Penicillins (P, PCN or PEN) are a group of antibiotics originally obtained from Penicillium moulds, principally P. chrysogenum and P. rubens. Most penicillins in clinical use are synthesised by P. chrysogenum using deep tank fermentation and then purified. A number of natural penicillins have been discovered, but only two purified compounds are in clinical use: penicillin G (intramuscular or intravenous use) and penicillin V (given by mouth). Penicillins were among the first medications to be effective against many bacterial infections caused by staphylococci and streptococci. They are members of the β-lactam antibiotics. They are still widely used today for different bacterial infections, though many types of bacteria have developed resistance following extensive use. About 10% of people report that they are allergic to penicillin; however, up to 90% of this group may not actually be allergic. Serious allergies only occur in about 0.03%. Research highlights the importance of both doctors and patients discussing recorded penicillin allergies. Those who are allergic to penicillin are most often given cephalosporin C (another β-lactam antibiotic) because there is only 10% crossover in allergy between the penicillins and cephalosporins.Penicillin was discovered in 1928 by Scottish scientist Alexander Fleming as a crude extract of P. rubens. Flemings student Cecil George Paine was the first to successfully use penicillin to treat eye infection (ophthalmia neonatorum) in 1930. The purified compound (penicillin F) was isolated in 1940 by a research team led by Howard Florey and Ernst Boris Chain at the University of Oxford.
Fleming first used the purified penicillin to treat streptococcal meningitis in 1942. For the discovery, Fleming shared the 1945 Nobel Prize in Physiology or Medicine with Florey and Chain. Several semisynthetic penicillins are effective against a broader spectrum of bacteria: these include the antistaphylococcal penicillins, aminopenicillins and the antipseudomonal penicillins. Nomenclature
The term "penicillin" is defined as the natural product of Penicillium mould with antimicrobial activity. It was coined by Alexander Fleming on 7 March 1929 when he discovered the antibacterial property of Penicillium rubens. Fleming explained in his 1929 paper in the British Journal of Experimental Pathology that "to avoid the repetition of the rather cumbersome phrase Mould broth filtrate, the name penicillin will be used." The name thus refers to the scientific name of the mould, as described by Fleming in his Nobel lecture in 1945:I have been frequently asked why I invented the name "Penicillin". I simply followed perfectly orthodox lines and coined a word which explained that the substance penicillin was derived from a plant of the genus Penicillium just as many years ago the word "Digitalin" was invented for a substance derived from the plant Digitalis.In modern usage, the term penicillin is used more broadly to refer to any β-lactam antimicrobial that contains a thiazolidine ring fused to the β-lactam core, and may or may not be a natural product. Like most natural products, penicillin is present in Penicillium moulds as a mixture of active constituents (gentamicin is another example of a natural product that is an ill-defined mixture of active components).