Penicillins are Beta-lactam antibiotics used in the treatment of bacterial infections caused by susceptible, usually Gram-positive, organisms. The term "penicillin" can also refer to the mixture of substances that are naturally produced. The term Penam is used to describe the core skeleton of a member of a penicillin antibiotic. This skeleton has the molecular formula R-C9H11N2O4S, where R is a variable side chain.
Penicillins are sometimes combined with other ingredients called beta-lactamase inhibitors, which protect the penicillin from bacterial enzymes that may destroy it before it can do its work.
Penicillin was discovered by the Scottish scientist and nobel laureate Alexander Fleming in 1928. He showed that if Penicillium notatum was grown in the appropriate substrate, it would exude a substance with antibiotic properties. Ampicillin and Amoxicillin are the most widely used penicillins.