Understanding Antibiotic Resistance in Rhodococcus equi Isolates from Foals

Foals with Rhodococcus equi (R. equi) are usually treated with a combination of macrolide and rifampin, however, over the past 10 years, resistance to these has increased significantly. In some farms, up to 40 percent of foals may have resistant isolates, and foals with macrolide-resistant isolates are much more likely to die from infection. The cause for antibiotic resistance is unknown. This study will identify the mechanisms by which R. equi isolates have become resistant and evaluate the genetic diversity of macrolide-resistant isolates. In addition, they will determine if macrolide-resistant isolates have a greater ability to cause disease than their macrolide-susceptible counterparts. Macrolide resistance among R. equi isolates is an emerging threat facing horses and this study will provide the first step toward understanding it.