Nocardiosis

PATHOGENS

• Member of aerobic actinomycetes group. Grows slowly on media. Appear as branching, beaded filamentous Gram-positive rods.
• Variably acid fast due to presence of intermediate mycolic acids in cell wall, distinguishes from Actinomyces. May produce sulfur granules, especially in mycetomas.
• Ubiquitous in environment. Most infections acquired by inhalation or direct inoculation.
• Many (possibly all) isolates previously identified as "N. asteroides" now known to have been mis-identified based on current lab standards; type strain of N. asteroides does not appear to have been recovered from recent clinical isolates.
• Human pathogens include N. abscessus (former N. asteroides Type I drug susceptibility pattern), N. brevicatena/paucivorans complex (Type II), N. nova complex (III), N. transvalensis complex (IV), N. farcinica (V; more virulent), and N. cyriacigeorgica (VI), as well as N. brasiliensis (more common in tropics and actinomycetoma) and N. pseudobrasiliensis.
• Each species/complex generally has stereotyped antimicrobial susceptibility patterns.