Molecular analysis of Vancomycin-resistant Enterococcus isolated from surface and ground water samples

Abstract

Vancomycin Resistant Enterococcus (VRE) has been responsible for numerous outbreaks of serious infections in humans worldwide. Enterococcus faecium and Enterococcus faecalis are the two main species that usually habour high levels of vancomycin resistance determinants, and cause both hospital and community acquired infections in humans. The difficulty in managing infections caused by antibiotic resistant bacteria particularly VREs has resulted in extensive survei llance studies with this pathogen. In addition, the high interest in VRE surveillance studies is also due to the fact that the pathogen is most often isolated from untreated water that is intended for human consumption. The aim of this study was to isolate VREs from ground and surface water as well as to determine their virulence capabilities using phenotypic and genotypic assays. A total of 170 ground and surface water samples collected between August 2015 and April 2016 were analyzed and 81 potential isolates were screened for characteristics of Enterococcus species using biochemical tests, species specific PCR analysis and sequence analysis. Antimicrobial susceptibil ity tests were performed to determine the antibiotic resistance profiles of the isolates particu lar VREs. A total of 56 isolates were confirmed as Enterococcus species through amplification of ddl genes and sequencing data. The distribution of species comprised Enterococcus faecium (38), Enterococcus faeca/is (17) and Enterococcus saccharo/yticus (1 ). Phenotypic characterization by cluster analysis of the isolates using their antibiotic inhibition zone diameter data was used to determine the similarities as well as resolve differences between isolates from the different water sources and/or locations revealed that the isolates derived from these samples have originated from similar progeny. Large proportions (78.6-83%) of isolates were resistant to vancomycin and nalidixic acid. Forty four VREs isolates were detected phenotypically and most of these isolates (56. 8%) were derived from surface water samples. In addition, a large proportion of the isolates (80.4%) were resistant to multiple antibiotics and the MAR phenotype VANNAL- AMP was dominant among these isolates. A total of 17.9 % of the isolates harboured VRE genes. The

vanA and vanB genes were detected in 16% and 3.6% of the isolates respectively and this was most prevalent among E. faeca/is. The presence of virulence factors in VRE isolates was determined. Virulence determinants were detected in 56.8% of the VRE and 4 of the virulence factors (asa1, esp, gel and hy0. A large proportion (79.5%) of the isolates showed great similarities based on the DNA banding patterns. The findings of this study have demonstrated that enterococci from environmental water of South Africa are resistant to multiple antimicrobial agents, some of which are commonly used for treatment. Furthermore, these isolates harbor significant genes coding for virulence factors, which frequently enhance their pathogenic potential. This study also highlights the need for continuous monitoring for virulent VRE strains in water that is intended for human consumption and household activities.