Nocardiosis and Actinomycosis

Nocardia species are strictly aerobic, gram-positive, branching, filamentous rods which are beaded appearing and stained variably with the modified acid-fast Kinyoun stain. They can fragment into pleomorphic, rod-shaped, or coccoid pieces. Nocardia are sometimes difficult to recognize and identify in the laboratory, leading to delays in clinical diagnosis. Their relatively slow growth can result in the cultures being discarded before the colonies can be seen. Nocardia are found most often in the environment in soil, water, and vegetation. More than half of the time, these organisms are opportunistic pathogens, causing disease in both solid organ and stem cell transplantations. Less recognized as opportunistic pathogens are Actinomyces species, gram-positive, anaerobic bacilli which are not acid-fast. These organisms are morphologically similar to Nocardia species and can be confused on Gram staining. Nocardia and Actinomycetes cause distinct syndromes which will be reviewed here.