The discovery, made in Oxford, that crude penicillin could cure systemic and life-threatening bacterial infections was followed by attempts to purify penicillin, to determine its structure and then to produce it by total chemical synthesis. The beta-lactam structure of the molecule, first proposed in October 1943, was a source of controversy until 1945. However, no useful chemical synthesis was achieved and fermentation became the commercial source of the antibiotic. In 1953, one of the products of a Cephalosporium sp. from Sardinia was shown to be a new and hydrophilic penicillin (penicillin N). This was contaminated with a substance having the same side-chain but a characteristic absorption spectrum. The latter, cephalosporin C, showed antibacterial activity but was not inactivated by a penicillinase. The determination of its beta-lactam structure and isolation of its nucleus enabled pharmaceutical companies to produce many semisynthetic cephalosporins. A new tripeptide was later found to be an intermediate in the biosynthesis of both penicillin N and cephalosporin C, and this was followed by the complete elucidation of the biosynthetic pathways leading to these compounds and to benzylpenicillin.