antibiotic
n. a drug used to destroy pathogenic or otherwise harmful microorganisms, especially bacteria. Antibiotics can be produced by or obtained from living cells (e.g., molds, yeasts, bacteria) or manufactured as synthetic chemicals with effects similar to natural antibiotics. Some work by interfering with bacterial reproduction, whereas others may disrupt the normal life functions of the pathogen. Antibiotics are ineffective against viruses. Overuse and inappropriate use of these agents are contributing to the development of bacterial resistance to many commonly used antibiotics.