Penicillin: Discovery, Benefits and Resistance

Penicillin is a drug used to fight bacterial infection. Its accidental discovery ushered in a new age of medicine. It was hailed as a “miracle drug” that would eradicate infectious diseases. Today, there are many types of natural and synthetic types of penicillin, which are used to treat a wide range of ailments. However, over the years, some bacteria have become resistant to penicillin, making some infections difficult to treat.

It isn’t really known who first realized that mold contained medicinal qualities, but it is acknowledged that ancient Egyptians would poultice wounds with moldy bread, according to the American Chemical Society (ACS).

Alexander Fleming, a professor of bacteriology in London, is credited with discovering penicillin in 1928. Returning from vacation, he started cleaning up his messy lab and noticed that some petri dishes containing Staphylococcus bacteria had been contaminated with a mold, Penicillium notatum, which was inhibiting the growth of the bacteria, according to Dr. Howard Markel in a column for PBS NewHour. Fleming researched the juice produced by the mold and determined that it killed many types of bacteria. His team then went on to isolate pure penicillin from the mold juice.

“When I woke up just after dawn on September 28, 1928, I certainly didn’t plan to revolutionize all medicine by discovering the world’s first antibiotic, or bacteria killer. But I guess that was exactly what I did,” Fleming later wrote about his discovery.

Fleming didn’t have the resources to fully develop his discovery. Other bacteriologists tried to purify penicillin but failed. Finally, in 1939, Howard Florey, a pathology professor at Oxford University, read Fleming’s paper in the British Journal of Experimental Pathology, and he and his colleagues worked to purify and create useable penicillin.

After churning out around 132 gallons (500 liters) of mold filtrate per week and testing on animals, they were finally able to try the new drug on a human. On February 12, 1941, Albert Alexander got the first dose of penicillin, according to the ACS. The treatment started to heal him of a life-threatening infection in just a few days. Unfortunately, the Oxford team ran out of the drug before Alexander was completely healed, and he died.

A close-up of penicillin growing in a flask, circa 1943.
A close-up of penicillin growing in a flask, circa 1943.

Credit: Everett Historical/Shutterstock


The first successful treatment happened a year later in 1942. It was given to Anne Miller, a patient at New Haven Hospital in Connecticut who had suffered a miscarriage and developed an infection that led to blood poisoning.

During World War II, penicillin was mass-produced and used to fight infections among soldiers. Throughout history, infections had killed more soldiers than battle injuries, Markel wrote. “In World War I, the death rate from bacterial pneumonia was 18 percent; in WWII, it fell to less than 1 percent.”

In 1945, Fleming, Florey and Florey’s teammate, Ernst Chain, received the Nobel Prize in Physiology or Medicine for their discovery of penicillin. [The 10 Noblest Nobel Prize Winners of All Time]

Penicillin is given to patients with an infection caused by bacteria. As an antibiotic, it inhibits the growth of bacteria or kills it. It does this by preventing bacterial enzymes from creating cell wall growth. It also activates other enzymes so that they will break down the cell walls of microorganisms, as well, according to Encyclopedia Britannica.

Sometimes penicillin is also prescribed to help medical problems not related to bacterial infections, such as leptospirosis, chlamydia in pregnant women, helicobacter pylori-associated gastritis or peptic ulcer disease, gas gangrene, Lyme disease and typhoid fever, according to the Mayo Clinic.

Different kinds of penicillin are used for various infections. Some types of penicillin are amoxicillin, ampicillin, penicillin G and penicillin V.

Though penicillin has saved many lives, it isn’t always helpful for everyone. For example, some people have penicillin allergies that can cause hives, rashes, itching, anaphylaxis and other symptoms.

Beyond allergies, penicillin is becoming less useful over time. At least 2 million people in the United States become infected with bacteria that are resistant to antibiotics each year, and at least 23,000 people die as a result, according to the Centers for Disease Control and Prevention (CDC).

Simply using antibiotics creates resistance, according to the CDC. While antibiotics kill bacteria causing illness, they also kill “good” bacteria that protect the body from infection. The drug-resistant bacteria grow and take over, and some bacteria give their drug resistance to other bacteria. Resistant germs spread to other patients from unclean hands or surfaces.

For this reason, antibiotics should only be used to treat infections, and should not be prescribed for viruses, according to the Mayo Clinic.

And yet, many sore throats and upper respiratory infections that are caused by viruses are often prescribed antibiotics to treat these illnesses because it is a perceived quick fix, said Dr. Saul R. Hymes, medical director for Pediatric Antimicrobial Stewardship at Stony Brook Children’s Hospital.

“Overall, there is a major problem with inappropriate antibiotic prescribing in the United States,” said Hymes. “Recent studies by Katherine Fleming-Dutra and Adam Hersh in 2016 have shown anywhere from 30 to 50 percent of all outpatient prescriptions for antibiotics for common conditions like ear infections, sore throat and other upper respiratory-type infections are inappropriate.”