Rhodococcus equi pneumonia.

Corynebacterium equi is a pleomorphic gram-positive rod that was first isolated in 1923 by Magnusson, and is the cause of suppurative broncho-pneumonia in foals. The organism, now know as Rhodococcus equi, is ubiquitous in nature and is increasingly recognized as pathogenic, particularly in the immunocompromised population. Cavitary pneumonia clinically resembling Mycobacterium tuberculosis is the most common manifestation of R equi disease, but extrapulmonary infections are seen as well. Long term treatment with intracellularly active antimicrobial agents is required.