Enterococci, which are commonly found in the environment, cause serious infections despite the absence of well-defined virulence factors and toxins. Knowing the virulence properties of enterococci is important to understand the complex pathogenic structures. In this study, we aimed to investigate the virulence factors (asa1, hyl, cylA, efa, ebp, ace, esp, gelE, sprE, fsrA, fsrB, fsrC genes, gelatinase activity, hemolysin, hydrogen peroxide and biofilm production) and antibiotic resistance of

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... erococcus faecium and Enterococcus faecalis strains isolated from clinical specimens. A total of 110 enterococcus isolates which were accepted as infectious agents were included in the study. The polymerase chain reaction method was used to identify the isolates and to detect virulence genes. Characteristics of hemolysis, biofilm formation, hydrogen peroxide production and gelatinase activity were investigated by phenotypic methods. The antibiotic susceptibility test was performed with VITEK 2 automated system. E.faecalis ATCC 29212 standard strain was used as a quality control in all tests. Of the 110 enterococci isolates included in the study, 61 were identified as E.faecium and 49 as E.faecalis. The efa gene was the most frequently detected virulence gene (92.7%), followed by ace (83.6%), esp (66.4%), ebp (60.0%), cylA (50.9%), hyl (46.4%), asa1 (45.5%), gelE, sprE, fsrC (33.6%), fsrA (12.7%) and fsrB (11.8%). All genes except hyl were higher in E.faecalis isolates and the difference was statistically significant (p<0.05). Twenty-five (51%) E.faecalis and 1 (1.6%) E.faecium isolates had beta-hemolysis and the difference was statistically significant (p= 0.000). Seven (11.5%) E.faecium and 4 (8.2%) E.faecalis isolates formed biofilm, but the difference was not statistically significant (p> 0.05). Two (3.3%) E.faecium and 14 (28.6%) E.faecalis isolates exhibited gelatinase activity and the difference between the two species was statistically significant (p= 0.000). Hydrogen peroxide production was not detected in any of the isolates. The highest resistance rate was determined against ciprofloxacin (70.9%). The resistance to ampicillin was 69.1%, high level streptomycin 65.1%, high level gentamicin 39.4%, vancomycin and teicoplanin 4.5%, and linezolid 1.8%. In conclusion, our data indicated that virulence factors except hyl gene and biofilm production were higher in E.faecalis isolates but E.faecium isolates were more resistant to antibiotics. In order to prevent infection of such virulent or resistant isolates in the hospital setting, infection control measures must be followed. In vivo studies are needed for the better understanding of the virulence of enterococci.