The optrA, cfr(D) and vanA genes are co-located on linear plasmids in linezolid- and vancomycin-resistant enterococcal clinical isolates in Italy.

This article focuses on the characterization of linear plasmids carrying the antibiotic resistance genes optrA, cfr(D), and vanA in three multidrug-resistant (MDR) clinical enterococcal isolates: two Enterococcus faecium strains (868 and 1001) and one Enterococcus faecalis strain (2048). Whole genome sequencing and pulsed-field gel electrophoresis confirmed that these resistance genes are co-localized on linear plasmids, with E. faecalis 2048 representing the first reported case of such linear plasmids in this species. Only E. faecium 868 demonstrated successful transfer of these resistance genes to a recipient strain, likely via transmobilization facilitated by a co-resident conjugative plasmid. The study highlights the potential role of linear plasmids in disseminating resistance to last-resort antibiotics oxazolidinones and glycopeptides among enterococci, underscoring the need for further research into their transfer and replication mechanisms.