Penicillin (sometimes abbreviated PCN) refers to a group of β-lactam antibiotics used in the treatment of bacterial infections caused by susceptible, usually Gram-positive, organisms. The name “penicillin” can also be used in reference to a specific member of the penicillin group. Penicillins have the molecular formula R-C9H11N2O4S, where R is a variable side chain.
History
The serendipitous discovery of penicillin is usually attributed to Scottish scientist Alexander Fleming in 1928, though others had earlier noted the antibacterial effects of Penicillium. Fleming noticed a halo of inhibition of bacterial growth around a contaminant blue-green mould on a Staphylococcus plate culture. Fleming concluded that the mould was releasing a substance that was inhibiting bacterial growth and lysing the bacteria. He grew a pure culture of the mould and discovered that it was a Penicillium mould, now known to be Penicillium chrysogenum. Fleming coined the term "penicillin" to describe the filtrate of a broth culture of the Penicillium mould. Even in these early stages, penicillin was found to be most effective against Gram-positive bacteria, and ineffective against Gram-negative organisms and fungi. He expressed initial optimism that penicillin would be a useful disinfectant, being highly potent with minimal toxicity compared to antiseptics of the day, but particularly noted its laboratory value in the isolation of "Bacillus influenzae" (now Haemophilus influenzae).Fleming A. On the antibacterial action of cultures of a penicillium, with special reference to their use in the isolation of B. influenzæ. Br J Exp Pathol 1929;10(31):226–36. After further experiments, Fleming was convinced that penicillin could not last long enough in the human body to kill pathogenic bacteria and stopped studying penicillin after 1931, but restarted some clinical trials in 1934 and continued to try to get someone to purify it until 1940.