Molecular detection of virulence factors and antibiotic resistance pattern in clinical Enterococcus faecalis strains in Sardinia

Abstract

In this study, the antibiotic resistance pattern and the presence of genes encoding several virulence factors in 91 Enterococcus faecalis strains isolated from different human clinical sources in Sardinia were investigated. Genotypic determination of virulence genes (gelE, esp, agg, ace, cylA,B,M,L(L),L(S), efaA, fsrB) was carried out by PCR. The production of gelatinase and haemolytic activity were also determined. Antimicrobial susceptibility tests were performed by an automated microdilution test (Vitek). The strains examined in this study contained at least one and up to as many as all virulence genes investigated. Examining the distribution of these factors in the different groups of clinical strains, we found that all but one virulence determinant were detected more frequently among urinary isolates. The detection of some factors by PCR did not always correlate with its phenotypic expression. Antibiotic susceptibilities among the Enterococcus faecalis strains investigated in our study were typical for the species, with expected levels of acquired resistance. Faecal isolates had the highest percentage of resistance, especially to high level-gentamicin, ciprofloxacin and norfloxacin. In summary, a wide variety of genes encoding virulence factors have been detected among our clinical Enterococcus faecalis strains, and those isolated from UTI were characterized by a higher virulence potency compared with strains from other clinical sources. Silent virulence genes (cyl or gelE) were frequently detected, therefore both the genotypic and phenotypic assays seem necessary for a better characterization of the strains. Our results may serve as a basis for additional surveillance studies of infections caused by this microorganism.