Virulence and antimicrobial resistance in clinical Enterococcus faecium

Abstract

The aim of the present study was to determine the occurrence of seven virulence determinants in Enterococcus faecium clinical blood culture isolates over a 6-year period and to investigate possible correlations between virulence and antibiotic resistance. Two hundred and sixty-three isolates were screened for the presence of genes coding for aggregation substance ( asa1), cytolysin ( cylA), collagen-binding protein ( ace), Enterococcus faecalis endocarditis antigen ( efaA fs), enterococcal surface protein ( esp fm), gelatinase ( gelE) and hyaluronidase ( hyl fm) by polymerase chain reaction. The minimum inhibitory concentrations (MICs) of ampicillin, ciprofloxacin, gentamicin, imipenem, linezolid and vancomycin were determined by the agar dilution method and the MIC of daptomycin was determined by Etest. The esp fm gene was found in 56% of the isolates, hyl fm in 4%, whilst the other virulence genes were detected only sporadically (≤1%). The level of antibiotic resistance was 77% to ampicillin, 90% to ciprofloxacin and 83% to imipenem; 5% of the isolates were resistant to vancomycin and 2% were resistant to gentamicin (high-level resistance, MIC ≥500 mg/L). A significant correlation was found between the presence of esp fm and resistance to ampicillin, ciprofloxacin and imipenem ( P < 0.01). Twelve isolates were esp fm-positive and ampicillin-susceptible.