The novel and transferable erm (51) gene confers macrolides, lincosamides and streptogramins B ( MLS B ) resistance to clonal Rhodococcus equi in the environment

Abstract

Summary The use of mass antimicrobial treatment has been linked to the emergence of antimicrobial resistance in human and animal pathogens. Using whole‐genome single‐molecule real‐time (SMRT) sequencing, we characterized genomic variability of multidrug‐resistant Rhodococcus equi isolated from soil samples from 100 farms endemic for R . equi infections in Kentucky. We discovered the novel erm (51)‐encoding resistance to MLS B in R . equi isolates from soil of horse‐breeding farms. Erm (51) is inserted in a transposon (Tn Erm 51) that is associated with a putative conjugative plasmid (pRErm51), a mobilizable plasmid (pMobErm51), or both enabling horizontal gene transfer to susceptible organisms and conferring high levels of resistance against MLS B in vitro. This new resistant genotype also carries a previously unidentified rpoB mutation conferring resistance to rifampicin. Isolates carrying both vapA and erm (51) were rarely found, indicating either a recent acquisition of erm (51) and/or impaired survival when isolates carry both genes. Isolates carrying erm (51) are closely related genetically and were likely selected by antimicrobial exposure in the environment.

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