Vancomycin-resistant enterococci in healthcare settings: clonal analysis, resistance profiles, and biofilm formation of strains isolated from hospitalized patients.

Multidrug-resistant bacteria, including vancomycin-resistant Enterococci (VRE), are a significant public health threat. This study aimed to perform molecular characterization of E. faecium and E. faecalis isolates with respect to glycopeptide and phenotypic resistance, and clonal relatedness. A total of 45 isolates (41 E. faecium, 4 E. faecalis) were obtained from clinical specimens collected at the University Hospital in Kraków, Poland. Isolates were screened on chromogenic media, identified by Matrix-Assisted Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) and tested for antimicrobial susceptibility and the presence of vanA/vanB genes. Biofilm formation was assessed on culture media, and clonal relationships were determined using PFGE. Among the isolates, 86.7% harbored vanA and 13.3% vanB genes. E. faecium remained resistant mainly to ampicillin and teicoplanin, but susceptible to tigecycline and linezolid. E. faecalis showed partial susceptibility to ampicillin, tigecycline and linezolid, but frequent resistance to teicoplanin and reduced susceptibility to imipenem. Biofilm assessment revealed that 88.9% of isolates produced high biofilm levels. PFGE analysis identified several clonal groups among Enterococcus faecium, with clone A being the most prevalent (9 strains). The predominance of clonal strains and their robust biofilm production underscore the dissemination potential of VRE in hospital settings. High levels of antibiotic resistance highlight the limited therapeutic options available. Comprehensive preventive and control measures are essential to mitigate transmission of multidrug-resistant pathogens in healthcare environments. These findings provide recent epidemiological data on VRE circulation and highlight the clinical relevance of a dominant, biofilm-forming clonal lineage in a tertiary-care setting.