Fleming, Lysozyme & Penicillin: The Discovery, and the Team That Made It a Medicine

The Lysozyme Rehearsal, 1921–22

Before penicillin, there was lysozyme — a discovery that deserves to be told in its own right, not simply as a footnote to the more famous story. In November 1921, while suffering from a cold, Fleming allowed a drop of his own nasal mucus to fall onto a culture plate seeded with a harmless yellow bacterium, Micrococcus lysodeikticus. A few days later he noticed that the bacteria immediately around the mucus had been dissolved away, leaving a clear zone. He had, by accident, found a natural antibacterial substance present in the body's own secretions: tears, saliva, mucus and egg white all contain it. He worked out with his colleague V.D. Allison that the active agent was an enzyme, which they published in 1922 as "lysozyme" — from the Greek for a substance that dissolves.

Lysozyme, on its own, is a modest discovery. It works chiefly against a narrow range of harmless environmental bacteria and against Gram-positive organisms with an exposed cell wall; it has almost no effect against the more dangerous Gram-negative bacteria and pathogens that cause serious human disease, and it never became an important therapeutic drug. Fleming himself understood its clinical limits.

Its real importance lies elsewhere, and this is the reason it belongs in the same story as penicillin rather than as a separate, minor curiosity. Lysozyme was Fleming's rehearsal. It taught him, in the most literal sense, what a zone of bacterial clearance around a substance looks like, and it trained him to ask, immediately and without embarrassment, what could have caused it. Seven years later, when a stray mould contaminated a Staphylococcus plate and produced exactly that kind of halo, Fleming recognised the pattern at once. Without the lysozyme years, there is a real possibility that the penicillin plate would simply have been washed and reused, as countless similar plates were by other bacteriologists before and since.

The 1928 Discovery

The famous moment came in Fleming's cramped, cluttered laboratory at St Mary's Hospital, Praed Street, London. In August 1928 he went on holiday to his country home at Barton Mills in Suffolk, leaving a stack of culture plates of Staphylococcus — the bacterium responsible for boils, sore throats and abscesses — piled in a corner of his bench. He returned on 3 September 1928, where his former assistant D.M. Pryce was waiting. Sorting through the plates, Fleming noticed that the lid had come off one, which had been contaminated by a blue-green mould. Around the mould was a clear "halo" in which the staphylococci had been dissolved away. "That's funny," he reportedly remarked.

He identified the contaminant as a Penicillium mould — originally classified as Penicillium notatum, and reclassified in 2011, through genome sequencing, as Penicillium rubens. Growing it in broth, he found the "mould juice" could kill many Gram-positive bacteria — staphylococcus, streptococcus, diphtheria — even when diluted hundreds of times, and on 7 March 1929 named the active substance "penicillin", to avoid, in his own words, "the repetition of the rather cumbersome phrase mould broth filtrate". He published his findings in the British Journal of Experimental Pathology in 1929, to almost total indifference from the medical world.

A note on dates, because this is where myths breed. Fleming's own famous recollection — of waking just after dawn on 28 September 1928 — has led many accounts to give that as the discovery date. The documentary evidence points instead to his return and first observation on 3 September 1928; the 28 September quotation appears to be a later, dramatised recollection of his moment of realisation. The Alexander Fleming Laboratory Museum at St Mary's itself dates the discovery to 3 September 1928.

Chance and the Prepared Mind

The episode is a near-perfect illustration of Pasteur's maxim that "chance favours the prepared mind". Fleming was characteristically honest about the role of luck: "Nature makes penicillin; I just found it," and "One sometimes finds what one is not looking for." But he was equally clear that luck alone explained nothing: "My only merit is that I did not neglect the observation." Countless bacteriologists had seen mould interfere with bacterial growth and simply discarded the plate; Fleming, primed first by a decade hunting for antibacterials and specifically by the lysozyme work seven years earlier, recognised what he was looking at.

The romantic image of a spore wafting through an open window onto the dish is almost certainly false. Fleming himself gave contradictory accounts over the years. His co-workers, including Pryce, later testified that his laboratory window was normally kept shut and was awkward to reach. The consensus today — supported by his former assistant Ronald Hare's detailed 1966 reconstruction — is that the spore most likely drifted up the stairwell from the mycology laboratory one floor below, run by the Irish mycologist C.J. La Touche, who was growing large collections of moulds for asthma research. Hare also showed that an unusual cold spell in London in late August and early September 1928 created exactly the temperature sequence needed for the mould to establish itself before the bacteria could overrun the plate — another, separate stroke of luck layered on top of the first.

How Penicillin Kills Bacteria

Penicillin works by attacking the one structure that many bacteria possess and human cells do not: the cell wall. Bacteria such as Staphylococcus are constantly building and rebuilding a rigid outer wall to contain their high internal pressure. Penicillin binds to the very enzymes — penicillin-binding proteins — that bacteria use to stitch that wall together. With the wall weakened, the bacterium's own internal pressure does the rest: the cell swells, ruptures and dies, and the body's immune system clears the debris.

Because human cells have no cell wall, the drug largely spares the patient. That is the secret of its exceptional safety, and the reason penicillin and its descendants — amoxicillin, methicillin, the cephalosporins, the carbapenems — remain workhorses of medicine almost a century after Fleming saw his halo.

From Mould Juice to Medicine

This is the section that this article treats as decisive, and where honesty matters more than national pride. Fleming discovered penicillin, but he did not — and by his own repeated admission, could not — turn it into a usable drug. "I am a bacteriologist, not a chemist," he said, and his attempts, with assistants Stuart Craddock and Frederick Ridley, to isolate and stabilise the fragile compound failed. By the early 1930s the chemical work had largely stalled, and Fleming's 1929 paper sat almost unread for a decade.

The breakthrough came ten years later and fifty miles away, at the Sir William Dunn School of Pathology at the University of Oxford. From 1939, a team led by the Australian pathologist Howard Florey and including the German-Jewish biochemist Ernst Chain — a refugee who had fled Nazi Germany in 1933 — took up Fleming's neglected paper. With Norman Heatley, Edward Abraham, Margaret Jennings and others, they devised methods to grow, extract and purify penicillin, proved it could cure infected mice in 1940, and worked out how to measure and concentrate it. Heatley in particular deserves to be named clearly and often: it was his improvised extraction apparatus — built, famously, from bedpans, milk churns, biscuit tins and bathtubs, because wartime Britain had no laboratory-grade equipment to spare — and his assay techniques that made purification at any usable scale possible at all. Florey and Chain provided the biological proof and chemical insight; Heatley provided the engineering that turned insight into deliverable quantities of drug.

The first human trial, in February 1941, is one of medicine's most poignant episodes. The patient was Albert Alexander, a 43-year-old Oxford-area policeman with a catastrophic infection of staphylococcus and streptococcus that had already cost him an eye and spread across his face and lungs. On 12 February 1941 he was given the precious penicillin and improved dramatically within days. But the Oxford team had so little of the drug that — even after recovering and recycling it from his urine — they ran out. Albert Alexander relapsed and died on 15 March 1941. His case proved penicillin worked in humans; it also proved that without industrial-scale production, the discovery was of no practical use whatsoever.

Wartime Britain could not build that production capacity, so in 1941 Florey and Heatley took penicillin to the United States. There, the crucial breakthroughs in scale came: at the USDA's Northern Regional Research Laboratory in Peoria, Illinois, scientists found that corn-steep liquor and deep-tank fermentation dramatically boosted yields, and a high-yielding mould strain was famously found on a mouldy cantaloupe in a Peoria market. By June 1944, American drug companies were producing vast quantities of penicillin — enough that the antibiotic went ashore with Allied troops on D-Day, sparing countless soldiers from fatal wound infections. The honest summary, stated as plainly as the insulin story on this site states Best's and Collip's contributions: Fleming lit the spark; Florey, Chain, Heatley and American wartime industry built the fire that actually warmed anyone.

Earlier Observations of Mould Antibiosis

Fairness requires one further correction to the popular story: Fleming was not the first person ever to notice that mould could interfere with bacterial growth.

• Ernest Duchesne, a French military doctor, documented the antibacterial effects of a Penicillium mould in a doctoral thesis in 1897, using it to treat infected guinea pigs. His thesis was accepted but essentially ignored, and he died in 1912 without ever influencing later events; the Institut Pasteur did not even acknowledge his work until decades afterward.
• John Tyndall, the Irish-born physicist, reported in 1875 that a Penicillium mould growing in a culture tube appeared to be inhibiting bacterial growth nearby, though he did not pursue the observation as a medical lead.
• Joseph Lister, the pioneer of antiseptic surgery, experimented with Penicillium glaucum against a human wound infection in the 1870s, with some apparent benefit, but did not publish a systematic account or follow the observation through.

None of these earlier sightings led to a named compound, a reproducible method, or a published route that other scientists could act upon. What made Fleming's 1928 observation different was not novelty of phenomenon but rigour of interpretation, naming and (eventual, if belated) publication — precisely the qualities his lysozyme apprenticeship had sharpened in him.

Nobel Prize and a Warning

Recognition, when it came, was immense. Fleming was elected a Fellow of the Royal Society in 1943 and knighted by King George VI in 1944. In 1945 the Nobel Prize in Physiology or Medicine was awarded jointly to Fleming, Florey and Chain "for the discovery of penicillin and its curative effect in various infectious diseases". Norman Heatley, whose apparatus and assays had made the Oxford team's chemistry usable at all, was not included; the Nobel statutes limit a shared prize to three names, and the historical judgement of many since has been that Heatley drew the short straw. Oxford itself later acknowledged the debt: in 1990 it awarded Heatley the first honorary doctorate of medicine in the university's 800-year history, a category previously reserved for people with a formal medical qualification.

It is Fleming's Nobel lecture, delivered on 11 December 1945, that now reads as almost eerily prophetic. He warned that misusing penicillin could breed resistant bacteria: "The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant." He concluded with a line that could be carved over every pharmacy door: "Moral: If you use penicillin, use enough." Eighty years on, with antimicrobial resistance recognised as one of the gravest threats to global health, that warning reads like a message sent forward from the future.

Myth vs Evidence

Legacy

The scale of the gift begun in that Paddington laboratory is hard to grasp. The New World Encyclopedia states that penicillin has saved at least 200 million lives since its first use as a medicine in 1942; Oxford's own Sir William Dunn School of Pathology puts the figure even higher, at over 500 million. Either way, it conquered once-deadly scourges including pneumonia, syphilis, gangrene, scarlet fever and meningitis, and made modern surgery, childbirth, cancer therapy and organ transplantation vastly safer.

Fleming died of a heart attack at his London home on 11 March 1955, and his ashes are buried in the crypt of St Paul's Cathedral — a rare honour. His old laboratory at St Mary's is preserved as the Alexander Fleming Laboratory Museum, reconstructed to its 1928 condition. He has never been forgotten in Scotland: in 2009 the Clydesdale Bank put his face on its £5 note, and his Nobel medal was acquired by National Museums Scotland in 1989 and is on public display. In Darvel, a memorial in Hastings Square — featuring a bust of Fleming and a circular flower bed inspired by the shape of a Petri dish — honours the town's most famous son, and his birthplace at Lochfield Farm is marked and still stands.

He was named one of Time magazine's 100 Most Important People of the 20th Century, one of the BBC's 100 Greatest Britons, and was voted the third "greatest Scot" in a 2009 STV poll, behind only Robert Burns and William Wallace. The grandest monument of all is abroad: a bronze bust by the Spanish sculptor Emilio Laiz Campos, with a full-length bronze matador saluting Fleming with his montera, was unveiled outside Madrid's Plaza de Toros de Las Ventas on 14 May 1964 — inscribed "To Dr Fleming with the gratitude of bullfighters", because penicillin had so reduced deaths from goring infections in the ring.

The deepest irony is the one Fleming himself foresaw. The man who gave the world its first antibiotic also gave it the first clear warning that the gift might be squandered — and the antimicrobial resistance crisis of today proves just how right the quiet Ayrshire farmer's son turned out to be.

Did You Know?

• Fleming's first antibacterial discovery, lysozyme, came from a drop of his own nasal mucus in 1921 — seven years before penicillin.
• The "dirty lab" was the key: had Fleming tidied his bench before his 1928 holiday, the contaminated plate would never have existed.
• An unusual cold spell in London in late summer 1928 let the mould and bacteria grow in exactly the sequence needed to form the halo.
• Fleming himself said, "I am a bacteriologist, not a chemist" — it took Oxford's Florey, Chain and Heatley to make penicillin a medicine.
• The first patient, Constable Albert Alexander, improved dramatically on penicillin in February 1941, then died in March when the tiny hand-made supply ran out.
• Norman Heatley built the extraction apparatus that scaled up penicillin from bedpans and milk churns — and was left off the 1945 Nobel Prize.
• D-Day ran partly on mould from a Peoria market: a high-yielding strain found on a mouldy cantaloupe helped American industry supply Normandy.
• The most famous Fleming statue is in Madrid, not Britain — unveiled in 1964 by grateful Spanish bullfighters.

Timeline

1. 6 Aug 1881

   Alexander Fleming born at Lochfield Farm, near Darvel, East Ayrshire

   Third of four children of farmer Hugh Fleming and his second wife Grace Stirling Morton

2. 1901–06

   Studies medicine at St Mary's Hospital Medical School, Paddington

   Qualifies with distinction in 1906; joins Sir Almroth Wright's research department, reputedly to stay on the rifle club

3. 1914–18

   Serves as a captain in the RAMC, wound-research laboratory, Boulogne

   Watches antiseptics fail against wound infection — the experience that sets his life's purpose

4. Nov 1921

   Discovers lysozyme from his own nasal mucus

   A plate of Micrococcus lysodeikticus is cleared in a ring around a drop of his nasal secretion

5. 1922

   Publishes lysozyme findings with V.D. Allison

   "On a remarkable bacteriolytic element found in tissues and secretions", Proc. Roy. Soc. B

6. 3 Sep 1928

   Returns from holiday to find a contaminated Staphylococcus plate

   A blue-green mould has cleared a halo of bacteria around itself

7. 7 Mar 1929

   Names the active substance "penicillin"

   Publishes in the British Journal of Experimental Pathology to almost total indifference

8. 1939–41

   Howard Florey, Ernst Chain and Norman Heatley, Oxford, purify and test penicillin

   Cure infected mice (1940); devise extraction and concentration methods that make human treatment possible

9. 12 Feb–15 Mar 1941

   Albert Alexander, Oxford policeman, becomes the first human patient

   Recovers dramatically, then dies when the tiny hand-made supply runs out

10. 1941–44

    Florey and Heatley take the project to the United States

    Peoria's Northern Regional Research Laboratory develops deep-tank fermentation and a high-yield mould strain

11. 6 Jun 1944

    Mass-produced American penicillin goes ashore with Allied troops on D-Day

    Wound infection deaths fall dramatically among Allied forces

12. 1944

    Fleming knighted by King George VI

    Elected FRS the previous year, 1943

13. 1945

    Fleming, Florey and Chain share the Nobel Prize in Physiology or Medicine

    Norman Heatley, whose engineering made scale-up possible, is not included

14. 11 Dec 1945

    Fleming's Nobel lecture warns of antibiotic resistance

    "Moral: If you use penicillin, use enough"

15. 11 Mar 1955

    Fleming dies in London, aged 73

    Ashes interred in the crypt of St Paul's Cathedral

16. 1990

    Oxford belatedly honours Norman Heatley

    Awarded the first honorary doctorate of medicine in the university's 800-year history, a doctorate previously reserved for medically qualified people

Notes on the Evidence

3 September or 28 September 1928? The Alexander Fleming Laboratory Museum and most documentary reconstructions date the discovery to Fleming's return on 3 September 1928. His own oft-quoted line about waking "just after dawn on September 28" is best read as a later, dramatised recollection of his moment of realisation, not a precise date of first observation.

Species name. The mould was originally identified as Penicillium notatum. Genome sequencing in 2011 reclassified the actual strain used by Fleming, Florey and Chain as Penicillium rubens, a distinct but closely related species.

Lives saved figures vary widely — from roughly 200 million (New World Encyclopedia) to over 500 million (Oxford's Sir William Dunn School of Pathology) — because sources differ on start dates, whether to include penicillin's chemical descendants, and methodology. Both figures are presented above with their sources rather than being averaged into a single false-precision number.

Heatley's exclusion. The Nobel Prize in Physiology or Medicine can be shared by at most three people under the Nobel Foundation's statutes, which structurally excluded a fourth contributor no matter how essential. This is the same statutory limit, and broadly the same pattern of an essential technical contributor being left off a prize later partly corrected by other honours, seen in the University of Toronto's insulin story with Charles Best.

Earlier mould observations. Duchesne's 1897 thesis is well documented but had no causal influence on Fleming, who almost certainly worked independently and in ignorance of it. We therefore credit Duchesne, Tyndall and Lister as earlier observers of a related phenomenon, without suggesting Fleming's work was derivative of theirs.