Role of membrane vesicles in the transmission of vancomycin resistance in Enterococcus faecium.

Clonal transmission and horizontal gene transfer (HGT) contribute to the spread of vancomycin-resistant enterococci (VRE) in global healthcare. Our study investigated vesiduction, a HGT mechanism via membrane vesicles (MVs), for vanA and vanB genes that determine vancomycin resistance. We isolated MVs for VRE of different sequence types (STs) and analysed them by nanoparticle tracking analysis. Selected MV samples were subjected to DNA sequence analysis. In resistance transfer experiments, vancomycin-susceptible enterococci were exposed to MVs and bacterial supernatants of VRE. Compared to bacteria grown in lysogeny broth (MVs/LB), cultivation under vancomycin stress (MVs/VAN) resulted in increased particle concentrations of up to 139-fold (ST80). As a key finding, we could show that VRE isolates of ST80 and ST117 produced remarkably more vesicles at subinhibitory antibiotic concentrations (approx. 9.2 × 10 particles/ml for ST80 and 2.4 × 10 particles/ml for ST117) than enterococci of other STs (range between 1.8 × 10 and 5.3 × 10 particles/ml). In those MV samples, the respective resistance genes vanA and vanB were completely verifiable using sequence analysis. Nevertheless, no vancomycin resistance transfer via MVs to vancomycin-susceptible Enterococcus faecium was phenotypically detectable. However, our results outline the potential of future research on ST-specific MV properties, promising new insights into VRE mechanisms.