Tandem amplification of the vanM gene cluster drives vancomycin resistance in vancomycin-variable enterococci

Abstract

Background Vancomycin-variable enterococci (VVE) are a potential risk factor for vancomycin resistance gene dissemination and clinical treatment failure. vanM has emerged as a new prevalent resistance determinant among clinical enterococci in China. A total of 54 vancomycin-susceptible enterococci (VSE) isolates carrying incomplete vanM gene clusters were isolated in our previous study. Objectives To determine the potential of vanM-carrying VSE to develop vancomycin resistance and investigate the mechanism of alteration of the resistance phenotype. Methods Fifty-four vanM-positive VSE strains were induced in vitro by culturing in increasing concentrations of vancomycin. Genetic changes between three parent VVE strains and their resistant variants were analysed using Illumina and long-read sequencing technologies, quantitative PCR and Southern blot hybridization. Changes in expression level were determined by quantitative RT–PCR. Results Twenty-five of the 54 VSE strains carrying vanM became resistant upon vancomycin exposure. A significant increase in vanM copy number was observed ranging from 5.28 to 127.64 copies per cell in induced resistant VVE strains. The vanM transposon was identified as tandem repeats with IS1216E between them, and occurred in either the plasmid or the chromosome of resistant VVE cells. In addition, an increase in vanM expression was observed after resistance conversion in VVE. Conclusions This study identified tandem amplification of the vanM gene cluster as a new mechanism for vancomycin resistance in VVE strains, offering a competitive advantage for VVE under antibiotic pressure.

Characterization of clinical enterococci isolates, focusing on the vancomycin-resistant enterococci in a tertiary hospital in China: based on the data from 2013 to 2018

“…Additionally, vanM-containing vancomycin-susceptible E. faecium strains might switch to a vancomycin-resistant phenotype during prolonged vancomycin treatment, leading to a failure of vancomycin treatment [15]. Therefore, it may be necessary to strengthen the surveillance for vanM among clinical Enterococcus isolates [30]. More importantly, we also found a co-occurrence of vanA and vanM among a VREM, which has been reported previously [16].…”

Evolutionary Pathways and Trajectories in Antibiotic Resistance

“…For instance, sulfonamide, trimethoprim, and beta-lactam resistance (including resistance to beta-lactam plus beta-lactamase inhibitors) occurs due to increased gene dosage through amplification of antibiotic hydrolytic enzymes, target enzymes, or efflux pumps (284,285). Amplification of the vanM gene cluster (acting in a similar fashion to vanA) in Enterococcus confers glycopeptide resistance (286).…”

Genomic surveillance of vancomycin-resistantEnterococcus faeciumreveals spread of a linear plasmid conferring a nutrient utilization advantage

“…In contrast to the backbone, the set of cargo genes of pELF_USZ was not common in other E. faecium assemblies. A partial version, including the carbohydrate operons and transcriptional regulators (99.28% identity), but lacking the described framing CDSs, was part of one E. faecium plasmid assembly, pSRR24 46 (Supplemental Fig. S11).…”