Penicillin

Penicillin is a type of drug called an antibiotic that can treat bacterial infections by killing the bacteria or making it difficult for the bacteria to grow. Before the availability of antibiotics, physicians could do little to help patients with bacterial infections, and many of those patients died of those infections. In 1928, Alexander Fleming, a Scottish physician, found a fungus growing in his lab that prevented the growth of certain bacteria. He termed the bacteria-killing substance penicillin. Later researchers built on Fleming’s findings and developed the substance into a drug, which became widely available after 1945. Penicillin was one of the first medications that could safely and effectively treat acute bacterial infections, such as staph infections and strep throat, as well as chronic bacterial infections such as syphilis. Additionally, by studying the mechanism of how penicillin works, researchers have created many other antibiotics. Penicillin and other antibiotics have allowed physicians to treat countless bacterial infections, and to develop new strategies to fight bacterial resistance to those antibiotics, saving the lives of millions.

1. Medicine Before Penicillin
2. Alexander Fleming's Discovery
3. The Oxford Group
4. Scaling Up Production
5. Impact of Penicillin
6. Learning How Penicillin Works
7. The Problem of Resistance

Medicine Before Penicillin

Before antibiotics, physicians could do very little for patients who had a bacterial infection. For centuries, doctors had used mercury as a treatment for syphilis, however many patients died from mercury poisoning rather than from syphilis. By 1910, doctors had access to an arsenic-based drug called Salvarsan as a treatment for syphilis. Salvarsan became a popular treatment for syphilis in its day but fell out of use because other drugs came along that were less toxic.

By the 1930s, physicians had access to drugs derived from synthetic dyes that could treat some types of bacterial infections. Called sulfa drugs, those medicines became extremely popular in the 1930s. Nevertheless, there were drawbacks to sulfa drugs, including difficulty in administrating them and toxic side effects. When a safer and more effective option became available in the form of penicillin, sulfa drugs faded from frontline use.

Alexander Fleming’s Discovery

Penicillin became widely available after 1945, but the roots of the drug's discovery date back to 1928. On 3 September of that year, Alexander Fleming, a Professor of Bacteriology at St. Mary’s Hospital Medical School in London, England, was sorting through petri dishes containing colonies of Staphylococcus, a bacterium that causes boils and sore throats, when a made a startling observation. He noticed that one dish had colonies of bacteria randomly scattered across the dish except for one section that had mold growing on it. The section with mold had no colonies of Staphylococcus around it. It appeared that the fungus was producing a substance that was inhibiting growth of the bacteria.

After that initial observation, Fleming began to study the mold in more in depth. He grew the mold in broth, or liquid growth medium, and then tested what effect the broth had on the growth of a variety of bacteria. To perform those tests, Fleming grew different bacteria on agar plates into which he poured some of the broth, which he called mold juice. Fleming found that his mold juice could kill a wide range of pathogenic bacteria including staphylococcus, streptococcus, pneumococcus, gonococcus, and meningococcus. Fleming published his findings on the bacteria-killing power of the mold juice in 1929 in the British Journal of Experimental Pathology. In that paper, he identified the mold as Penicillium rubrum, and called the antibacterial substance produced by the mold penicillin. For many years, there was disagreement among scientists over whether Fleming’s identification of the mold as Penicillium rubrum was correct. In 2011, a team of researchers led by Jos Houbraken in the Netherlands found that the mold Fleming grew was actually Penicillium rubens. Fleming concluded his 1929 paper by noting that penicillin could potentially be used as an antiseptic to treat bacterial infections. Fleming continued to research penicillin after 1929, but since he was a bacteriologist rather than a chemist, he was unable to chemically isolate a pure form of the molecule.   

The Oxford Group

In 1938, Howard Florey and Ernst Chain, professors of pathology at Oxford University in Oxford, England, and their colleagues revisited Fleming’s 1929 work and set out to study the chemical and biological properties of the substance that Fleming had termed penicillin. Over the course of several years, they developed ways to culture ample quantities of the Penicillium fungus in the lab, as well as methods to extract and purify the antibacterial substance. Florey and his colleagues devised a large fermentation vessel that allowed them to grow large volumes of the Penicillium fungus. A member of the Oxford team, Norman Heatley, developed a system to extract large amounts of penicillin from the culture medium. Edward Abraham, also a researcher at Oxford, then figured out how to extract and purify the penicillin using column chromatography, a laboratory technique used to separate components of liquid solutions. Once researchers could reliably extract penicillin, they were able to begin investigating its therapeutic benefits in cases of bacterial infection.

In 1940, Florey conducted experiments in mice that demonstrated penicillin’s ability to eradicate a virulent strain of Streptococcus bacteria. The researchers published their results in The Lancet in 1940. The article was one of the first to describe a curative treatment for bacterial infection. Specifically, Florey and his colleagues found that penicillin was effective in treating infections like staph infections, strep throat, and gas gangrene, which is a deadly infection that spreads rapidly throughout the body, causing tissue death.

In 1941, Albert Alexander, a British policeman, became the first human treated with Florey and colleagues’ penicillin. He presented with life-threatening infection of his eyes, face, and lungs, so physicians gave him penicillin to try to eradicate the infection. A few days after physicians injected him with penicillin, Alexander started to make a recovery that would have been almost impossible before the advent of penicillin. However, even though researchers were able to extract enough penicillin to conduct trials on mice, they were unable to extract enough to sustain penicillin treatment in a human. Supplies of penicillin ran out before Alexander’s infection was entirely gone, and he died a couple of days later.

Scaling Up Production

To make widespread distribution of penicillin possible, researchers needed to find a way to greatly increase its production, so in the summer of 1941, Florey and Heatley travelled to the US to try to enlist the American pharmaceutical industry’s assistance in producing penicillin. The researchers traveled to the US to find resources to make penicillin because the chemical factories in Britain were focused on supporting the country during World War II. When they arrived in the US, Florey and Heatley met with Robert Thom, an authority on the Penicillium fungus at the US Department of Agriculture. Thom directed them to the Department of Agriculture’s Northern Regional Research Laboratory, or ANRRL. At the ANRRL, researchers discovered numerous novel methods of increasing penicillin output from different Penicillium mold strains. The researchers shifted to growing the fungus in submerged cultures rather than using the conventional surface culture technique that the Oxford research team used. In a submerged culture, the producers grow the fungus in a large tank and constantly agitate it, giving the fungus access to nutrients needed for growth and increased yield. Scientists around the globe began testing for strains that would produce the most penicillin and communicated with the ANRRL about their results. A strain found in a cantaloupe in Peoria, Illinois, produced more penicillin than the one Fleming used. In 1946, researchers at the University of Wisconsin in Madison, Wisconsin, found that exposing a mutant of the Penicillium strain found in the cantaloupe to ultraviolet light further increased penicillin yield.

While Heatley helped researchers with increasing penicillin yield, Florey traveled around the US to interest pharmaceutical companies in the drug. Florey, along with Alfred Newton Richards, then vice president of medical affairs at the University of Pennsylvania in Philadelphia, Pennsylvania, communicated with Merck, Squibb, Lilly, and Pfizer, all pharmaceutical companies. In October 1941, Richards hosted a meeting in Washington, D.C., to plan a collaboration between the government and private company researchers to increase penicillin production. In December 1941, after the US joined World War II, industry partners agreed to research and mass produce penicillin. Mass production resulted in some difficulties because scientists needed to aerate and cool the mold, the mixture needed an anti-foaming agent, and researchers needed to extract penicillin at low temperatures. Researchers at pharmaceutical companies developed new technologies. In 1940, penicillin cost almost twenty US dollars per dose; by 1943, it cost fifty-five cents a dose in 1943. By September of 1943, the nation’s penicillin stock was large enough to treat infections among the entire Allied Armed Forces, which included the militaries of the US and United Kingdom. By 1944, scientists used penicillin as a primary treatment for British and US armed forces. Also in 1944, Pfizer opened the first commercial plant for penicillin production in Brooklyn, New York.

In 1945, Fleming, Chain, and Florey won the Nobel Prize in Medicine or Physiology for their work on the extraction, purification, and testing of penicillin, one of the first antibiotics.

Impact of Penicillin

In the 1940s, physicians began using penicillin to cure previously incurable diseases, including several sexually transmitted diseases. For example, during World War II, the US Army was experiencing high rates of syphilis, so researchers sought to use penicillin as treatment for that sexually transmitted bacterial infection. Though the military attempted to control the spread of syphilis by educating the soldiers, the epidemic continued. A group of researchers, including Joseph Earle Moore, J. F. Mahoney, and their collogues, all part of the Penicillin Panel of the Subcommittee on Venereal Disease Division of the National Research Council, investigated the efficacy of penicillin at treating syphilis. In a 1944 paper titled “The Treatment of Early Syphilis with Penicillin: A Preliminary Report of 1,418 Cases,” Moore and his colleagues demonstrated that penicillin significantly improved symptoms in patients by helping heal lesions and decreasing the concentration of the syphilis-causing bacteria Treponema pallidum in those patients.

Penicillin was very effective at treating infectious diseases such as syphilis and staph infections, but in the coming decade, researchers realized that penicillin was not effective against other kinds of bacterial infections, such as tuberculosis. In the 1950s, penicillin became characterized as a narrow-spectrum antibiotic, meaning that it works only on a very narrow range of bacteria. For example, it was ineffective against bacteria that did not have a lot of peptidoglycans in their cell walls since its primary mode of action as an antibiotic is to block the linkage of peptidoglycans to each other.  

As a result of those limitations, researchers began working on completely new antibiotics using the penicillin extraction method and structure as a guide. For example, in 1953, researchers isolated vancomycin, an antibiotic that can treat some of the infections that penicillin cannot treat. In addition to the new antibiotics they created, researchers have also made penicillin-based antibiotics that are slightly modified versions of penicillin.

Learning How Penicillin Works

The 1950s and 1960s witnessed progress in understanding how penicillin kills bacteria. In the mid-1950s, scientists including James Park, Jack Strominger, and Joshua Lederberg learned that penicillin somehow interfered with the process by which bacteria synthesized new cell walls. In the 1965, scientists E.M. Wise, J.T. Park, D.J. Tipper, and Strominger demonstrated that penicillin works by binding to and inhibiting an enzyme in bacteria that links together molecules in the bacterial cell wall called peptidoglycans. The interlinked peptidoglycan molecules are essential for maintaining the integrity of the bacterial cell wall. Without the ability to link peptidoglycans, dividing bacteria cannot form new cell walls. Without cells walls, the bacteria can’t resist water pressure, so they swell up and burst.

Scientists also learned that the chemical structure of penicillin contributes to its ability to treat bacterial infections. Penicillin has a core component called the beta-lactam ring, which contributes to its mechanism of action. The four-membered beta-lactam ring can bind to the peptidoglycan enzyme in the bacterial cells and stop its action.

The Problem of Resistance

The very success of penicillin as a cure for previously incurable infections has resulted in the problem of antibiotic resistance. Antibiotic resistance is when antibiotics become ineffective against certain bacteria due to overuse and misuse. In the case of penicillin, resistant bacteria produce an enzyme called beta-lactamase, which breaks down a bond in the four-membered ring in penicillin. In doing so, they effectively block penicillin’s action, rendering it useless. Sometimes, physicians can prescribe beta-lactamase inhibitors that block breakdown to ensure that penicillin works. For example, in 1972, researchers found a potential beta-lactamase inhibitor, clavulanic acid. In 1981, scientists in the UK introduced Augmentin, which is a combination of amoxicillin, an oral antibiotic, and clavulanic acid to counter antibiotic resistance and allow for the targeting of a broader range of infectious bacteria. However, resistant bacteria continuously evolve new ways of surviving in their hosts, creating a continuous cycle of penicillin and antibiotic research and development.

Researchers continue to investigate ways to mitigate the problem of antibiotic resistance. For example, in 2021, Thomas Durand-Reville, a researcher at Entasis Therapeutics in Waltham, Massachusetts, and colleagues developed antibiotics called diazabicyclooctane inhibitors to prevent resistant bacteria from breaking down penicillin and rendering it ineffective. Also in 2021, Marco Terenni, an Italian bacteriology researcher, and his colleagues described the synthesis of new kinds of antibiotics that may be effective against multi-drug resistant bacteria, which means that those new antibiotics could kill bacteria that are resistant to multiple antibiotics. In 2023, researchers at the Massachusetts Institute of Technology in Cambridge, Massachusetts, used an artificial intelligence model capable of designing novel antibiotics to develop antibiotics that could kill methicillin-resistant Staphylococcus aureus, or MRSA.

While antibiotic resistance remains a challenge, the benefits of antibiotics to modern medicine are evident every day. According to a report from the Centers for Disease Control and Prevention in 2016, doctors prescribe over 270 million antibiotics per year in the US, including around sixty-three million units of penicillin. Antibiotics like penicillin cure millions of infections and save thousands of lives annually. By launching a new era of medicine, Fleming’s accidental discovery of what he called mold juice has had a lasting legacy.