The Actinomycetaceae(often called actinomycetes or mycilial bacteria) comprise a family of bacteria in the order Actinomycetales that contains the medically important genus Actinomyces. This family contains three potentially pathogenic genera: Actinomyces, Nocardia, and Streptomyces. These organisms are closely related to the mycobacteria, but were originally classified as fungi because they were thought to be transition forms between bacteria and fungi.