Survey of Virulence Determinants among Vancomycin Resistant Enterococcus faecalis and Enterococcus faecium Isolated from Clinical Specimens of Hospitalized Patients of North west of Iran

Yaeghob Sharifi

doi:10.2174/1874285801206010034

Abstract

Recent data indicates an increasing rate of vancomycin resistance in clinical enterococcal isolates worldwide. The nosocomial enterococci are likely to harbor virulence elements that increase their ability to colonize hospitalized patients. The aim of this study was to characterize virulence determinants in vancomycin-resistant enterococci (VRE) obtained from various clinical sources.During the years 2008 to 2010, a total of 48 VRE isolates were obtained from three University teaching hospitals in Northwest, Iran. Initially, phenotypic speciation was done and minimum inhibitory concentrations (MICs) of vancomycin were determined by agar dilution method and E-test. Then, species identification and resistance genotypes along with detection of virulence genes (asa1, esp, gelE, ace and cpd) of the isolates were performed by multiplex PCR.Thirty eight isolates were identified as vancomycin-resistant Enterococcus faecium (VREfm) and ten as E. faecalis (VREfs). Irrespective of the species, vanA gene (89.58%) was dominant and three phenotypically vancomycin susceptible E. faecium isolates carried the vanB gene. Among virulence genes investigated, the esp was found in 27(71%) VREfm strains, but did not in any VREfs. Other virulence determinants were highly detected in VREfs strains. Our data indicate a high prevalence of E. faecium harboring vancomycin resistance with vanA genotype and the two VRE species displayed different virulence genes.

Highlights

Enterococci are Gram-positive intestinal commensals of humans and other animals, in addition to be an isolate from environmental sources
Our data indicate a high prevalence of E. faecium harboring vancomycin resistance with vanA genotype and the two vancomycin-resistant enterococci (VRE) species displayed different virulence genes
Most of VREs were isolated from intensive care units (ICUs) [16(33.3%)], nephrology [10(20.8%)] and internal [8(16.7%)] wards

Summary

Introduction

Enterococci are Gram-positive intestinal commensals of humans and other animals, in addition to be an isolate from environmental sources. During the past decades an enhancement in the prevalence of enterococal infections such as bacteremia and urinary tract infections along with emergence of multi antimicrobial resistance, VRE has been reported worldwide [1, 2]. Among vancomycin-resistance phenotypes in enterococci, VanA and VanB possess highest clinical importance. Strains resistant to vancomycin and teicoplanin were assigned to. VanA phenotype while, those susceptible to teicoplanin but resistant to vancomycin were considered as the VanB phenotype [2]. The vanA and vanB gene clusters contain nine different genes for a two-component regulatory system (vanR and vanS), three resistance genes (vanH, encoding dehydrogenase; vanA or vanB, encoding ligase; vanX, encoding DD-dipeptidase); an accessory gene (vanY); and the vanZ gene, which is present in the vanA gene cluster whereas, the vanW gene is found only in the vanB operon. VanA is carried on Tn1546 whilst, VanB on transposons Tn1547 and Tn1549, which may be found on plasmids or inserted on the chromosome [3]

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