vancomycin vănˌkōmīˈsĭn [key], antibiotic resembling penicillin in the way it acts. It is derived from the bacterium Streptomyces orientalis, which was isolated from soil of India and Indonesia. Vancomycin destroys Gram-positive bacteria, especially staphylococci and enterococci (see Gram's stain). It seems to function by inhibiting the formation of the bacterial cell wall, as does penicillin; it may also cause damage to the cell membrane. The drug is intensely irritating to tissues and is usually used only for infections where microorganisms are resistant to penicillin (see drug resistance). Vancomycin must be administered intravenously because it is not absorbed through the gastrointestinal tract. Mutant microorganisms resistant to vancomycin are rare.

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