1. A genus of aerobic actinomycetes (family Nocardiaceae, order Actinomycetales), higher bacteria, containing weakly acid-fast, slender rods or filaments, frequently swollen and occasionally branched, forming a mycelium. Coccus or bacillary forms are produced by these organisms, which are mainly saprophytic but may be a cause of mycetoma or nocardiosis.
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