Timeline Entry
In 1928, at St Mary's Hospital in London, bacteriologist Alexander Fleming investigated a contaminating mould that inhibited staphylococci on a culture plate. He named the antibacterial filtrate “penicillin” and published its selective effects in June 1929. The observation was important, but it was not yet a stable compound, a tested systemic treatment, or a manufactured medicine (Fleming 1929).
This entry follows the event from a London laboratory observation through Oxford experiments in 1939–41 and Anglo-American wartime production in 1941–45. Penicillin changed medicine only when biochemical, clinical, technical, industrial, and state work converted a fragile mould product into a drug—and that process also exposed limits of evidence, unequal access, and bacterial resistance.
Historical Significance
Fleming established that a product of a Penicillium mould could inhibit some bacteria without obviously damaging the animal tissues he tested. Oxford researchers later produced concentrated material, measured its activity, studied it in infected animals, and administered it to severely ill patients. Those were different evidential steps, not one instantaneous discovery (Chain et al. 1940; Abraham et al. 1941).
A medicine that could not be purified, assayed, stored, or replenished could not reliably treat infection. Ceramic culture vessels at Oxford, new growth media and mould strains at Peoria, and industrial deep-tank fermentation were therefore medical achievements as well as engineering ones. Government coordination and unusually open exchange among rival firms helped join them together (Quinn 2013).
Penicillin acted against a range of susceptible bacteria, not every infection. Resistance was observed before mass use, and scarce wartime supplies were rationed. Postwar abundance then encouraged the prescribing, promotion, and reform debates that became part of the antibiotic era (Abraham and Chain 1940; Podolsky 2015).
Therapeutic Context
Late nineteenth- and early twentieth-century bacteriology made many pathogenic organisms visible and distinguishable, but diagnosis did not automatically provide a safe drug. Surgery, drainage, antisepsis, supportive care, vaccines, and type-specific antiserum could help in particular circumstances. Paul Ehrlich and Sahachiro Hata's arsenical compound Salvarsan entered treatment for syphilis in 1910, and the sulphonamides transformed treatment of several bacterial infections from the mid-1930s. Penicillin did not arrive in a therapeutic vacuum (see Salvarsan introduced; Greenwood 2008).
Those earlier therapies also had boundaries. Antisera depended on matching an infecting type and on rapid organisation; arsenical compounds could be toxic; and sulphonamides did not work against all organisms or in all sites of infection. The historical novelty of penicillin was therefore not that physicians had never tried antimicrobial treatment. It was the combination of strong activity against certain common pathogens, comparatively low toxicity in early studies, and eventual manufacture at a scale that made repeated dosing possible (Weiser 2006).
Period authors called such treatment “chemotherapy”: the use of a chemical agent within the body to act selectively on a disease-causing organism. In this historical setting the word is broader than its now familiar association with cancer treatment.
The 1928–29 Evidence
Fleming was studying variants of staphylococci when a mould contaminated one plate. Colonies near it had become transparent or failed to develop normally. Subculturing the mould and testing filtered broth allowed him to move beyond a single dish: activity was marked against staphylococci, streptococci, and some other organisms, while members of what he called the “coli-typhoid group” were not inhibited. The effect was selective from the beginning (Fleming 1929).
In the 1929 paper the name referred to antibacterial material in mould culture filtrate. Fleming reported that its activity declined in storage and emphasised its value in suppressing unwanted bacteria while isolating B. influenzæ—the period name for Haemophilus influenzae. Fleming and his assistants Stuart Craddock and Frederick Ridley attempted to concentrate the material but did not obtain a stable purified medicine. Fleming briefly suggested possible use on susceptible infections, especially by local application, but published no evidence of systemic cure in patients.
The familiar holiday, open-window, and single “eureka” narrative was assembled from later recollections. Ronald Hare used surviving notebooks, testimony, and experimental reconstruction to question parts of that sequence. The contemporary paper securely establishes the culture observation and experiments; it does not establish an exact day or every detail later attached to the plate (Hare 1982).
The difference matters because “accidental” can mislead in two directions. Contamination was accidental, but recognising an anomaly, culturing the mould, comparing organisms, naming the material, and publishing were acts of investigation. Conversely, those acts did not solve purification, dosage, toxicity, clinical effectiveness, or manufacture. The related culture-plate source profile examines what the preserved object and its later replicas can—and cannot—show.
Oxford, 1939–41
At the Sir William Dunn School of Pathology, Howard Florey and Ernst Chain placed penicillin within a wider programme on antibacterial substances. Norman Heatley devised a sensitive cylinder-plate assay and practical extraction equipment; Edward Abraham worked on purification; Margaret Jennings and Florey investigated biological effects; A. D. Gardner studied bacteriology. Measurement was essential because the preparation varied from batch to batch and lost activity during processing (Dunn School of Pathology).
On 24 August 1940, Chain, Florey, Gardner, Heatley, Jennings, Jean Orr-Ewing, and Arthur Sanders reported that penicillin protected mice experimentally infected with otherwise lethal streptococci. This was evidence that the material could act inside a living animal, not yet a human clinical trial. The seven-author paper itself contradicts the idea that the Oxford breakthrough belonged to Florey and Chain alone (Chain et al. 1940).
Oxford staff grew surface cultures in hundreds of vessels and processed enormous volumes for very small yields. Six women recruited to maintain cultures became known within the laboratory as the “penicillin girls”; a longer list of technicians was acknowledged in the 1941 report. Mary Ethel Florey later supervised clinical work at the Radcliffe Infirmary, military hospitals, and Birmingham Accident Hospital (History of Science Museum).
Early Patients
The Oxford team's report of 16 August 1941 described intravenous penicillin in five patients with staphylococcal or streptococcal infections, oral administration to one infant with a urinary infection, and local treatment in four eye infections. Most systemic cases had already received surgery, sulphonamides, transfusion, or other treatment. This was a detailed case series, not a randomised comparison, and the article does not document consent in the form later expected of clinical research (Abraham et al. 1941).
The first adult case illustrates both promise and scarcity. A 43-year-old police constable with widespread staphylococcal and streptococcal infection improved during five days of treatment. The team recovered active drug from his urine to reuse it, but the supply was exhausted on 17 February; his infection later worsened and he died on 15 March. The authors themselves cautioned that assessment was difficult because he also received blood transfusions and the dose and treatment period were inadequate.
Later cases supplied more persuasive therapeutic evidence, and the authors reported favourable responses in all ten. Yet their conclusion was properly narrower than later “miracle cure” memory: penicillin appeared to combine low toxicity with strong activity against a useful but limited range of bacteria, while dose, administration, purity, and supply still required investigation. The paper is unusually valuable because it states those uncertainties and names the collaborators and technicians who made the work possible.
Wartime Scale-Up
In July 1941 Florey and Heatley brought the production problem to the U.S. Department of Agriculture's Northern Regional Research Laboratory in Peoria, Illinois. USDA researchers improved the culture medium, screened more productive mould strains, and acted as a hub distributing strains and information. Industrial researchers then adapted aerated submerged fermentation and recovery methods for large tanks (American Chemical Society).
The U.S. Committee on Medical Research and, from 1943, the War Production Board coordinated pharmaceutical companies, laboratories, priorities, construction materials, and information. Roswell Quinn's archival study argues that government stewardship, intra-industry cooperation, and open scientific exchange—not one firm's proprietary process—were central to the wartime collaborative (Quinn 2013).
Early supplies were prioritised for military needs and selected civilian cases. In the United States, Chester Keefer's National Research Council committee rationed civilian penicillin while collecting clinical records. Production rose sharply in 1944, but “availability” remained specific to place, institution, and eligibility: a successful drug on paper was not the same as access for every patient.
Wartime publicity tied penicillin to wounded Allied servicemen, but its uses were broader, including streptococcal and staphylococcal infections, gonorrhoea, and syphilis caused by susceptible bacteria. The same military priorities that accelerated production also directed who received the scarce drug first. U.S. distribution restrictions ended in March 1945; general prescription sale in Britain began in June 1946 (American Chemical Society).
Resistance and Limits
Fleming's 1929 tests already showed that some bacterial groups were naturally insensitive. In December 1940, Edward Abraham and Ernst Chain reported an enzyme produced by a strain of B. coli—now Escherichia coli—that destroyed penicillin. The 1941 Oxford report also described laboratory selection of staphylococci able to tolerate higher concentrations. These observations did not predict every later resistance mechanism, but they rule out a story in which complete efficacy came first and resistance appeared only after careless postwar use (Abraham and Chain 1940; Abraham et al. 1941).
In his 11 December 1945 Nobel lecture, Fleming used a hypothetical case to warn that inadequate exposure could select resistant organisms. This is a retrospective public lecture, delivered after penicillin had become famous, not evidence that the 1928 plate foretold a global resistance crisis. It does show that resistance and dosage were explicit public concerns at the moment of commemoration (Fleming 1945).
Postwar abundance enlarged the issue. Pharmaceutical marketing, empirical prescribing, fixed-dose combinations, professional disagreement, and attempts to define “rational” antibiotic use shaped resistance policy as much as laboratory knowledge did. Penicillin's legacy therefore includes both effective treatment and an enduring struggle to preserve antimicrobial usefulness (Bud 2007; Podolsky 2015).
Credit and Memory
The 1945 Nobel Prize recognised Fleming, Chain, and Florey for the discovery of penicillin and its curative effect. That allocation fixed a memorable three-person story, but it did not encompass Heatley's assay and extraction, Abraham's purification and chemistry, Gardner's bacteriology, Jennings's biological testing, Fletcher's clinical administration, Mary Ethel Florey's later trial supervision, the production technicians, patients, USDA researchers, engineers, firms, or public officials (Nobel Prize 1945).
Correcting the heroic version need not make Fleming irrelevant. His work converted contamination into a named, published, reproducible phenomenon; the Oxford group made experimental and clinical medicine from it; and the wartime collaborative made large-scale supply. Observation, publication, purification, assay, animal protection, human treatment, fermentation, and distribution are all defensible meanings of “discovery,” but they should not be treated as the same event.
Chronology
Legacy
Penicillin substantially changed the prognosis of susceptible bacterial infections and helped make laboratory-guided drug treatment central to hospital medicine. Its production also supplied a model for later antibiotic screening, fermentation, pharmaceutical expansion, and government-industry collaboration. These consequences belong mainly to the 1940s and after, not to the plate alone.
The stronger historical claim is therefore also the more limited one: a significant 1928 observation became a transformative medicine through years of collective work under particular British and U.S. institutional and wartime conditions. Penicillin never treated all infections, benefit was never distributed automatically, and resistance accompanied the drug from its earliest experimental development. Continue with the broader history of antibiotics and penicillin or compare another laboratory-to-therapy transition in insulin therapy.
References
British Journal of Experimental Pathology 10, no. 3 (June 1929): 226–236. PMCID: PMC2048009. The contemporary experimental report, used for the plate observation, bacterial spectrum, stability, toxicity tests, nomenclature, and the modest therapeutic proposal. It does not document the later story's exact date or full contamination sequence.
Medical History 26, no. 1 (1982): 1–24. DOI: 10.1017/S0025727300040758. A historical reconstruction using surviving laboratory records, colleague testimony, and replication experiments. It is useful for separating contemporary documentation from later recollection, while some proposed details remain inferences.
The Lancet 236, no. 6104 (24 August 1940): 226–228. DOI: 10.1016/S0140-6736(01)08728-1. The seven-author primary report of Oxford's animal-protection experiments; evidence for action in infected mice, not yet clinical effectiveness in humans.
Nature 146 (28 December 1940): 837. DOI: 10.1038/146837a0. A brief primary communication on a penicillin-destroying bacterial enzyme, used to show that biochemical resistance mechanisms were under study before mass clinical use.
The Lancet 238, no. 6155 (16 August 1941): 177–189. DOI: 10.1016/S0140-6736(00)72122-2. The detailed contemporary report on culture, assay, purification, pharmacology, resistance, and ten early human cases. Its dramatic observations came from a small case series and should not be redescribed as a modern controlled trial.
Institutional history of the Oxford programme, used for Heatley's assay and extraction, the mouse work, production vessels, Gardner's resistance experiments, Abraham's chemistry, and Dorothy Crowfoot Hodgkin's crystallographic contribution.
Museum research profile identifying researchers and production workers, including the six women who maintained cultures, Mary Ethel Florey's clinical supervision, Margaret Jennings's toxicity work, and Arthur Sanders's operation of extraction equipment.
American Journal of Public Health 103, no. 3 (2013): 426–434. DOI: 10.2105/AJPH.2012.300693. An archival study of U.S. government stewardship, strain exchange, scientific coordination, industrial cooperation, and the wartime political economy of production.
International Historic Chemical Landmark account. Used for the Peoria programme, culture media and strain improvement, industrial fermentation, War Production Board coordination, wartime rationing, production growth, and U.S. and British civilian-release dates. Its commemorative language and simplified “first” claims are not adopted here.
Journal of Clinical Investigation 116, no. 9 (2006): 2311. DOI: 10.1172/JCI29920. A scholarly review used for the established roles of type-specific serum and sulphonamides before penicillin and for the institutional complexity of pre-antibiotic pneumonia treatment.
Oxford: Oxford University Press, 2008. Print ISBN 978-0-19-953484-5. A broad history of antimicrobial chemotherapy used to place Salvarsan, sulphonamides, penicillin, and later antibiotics in sequence without presenting 1928 as an empty starting point.
Oxford and New York: Oxford University Press, 2007. ISBN 978-0-19-925406-4; NLM ID 101302020. A major social history of discovery, production, the “penicillin” brand, postwar use, and resistance.
Baltimore: Johns Hopkins University Press, 2015. ISBN 978-1-4214-1593-2. A history of postwar prescribing, pharmaceutical promotion, clinical evidence, regulation, and attempts to respond to resistance.
Nobel Lecture, 11 December 1945. A retrospective primary source used for Fleming's public warning about underdosing and resistance. It was delivered after wartime success and celebrity had reshaped the discovery narrative.
Official award record for the joint prize to Fleming, Chain, and Florey. Used to document the award and its stated rationale, not as a complete account of contributors.