ANTIBIOTICS are, strictly speaking, natural products secreted by microorganisms into their environment, where they inhibit the growth of competing microorganisms of different species. In common usage, the term is generally applied to a wide range of chemicals, whether directly isolated from mould ferments, their semisynthetic derivatives, or synthetic chemicals showing some structural similarities. Also, in everyday language the term is used to denote drugs with a selectively toxic action on bacteria or similar non-nucleated single-celled microorganisms (including chlamydia, rickettsia and mycoplasma), though such drugs have no effect on viruses. In this loose parlance even the sulphonamides may, incorrectly, be referred to as antibiotics because they are antimicrobial. More confusing is the fact that a number of antibiotics are used as cytotoxic agents in cancer chemotherapy (e.g. bleomycin): see ANTICANCER AGENTS. Further, partly because of the recent development of high-throughput screens for lead chemicals, a number of new drug chemical classes have arisen from antibiotic leads (e.g. the CCK antagonist asperlicin and derivatives, from Aspergillus spp.). The antimicrobial antibiotics have a selectively toxic Read more […]