any of various bacteria (order Actinomycetales) with a branching, filamentous structure; esp., any of a family (Actinomycetaceae) of Gram-positive bacteria that are pathogenic to humans and animals
See actinomycete in American Heritage Dictionary 4
noun
Any of various filamentous or rod-shaped, often pathogenic microorganisms of the order Actinomycetales that are found in soil and resemble bacteria and fungi.