Control and Prevention now estimates that antibiotic-resistant bacteria cause at least 1.27 million deaths globally each year — a crisis that grows directly from the overuse and misuse that Fleming foresaw. The credit history of penicillin’s development also remains skewed: Heatley’s contributions to mass production are still far less widely known than Fleming’s famous petri dish, and the labor of unnamed technicians, procurement workers, and wartime factory workers who scaled production has gone largely unrecorded.

Read more

For more on this story, see: PBS NewsHour — The real story behind the world’s first antibiotic

For more from Good News for Humankind, see:

• A drug cuts Alzheimer’s risk in half in a landmark prevention trial
• U.K. cancer death rates fall to their lowest level on record
• The Good News for Humankind archive on global health

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