Prevalence and Molecular Characterization of Vancomycin Variable Enterococcus faecium Isolated From Clinical Specimens

Vancomycin variable (VVE) bacteria are phenotypically susceptible to vancomycin, but they harbor the gene. We aimed to ascertain the prevalence of VVE among clinically isolated vancomycin-susceptible (VSE) isolates, as well as elucidate the molecular characteristics of the gene cluster within these isolates. Notably, we investigated the prevalence and structure of the gene cluster of VVE. Between June 2021 and May 2022, we collected consecutive, non-duplicated vancomycin-susceptible (VSE) samples. Real-time PCR was performed to detect the presence of , , and . Overlapping PCR with sequencing and whole-genome sequencing were performed for structural analysis. Sequence types (STs) were determined by multilocus sequence typing. Exposure testing was performed to assess the ability of the isolates to acquire vancomycin resistance. Among 282 VSE isolates tested, 20 isolates (7.1%) were VVE. Among them, 17 isolates had partial deletions in the IS or IS sequences in (N=10), (N=5), or (N=2). All VVE isolates belonged to the CC17 complex and comprised five STs, namely ST17 (40.0%), ST1421 (25.0%), ST80 (25.0%), ST787 (5.0%), and ST981 (5.0%). Most isolates were related to three hospital-associated clones (ST17, ST1421, and ST80). After vancomycin exposure, 18 of the 20 VVEs acquired vancomycin resistance. Considering the high reversion rate, detecting VVE by screening VSE for is critical for appropriate treatment and infection control.