Type: Term Pronunciation: ak′tin-ō-mī′sinz Definitions: 1. A group of peptide antibiotic agents, isolated from several species of Streptomyces (originally Actinomyces), which are active against gram-positive bacteria, fungi, and neoplasms. Actinomycins are chromopeptides, most containing the chromophore actinocin, and are deri...