Bacteria that masquerade as fungi: actinomycosis/nocardia.

The order Actinomycetales includes phylogenetically diverse but morphologically similar aerobic and anaerobic bacteria that exhibit filamentous branching structures which fragment into bacillary or coccoid forms. The aerobic actinomyces are a large, diverse group of gram-positive bacteria including Nocardia, Gordona, Tsukamurella, Streptomyces, Rhodococcus, Streptomycetes, Mycobacteria, and Corynebacteria. The anaerobic genera of medical importance include Actinomyces, Arachnia, Rothia, and Bifidobacterium. Both Actinomyces and Nocardia cause similar clinical syndromes involving the lung, bone and joint, soft tissue, and the central nervous system. The medically important Actinomyces organisms cause infections characterized by chronic progression, abscess formation with fistulous tracts and draining sinuses. Called "great masqueraders," diagnosis of actinomycosis and nocardiosis is often delayed. Once recognized, treatment of these infections requires long courses of parenteral and oral therapy. This review will compare and contrast infections due to Actinomyces and Nocardia.