The history of penicillin

Most stories about the history of penicillin begin with Alexander Fleming returning from holiday one summer, in September 1928, to find that one of the Petri dishes that he had failed to place in an incubator before his departure had become contaminated with a mould. The Petri dish contained a culture of Staphylococcus aureus, a round-shaped bacteria that is a common cause of boils, sore throats and abscesses. What was particularly striking was there appeared to be clear zones around the mould where the bacteria had grown previously.

Figure 2.1.1: Taken in 1928, this photograph shows the petri dish that Fleming observed which contained both the mould (Penicillium colony) and the staphylococci bacteria. The clear zone around the mould that Fleming found was where bacteria had stopped growing (Credit: Fleming, 1929). The mould was later identified to be Penicillium notatum by Charles Thom, an American microbiologist and mycologist who was a expert on the taxonomy of the Penicillium family.

Fleming identified the contaminant to belong to a species of mould known as Penicillium, which grows in a diverse range of habitats, from soil to vegetation to air, indoor environments and various food products. On further investigation Fleming found that the mould appeared to produce an antibacterial substance and that this could be grown in a broth and then extracted with a filter. He called the filtered agent 'penicillin'. Subsequent experiments showed that this filtered substance could destroy both staphylococci and other gram-positive pathogens even when diluted by as much as 800 times. Furthermore, it appeared to have no toxic effects when injected into rabbits and mice. Fleming later discovered that there were only a handful of Penicillium strains that produced such an antibacterial substance. By the beginning of 1929 Fleming had started testing crude preparations of penicillin as a topical treatment for surface infections in some patients. In June 1929 Fleming published his first results with penicillin, with the suggestion that it could provide a useful treatment for infections with penicillin-sensitive microbes. Little attention, however, was paid to his work until the rise of sulphonamides in the mid-1930s (Fleming, 1945). Click here for the early clinical applications of Fleming's penicillin.

Figure 2.1.2: Alexander Fleming at work in his laboratory at St Mary's Hospital, 1944, Ministry of Information Photo Division Photographer (Credit: Imperial War Museum). Fleming (1881-1955) was born in Scotland and trained in medicine at St Mary's Hospital in London. By the time he made his discovery of penicillin he had a position in the Inoculation Department at St Mary's Hospital and was a professor of bacteriology at the University of London. His work on penicillin emerged on the back of his research to understand microbes which caused diseases such as tetanus and gangrene, and search for antibacterial substances to combat them. He first got interested in this field as a result of his experiences as a physician during World War I, during which time he saw many soldiers die from sepsis resulting from infected wounds. One of the first antibacterial substances Fleming discovered was lysozyme, an enzyme present in many secretions, including tears, saliva and mucus. Despite being able to obtain large amounts of lysozyme from egg whites, Fleming found it was only effective against a small number of harmless bacteria so realised it had little therapeutic potential.

What is often forgotten in the legend told about Fleming, is that he was not the first to notice the antibacterial effects of Penicillium or to test it out as a treatment. Indeed, a number of investigators observed the same phenomenon before him and had conducted experiments to assess Penicillium's therapeutic value. The key contributions that Fleming made was his detailed characterisation of the antibacterial substance he found in the mould and his efforts to preserve mould. Importantly, he deposited it in a culture collection, which allowed other investigators to pursue its antibacterial substance and develop it as a clinical product (Wainwright). Click here for early Penicillium investigators.

It took many years before penicillin was transformed into a drug. One of the major challenges was that the compound was very unstable. Fleming himself discovered that blood rapidly inactivated the substance when it was given in fluid form. Another problem that Fleming noted was that the antibacterial activity of the penicillin extracts disappeared fourteen days after they were stored at room temperature (Hare).

More was achieved by Howard Florey and Ernst Chain based at the William Dunn School of Pathology, Oxford University. They first began studying penicillin in 1938. This they did with the help of a sample from Fleming's mould. The sample had by chance been obtained some years before by George Dreyer, Florey's predecessor, and stored in the Dunn's School's culture collection. When Florey and Chain started the project they had little intention of turning penicillin into a drug. As Chain himself later admitted 'the possibility that penicillin could have practical use in clinical medicine did not enter our minds when we started our work on penicillin. A substance of the degree of instability which penicillin seemed to possess according to the published facts [did] not hold out much promise for practical application.' Florey and Chain's work on penicillin had started off as a much wider project to understand the biochemical and biological nature of different inhibitory agents produced by different microorganisms like bacteria, fungi and yeasts. Penicillin was thus just one of a number substances they set out to investigate. It was included after Florey discovered the substance after reading Fleming's published paper. (Chain). Florey probably first learnt about the antibacterial properties of penicillin much earlier than Chain, because he had sat on the editorial board of the British Journal of Experimental Pathology when it took the decision to publish Fleming's first paper on the subject (Alharbi et al). He then came across the substance again when he joined Sheffield University which brought him into contact with Cecil Paine, a physician who in the early 1930s successfully used a penicillin culture, originally obtained from Fleming, to treat patients with eye infections. Click here for more on Paine.

Figure 2.1.3: Howard Florey, 1945 (Credit: The Nobel Prize). Born in Malvern, a southern suburb of Adelaide, South Australia, Florey (1898-1968) studied medicine at the University of Adelaide and at Oxford universities. He then held teaching and research posts at Cambridge and Sheffield universities. In 1935 he was appointed the professor of pathology at Oxford, where he remained until 1962.

By March 1940 Chain had managed, with the help of Edward Penley Abraham, another chemist, to purify enough penicillin to be tested in two mice they had infected with deadly Streptococcus. So encouraged were they by the results in these mice that the team then tested it in 50 more mice deliberately infected with the same bacteria. Half the mice who were given the penicillin survived while the others left untreated died from sepsis.

Armed with the promising results, the team turned their attention to testing it in patients. Such testing posed a huge challenge because they still did not have the means to produce purified penicillin in large quantities. It was estimated that it would take about 2,000 liters of mould culture fluid to get enough penicillin to treat a single case of sepsis in a human. The task of production was assigned to Norman Heatley, a biochemist who had joined Florey's department in 1936. In order to scale up production Heatley used every container, bottle and bedpan he could find to grow vats of penicillin mould and then suctioned off the fluid to begin the purification process.

By February 1941 the Oxford team had enough purified penicillin to treat the first patient. Sadly they did not have enough of it to see him through to full recovery. Thereafter, they restricted their use of the drug in sick children who did not require such large doses. At the same time they began a search for a more productive means to produce the drug. They launched their search in the summer of 1941 with the help of Charles Thorn and Jackson Moye and other American scientists at the US Department of Agriculture. By this point the mass production of penicillin had become a major priority for British and American governments who believed such a drug would help them combat infections in soldiers fighting in the Second World War. The effort to produce penicillin soon roped in 21 companies, five academic groups and several government agencies. The collaboration transformed the production of penicillin from a low-yielding, labour-intensive method of growing crude penicillin in any container to the fermentation of highly refined penicillin in 10,000-gallon tanks (Quinn).

Figure 2.1.4: Ernest Chain, 1944 (Photo by Wolfgang Suschitzky. Credit: National Portrait Gallery). Born in Berlin, Germany, Chain completed a degree in biochemistry at Friedrich Wilhelm University in 1930 and then took a research position at the Institute of Pathology, Charité Hospital, Berlin. Being Jewish he was forced to flee to England three years later when the Nazis seized power. Once in England he completed a PhD at Cambridge University and then in 1935 joined Florey's team in Oxford.

Figure 2.1.5: Penicillin timeline.


Alharbi, SA, et al (2014) 'What if Fleming had not discovered penicillin?', Saudi Journal of Biological Sciences, 21: 289-93.Back

Chain, E (1971) 'Thirty Years of Penicillin Therapy', Proceedings of the Royal Society of London. Series B, Biological Sciences, 179/1057, A Discussion on Penicillin and Related Antibiotics-Past, Present and Future: 293-19.Back

Hare, R (1986) ‘New light on the history of penicillin’, Medical History, 26: 1-24.Back

Fleming, A (1929) 'On the Antibacterial Action of Cultures of a Penicillium, with Special Reference to their Use in the Isolation of B. influenzae', British Journal Experimental Pathology, 10/3: 226-36.Back

Fleming, A (1945) 'Penicillin', Nobel Lecture, 11 Dec.Back

Quinn, R (2013) 'Rethinking antibiotic research and development: World War II and the penicillin collaborative', American Journal of Public Health, 103/3: 426-34.Back

Wainwright, M (2000) 'Andre Gratia (1893-1950): Forgotten pioneer of research into antimicrobial agents', Journal of Medical Biography, 8: 39-42.Back

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