rif·a·my·cin .rif-ə-'mīs-ən n any of several antibiotics that are derived from a bacterium of the genus Streptomyces (S. mediterranei)
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rif·a·my·cin (rif″ə-miґsin) any of a family of antibiotics biosynthesized by a strain of Amycolatopsis rifamycinica, effective against a broad spectrum of bacteria, including gram-positive cocci, some gram-negative bacilli, and Mycobacterium tuberculosis and certain other mycobacteria. The five components are designated A, B, C, D, and E; rifamycins O, S, and SV are derivatives of the B component, and AG and X are derivatives of the O component. In the United States the rifamycins are used only for the initial treatment and retreatment of pulmonary tuberculosis and for prophylaxis of meningococcal infections in close contacts of patients with Neisseria meningitidis infection; they have been used in other countries to treat various infectious diseases due to susceptible organisms, such as leprosy, gonorrhea, and biliary tract and respiratory infections.Medical dictionary. 2011.