Phenotypic detection and molecular characterization of vancomycin-resistant enterococci

Abstract

Background: The emergence of resistance among enterococci threatens to make vancomycin obsolete in the treatment of infections caused by these bacteria. Resistance is observed most commonly in Enterococcus faecium, which is often resistant to aminoglycosides and β-lactams and to a lesser extent in other Enterococcus species, including Enterococcus faecalis. Aim: The aim of this study is to estimate the prevalence of vancomycin-resistant enterococci and study types of glycopeptide resistance genes. Materials and Methods: A total of 100 nonrepeat isolates of enterococci from various clinical samples were analyzed. As per the Clinical and Laboratory Standards Institute guidelines enterococci were screened for vancomycin resistance by Kirby–Bauer disc diffusion method. The minimum inhibitory concentration of all isolates for vancomycin was determined by Epsilometer test. Multiplex polymerase chain reaction (PCR) was carried out for vancomycin-resistance enterococcal isolates using six sets of primers to identify van genes responsible for resistance. Results: Twelve percent isolates were found to be vancomycin resistant. By multiplex PCR 100% vancomycin-resistant isolates carried vanA gene. However, vanB, vanC, vanD, vanE, vanG genes which encode other resistance ligase were not detected. Amplicons were sent for sequencing and the sequence received showed 100% identity with vanA gene. Conclusion: The prevalence of vancomycin resistance among enterococci isolates in this study was 12%. Multiplex PCR can detect van genes with high sensitivity and specificity responsible for vancomycin resistance. Treating serious infections caused by vancomycin-resistant enterococci has emerged as one of the leading clinical challenges for physicians because of limited therapeutic options.