Penicillin was discovered by accident after a bacteriologist left his lab bench materials out during a summer vacation and mold invaded his petri dishes.

Alexander Fleming, Howard Florey, and Ernst Chain received the 1945 Nobel Prize in Physiology or Medicine for discovering and developing penicillin.

Alexander Fleming’s discovery of penicillin revolutionized modern medicine. But the same man who pioneered the development of antibiotics also recognized that bacteria could make sntibiotics obsolete if they were used irresponsibly. This story sheds light on Fleming’s discovery—and on his prophetic warning about antibiotic resistance.

In 1939, a team at Oxford—including Howard Florey, Ernst Chain, and Norman Heatley—revived Fleming’s forgotten discovery. Using makeshift equipment like bedpans and milk churns, they purified enough penicillin to prove it could treat deadly infections.

In 1943, a moldy cantaloupe found at a market in Peoria, Illinois, yielded a strain that produced six times more penicillin. Though often credited to lab worker “Moldy Mary” Hunt, accounts differ on who actually brought in the fruit.

Experts widely rank penicillin’s discovery among the most important advances in medicine. It launched the antibiotic era, transformed once-deadly infections into treatable illnesses.

When penicillin became widely available in the 1940s, newspapers and doctors alike celebrated it as a “wonder drug” that could cure infections once considered fatal.

In Oxford during the early 1940s, six female technicians—later dubbed the “Penicillin Girls”—worked long hours tending mold cultures and extracting tiny amounts of penicillin.

Despite its promise, US production of penicillin remained minimal in 1942—enough to treat fewer than 100 patients nationwide. Within two years, output expanded into millions of doses to supply troops for D-Day.

Since its introduction in the 1940s, penicillin and related antibiotics are estimated to have saved around 500 million lives worldwide—making it one of the most consequential medical breakthroughs in human history.

By 1943, the US War Department made penicillin its second-highest priority—just after the Manhattan Project. Producing enough of the antibiotic for the D-Day invasion became a central mission of Allied science and industry.

There are over 300 species of Penicillium. The mold that produces the lifesaving antibiotic is a close relative to those used to make blue cheeses like Roquefort and Stilton and to flavor some types of ham.

Before antibiotics, bacterial pneumonia killed about 18% of infected soldiers in World War I. By World War II, penicillin cut that death rate to less than 1%.

By June 1944, Allied stockpiles included 2.3 million doses of penicillin—enough to ensure that every soldier wounded during the pivotal Normandy landings could receive treatment.

In the early 20th century, pneumonia was a top cause of death worldwide, often fatal without effective treatment. Penicillin turned a once deadly infection into one of the most treatable bacterial diseases.

Anna Dumitriu's bioart piece was created to commemorate the 75th anniversary of the first use of penicillin in a human patient and intends to raise awareness about the rapid development of antibiotic-resistant pathogens by using bacteria that have essentially been transformed into their pre-antibiotic era state.

The pathogen was isolated by the Italian physician Filippo Pacini in Florence, Italy, though his discovery was largely ignored in favor of the popular miasma—bad air—theory of disease at the time. The pathogen was separately isolated about three decades later by German microbiologist Robert Koch.

In 1856, a chemist accidentally discovered mauveine, the world's first synthetic dye, while trying to make quinine to treat malaria. The synthetic dyes that followed helped reveal germs under microscopes, paving the way for modern imaging techniques and breakthrough treatments, such as antibiotics.

The vast majority of bacterial treatments were developed during the "Golden Age of Antibiotics," an era of rapid innovation and drug discovery that led to the reduction of millions of deaths worldwide. Since 1970, only eight new antibiotic classes have been discovered.

Between 1840 and 1883, scarlet fever was among the leading causes of childhood death in the United States, with case fatality rates ranging from 15% to 30%. Today, thanks to antibiotics like penicillin, the mortality rate is below 1%.

Koch was one of the first scientists to isolate the bacterium that causes cholera while investigating an outbreak in Egypt in 1883. He went on to advise about rules to control cholera outbreaks, which formed the basis of the disease control approaches and water hygiene techniques still used today.

Borrelia bacteria existed long before any US biological weapons program—or human presence in North America. One study comparing genomes of the bacteria behind Lyme disease collected samples of the bacteria over three decades and calculated that the bacterium has been in North America longer than humans, at least 60,000 years. Other work found related bacteria preserved in amber from millions of years ago.

For centuries, Type 1 diabetes was fatal. The 1920s "discovery" of insulin netted two of its creators—Frederick Banting and his boss, John Macleod—a Nobel prize. Separately, the German doctor Georg Zuelzer synthesized an effective version of the life-saving drug years earlier but was interrupted by World War I.

The show blends medical history with storytelling and science. In Episode 50, the hosts trace the dramatic origins of antibiotics—from Fleming's moldy petri dish to Florey's wartime labs—and explore their lasting impact on health.

Popularized by Aristotle in the 4th century BCE, spontaneous generation was used to explain phenomena like mice appearing in seemingly sealed grain storage. The invention of the compound microscope in the late 16th century led to the identification of cells as the basic unit of life, but it was not until 1855 that their origin from preexisting cells was established.

The chance encounter around 5,500 years ago laid the groundwork for cultured milk products like yogurt and cheese. Over time, microbes evolved in tandem with goats, sheep, and wheat to give us the wide variety of cheeses that we enjoy today.

When a can of ground beef and pork spoiled despite attempts to sterilize it with gamma radiation, researcher Arthur Anderson isolated the bacteria in the food and discovered Deinococcus radiodurans. The polyextremophile has since been found on the walls of nuclear reactors and overcomes radiation damage through highly optimized DNA repair mechanisms.

As part of government research, a group of young men were paid to eat standard American food—replete with food additives like borax and formaldehyde—which revealed the dangers of unregulated food. The work was led by the first FDA commissioner, Harvey Wiley, who helped end the "century of the great stomachache."

When they became ill—one with mild diarrhea and the other with severe cholera—researchers pointed to that as proof that the pathogen caused the disease.

Germ theory of disease is based on the concept that many diseases are caused by infections with microorganisms, typically only visualized under high magnification. Read this general overview to understand the basic framework which allowed for development of vaccines.

Scientists learned it was a microbial immune system that could be repurposed to protect dairy cultures from viruses. Today, nearly all yogurt is made with CRISPRized bacteria, as are genetically modified crops like herbicide-resistant corn, wheat, and soy.

Until the mid-1900s, most scientists believed genes were made of proteins, which were known to act as enzymes, hormones, and other chemicals that mediated an organism's traits. The Avery-MacLeod-McCarty and that benign bacteria could be made lethal, where the inherited factor that caused bacterial transformation contained DNA.

The Berkeley Pit, an open-pit copper mine in Butte, Montana, that ceased operations in 1982 and is now filled with highly acidic water, is home to various species of fungi and yeast. These extremophiles produce unique compounds that may have anti-inflammatory benefits and have already been used to create an antibiotic for staph infections.

In 1896, Henri Becquerel had been exploring phosphorescence—the emission of light of one color after an object is exposed to another color. He expected these emissions to come from objects exposed to sunlight, but he observed emissions after an overcast day.

Unlike humans, bacteria rapidly make genetic changes in response to their environment, including creating defense against antibiotics. Furthermore, these defenses are passed on to their future generations and can even be shared with neighboring bacteria through horizontal gene transfer.

While investigating samples taken from within and around the hot springs at Yellowstone National Park, microbiologist Thomas Brock discovered Thermus aquaticus, a microorganism that thrived in hot water. It contained an enzyme called Taq polymerase, a critical molecule in polymerase chain reaction—a molecular photocopier that amplifies genetic signals to improve medical diagnostics.

Before the technology behind vaccinations was discovered, some keen observers of medicine around the globe noticed how previous infections could impact future ones. Learn about the techniques early physicians used before they had vaccines.

For centuries, the miasma theory, which held that illnesses were caused by clouds of "bad air" produced by decaying organic matter, was the accepted explanation for the spread of disease. The development of microscopes and the subsequent technology to isolate bacteria and test disease spread in mice greatly contributed to contagionists overturning miasmatists.

Developed by researchers at Hebrew University, the method involves the firefly enzyme luciferase, which emits light from within bacteria expressing when they are in the presence of acetic acid vapors produced by wine. The process provides affordable, on-site, real-time monitoring of fermentation quality.