Emergence of resistance to macrolides and rifampicin in clinical isolates of Rhodococcus equi from foals in central Kentucky, USA: 1995 to 2017 [Epidemiology and Surveillance]

Objective: To determine the prevalence of R. equi strains resistant to macrolides and rifampicin over time in clinical samples from foals submitted to diagnostic laboratories in central Kentucky.

Methods: Retrospective observational study of all clinical samples from foals that were submitted to veterinary diagnostics laboratories in Kentucky between January 1995 and December 2017. Samples were included if R. equi was cultured and tested for in vitro susceptibility to erythromycin or rifampicin.

Results: In vitro susceptibility to erythromycin was available for 2169 isolates of R. equi while susceptibility to both erythromycin and rifampicin was available for 1681 isolates. Rifampicin resistance was first detected in 2000 and erythromycin resistance was first detected in 2004. Between 1995 and 2006, the proportion of resistant isolates of R. equi was 0.7% for erythromycin and 2.3% for rifampicin. There was a significant (P <0.001) increase in the proportion of resistant R. equi between 2007 and 2017, with 13.6% of isolates being resistant to erythromycin and 16.1% being resistant to rifampicin. Between 2007 and 2017, isolates of R. equi resistant to erythromycin or rifampicin were significantly less likely to be isolated from feces than from the respiratory tract, other soft tissues, or musculoskeletal infections.

Conclusions: The considerable increase in the prevalence of isolates of R. equi resistant to macrolides and rifampicin since 2007 is of concern for both human and animal health.

https://ift.tt/2CNS4x0