Penicillin is a crucial antibiotic derived from the Penicillium mold, first observed by Alexander Fleming in 1928. It works by inhibiting bacterial cell wall synthesis, making it effective against many common bacterial infections without harming human cells. Initially difficult to produce in large quantities, Howard Florey and Ernst Boris Chain later developed methods for its isolation and purification, leading to its therapeutic use by 1941. Penicillin revolutionized the treatment of bacterial infections, though some bacteria have developed resistance. Common side effects include allergic reactions.

Who discovered penicillin?

The discovery of penicillin is credited to Scottish bacteriologist Alexander Fleming in 1928. Fleming observed that a mold, later identified as Penicillium notatum , had contaminated a culture plate of Staphylococcus aureus bacteria and inhibited the bacteria's growth. He realized the mold produced an antibiotic substance, which he named penicillin. While Fleming made the initial discovery, the significance of penicillin was not fully recognized until over a decade later. British biochemist Ernst Boris Chain and Australian pathologist Howard Florey isolated and purified penicillin in the late 1930s, making it available for therapeutic use by 1941. Their work, along with Fleming's discovery, led to the antibiotic revolution and earned them a share of the 1945 Nobel Prize for Physiology or Medicine.

How does penicillin work to fight infections?

Penicillin works by inhibiting bacterial cell wall synthesis. It targets enzymes responsible for building and maintaining the protective outer layer of bacteria. By disrupting this process, penicillin weakens the cell wall, leading to the rupture and death of the bacteria. This mechanism is specific to bacteria and does not harm human cells, as human cells lack cell walls. Penicillin was discovered by Alexander Fleming in 1928 and later developed for therapeutic use by Howard Florey and Ernst Boris Chain .

What kinds of diseases are treated with penicillin?

Penicillin is an antibiotic used to treat a variety of bacterial infections. It is effective against infections caused by gram-positive bacteria, such as streptococcal sore throat, tonsillitis, and certain types of endocarditis. Penicillin is also used to treat syphilis and meningococcal infections. Semisynthetic penicillins, like ampicillin, have a broader spectrum of activity and are effective against some gram-negative bacteria, making them useful for treating infections of the respiratory and urinary tracts, as well as meningitis and gonorrhea. Penicillin works by inhibiting bacterial cell wall synthesis, which is crucial for bacterial survival. While generally safe, the most common side effect is hypersensitivity reactions, ranging from mild rashes to severe anaphylaxis.

Why is penicillin known as an antibiotic?

Penicillin is known as an antibiotic because it is a chemical substance produced by a living organism, specifically the Penicillium mold, that is detrimental to other microorganisms, particularly bacteria. Discovered by Alexander Fleming in 1928, penicillin inhibits bacterial cell wall synthesis, effectively killing bacteria without harming human cells. This property makes it a crucial tool in treating bacterial infections.

What challenges, like resistance, are faced when using penicillin today?

While penicillin remains a vital antibiotic, its effectiveness is challenged by bacterial resistance. Some bacteria, like certain strains of Staphylococcus , have developed mechanisms to counteract penicillin. These include producing enzymes such as \u03b2-lactamase (penicillinase), which breaks down the penicillin molecule, or altering cell wall receptors, reducing the drug's ability to enter bacterial cells. This has led to the development of penicillinase-resistant penicillins, though some bacteria have also developed resistance to these. The overuse of antibiotics has accelerated the proliferation of these resistant strains, making some infections difficult to treat.

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Key People:: Alexander Fleming; Howard Walter Florey, Baron Florey; Sir Ernst Boris Chain; Robert Burns Woodward; Dorothy Hodgkin

Related Topics:: Today in History—September 3: Alexander Fleming Finds Penicillin; Methicillin; ampicillin; Penicillin G; semisynthetic penicillin

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Top Questions

What is penicillin?
Penicillin is a crucial antibiotic derived from the Penicillium mold, first observed by Alexander Fleming in 1928. It works by inhibiting bacterial cell wall synthesis, making it effective against many common bacterial infections without harming human cells.

Initially difficult to produce in large quantities, Howard Florey and Ernst Boris Chain later developed methods for its isolation and purification, leading to its therapeutic use by 1941. Penicillin revolutionized the treatment of bacterial infections, though some bacteria have developed resistance. Common side effects include allergic reactions.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Who discovered penicillin?
The discovery of penicillin is credited to Scottish bacteriologist Alexander Fleming in 1928. Fleming observed that a mold, later identified as Penicillium notatum, had contaminated a culture plate of Staphylococcus aureus bacteria and inhibited the bacteria's growth. He realized the mold produced an antibiotic substance, which he named penicillin.

While Fleming made the initial discovery, the significance of penicillin was not fully recognized until over a decade later. British biochemist Ernst Boris Chain and Australian pathologist Howard Florey isolated and purified penicillin in the late 1930s, making it available for therapeutic use by 1941. Their work, along with Fleming's discovery, led to the antibiotic revolution and earned them a share of the 1945 Nobel Prize for Physiology or Medicine.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does penicillin work to fight infections?
Penicillin works by inhibiting bacterial cell wall synthesis. It targets enzymes responsible for building and maintaining the protective outer layer of bacteria. By disrupting this process, penicillin weakens the cell wall, leading to the rupture and death of the bacteria. This mechanism is specific to bacteria and does not harm human cells, as human cells lack cell walls. Penicillin was discovered by Alexander Fleming in 1928 and later developed for therapeutic use by Howard Florey and Ernst Boris Chain.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What kinds of diseases are treated with penicillin?
Penicillin is an antibiotic used to treat a variety of bacterial infections. It is effective against infections caused by gram-positive bacteria, such as streptococcal sore throat, tonsillitis, and certain types of endocarditis. Penicillin is also used to treat syphilis and meningococcal infections.

Semisynthetic penicillins, like ampicillin, have a broader spectrum of activity and are effective against some gram-negative bacteria, making them useful for treating infections of the respiratory and urinary tracts, as well as meningitis and gonorrhea.

Penicillin works by inhibiting bacterial cell wall synthesis, which is crucial for bacterial survival. While generally safe, the most common side effect is hypersensitivity reactions, ranging from mild rashes to severe anaphylaxis.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Why is penicillin known as an antibiotic?
Penicillin is known as an antibiotic because it is a chemical substance produced by a living organism, specifically the Penicillium mold, that is detrimental to other microorganisms, particularly bacteria. Discovered by Alexander Fleming in 1928, penicillin inhibits bacterial cell wall synthesis, effectively killing bacteria without harming human cells. This property makes it a crucial tool in treating bacterial infections.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What challenges, like resistance, are faced when using penicillin today?
While penicillin remains a vital antibiotic, its effectiveness is challenged by bacterial resistance. Some bacteria, like certain strains of Staphylococcus, have developed mechanisms to counteract penicillin. These include producing enzymes such as \u03b2-lactamase (penicillinase), which breaks down the penicillin molecule, or altering cell wall receptors, reducing the drug's ability to enter bacterial cells. This has led to the development of penicillinase-resistant penicillins, though some bacteria have also developed resistance to these. The overuse of antibiotics has accelerated the proliferation of these resistant strains, making some infections difficult to treat.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

penicillin, one of the first and still one of the most widely used antibiotic agents, derived from the Penicillium mold. In 1928 Scottish bacteriologist Alexander Fleming first observed that colonies of the bacterium Staphylococcus aureus failed to grow in those areas of a culture that had been accidentally contaminated by the green mold Penicillium notatum. He isolated the mold, grew it in a fluid medium, and found that it produced a substance capable of killing many of the common bacteria that infect humans. Australian pathologist Howard Florey and British biochemist Ernst Boris Chain isolated and purified penicillin in the late 1930s, and by 1941 an injectable form of the drug was available for therapeutic use.

(Read Alexander Fleming’s 1929 Britannica essay on antiseptics.)

The several kinds of penicillin synthesized by various species of the mold Penicillium may be divided into two classes: the naturally occurring penicillins (those formed during the process of mold fermentation) and the semisynthetic penicillins (those in which the structure of a chemical substance—6-aminopenicillanic acid—found in all penicillins is altered in various ways). Because it is possible to change the characteristics of the antibiotic, different types of penicillin are produced for different therapeutic purposes.

Why you should finish your prescribed antibiotics

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Antibiotic: Penicillins

The naturally occurring penicillins, penicillin G (benzylpenicillin) and penicillin V (phenoxymethylpenicillin), are still used clinically. Because of its poor stability in acid, much of penicillin G is broken down as it passes through the stomach; as a result of this characteristic, it must be given by intramuscular injection, which limits its usefulness. Penicillin V, on the other hand, typically is given orally; it is more resistant to digestive acids than penicillin G. Some of the semisynthetic penicillins are also more acid-stable and thus may be given as oral medication.

All penicillins work in the same way—namely, by inhibiting the bacterial enzymes responsible for cell wall synthesis in replicating microorganisms and by activating other enzymes to break down the protective wall of the microorganism. As a result, they are effective only against microorganisms that are actively replicating and producing cell walls; they also therefore do not harm human cells (which fundamentally lack cell walls).

Some strains of previously susceptible bacteria, such as Staphylococcus, have developed a specific resistance to the naturally occurring penicillins; these bacteria either produce β-lactamase (penicillinase), an enzyme that disrupts the internal structure of penicillin and thus destroys the antimicrobial action of the drug, or they lack cell wall receptors for penicillin, greatly reducing the ability of the drug to enter bacterial cells. This has led to the production of the penicillinase-resistant penicillins (second-generation penicillins). While able to resist the activity of β-lactamase, however, these agents are not as effective against Staphylococcus as the natural penicillins, and they are associated with an increased risk for liver toxicity. Moreover, some strains of Staphylococcus have become resistant to penicillinase-resistant penicillins; an example is methicillin-resistant Staphylococcus aureus (MRSA).

Penicillins are used in the treatment of throat infections, meningitis, syphilis, and various other infections. The chief side effects of penicillin are hypersensitivity reactions, including skin rash, hives, swelling, and anaphylaxis, or allergic shock. The more serious reactions are uncommon. Milder symptoms may be treated with corticosteroids but usually are prevented by switching to alternative antibiotics. Anaphylactic shock, which can occur in previously sensitized individuals within seconds or minutes, may require immediate administration of epinephrine.

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The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Adam Augustyn.

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