موضوع 1
An antibiotic was a substance, produced by one microorganism, which inhibited the growth of other microorganisms. The advent of synthetic methods has, however, resulted in a modification of this definition and an antibiotic now refers to a substance produced by a microorganism, or to a similar substance (produced wholly or partly by chemical synthesis), which in low concentrations inhibits the growth of other microorganisms. Chloramphenicol was an early example. Antimicrobial agents such as sulphonamides and the 4-quinolones, produced solely by synthetic means, are often referred to as antibiotics.