Nocardia, Rhodococcus, Actinomadura, Streptomyces, Gordonia, and Other Aerobic Actinomycetes

Aerobic actinomycetes are a heterogeneous group of different genera. These organisms are classified in this group mainly on the basis of microscopic characteristics. Among the aerobic actinomycetes, the genus found most frequently in humans is Nocardia. The genus Rhodococcus (red-pigmented coccus) includes more than 50 species of Gram-positive, partially acid-fast, coccobacillary, obligately aerobic actinomycetes. The genus Actinomadura contains nearly 80 species, of which Actinomadura madurae, Actinomadura latina, and Actinomadura pelletieri may be associated with human infections. Almost 700 species are included in the genus Streptomyces. Streptomyces somaliensis is the most common species in this genus and is usually found in immunocompromised patients. Gordonia and Tsukamurella spp., which are closely related to Rhodococcus spp., are found in the soil and are considered opportunistic human pathogens.