Antimicrobial Resistance in Rhodococcus equi.

Pneumonia caused by Rhodococcus equi remains an important cause of disease and death in foals. The combination of a macrolide (erythromycin, azithromycin, or clarithromycin) with rifampin has been the recommended treatment for foals with clinical signs of infection caused by R. equi since the early 1980s with, until recently, only rare reports of resistance. Resistance to macrolides and rifampin in isolates of R. equi cultured from horses is increasing, with isolates resistant to all macrolides and rifampin now being cultured from up to 40% of infected foals at some farms. This text reviews the available data regarding antimicrobial resistance in R. equi, with emphasis on the molecular mechanisms of the recent emergence of resistance to macrolides and rifampin in equine isolates of R. equi.