Effect of Macrolide and Rifampin Resistance on the Fitness of Rhodococcus equi

This work advances our understanding of the opportunistic environmental pathogenRhodococcus equi , a disease agent affecting horses and immunocompromised people.R. equi is one of the most common causes of severe pneumonia in young horses. For decades, the standard treatment forR. equi pneumonia in horses has been dual antimicrobial therapy with a macrolide and rifampin; effective alternatives to this combination are lacking. The World Health Organization classifies these antimicrobial agents as critically important for human medicine. Widespread macrolide and rifampin resistance inR. equi isolates is a major emerging problem for the horse-breeding industry and might also adversely impact human health if resistant strains infect people or transfer resistance mechanisms to other pathogens. This study details the impact of antimicrobial resistance onR. equi fitness, a vital step for understanding the ecology and epidemiology of resistantR. equi isolates, and will support development of novel strategies to combat antimicrobial resistance.