Enterococci in river Ganga surface waters: propensity of species distribution, dissemination of antimicrobial-resistance and virulence-markers among species along landscape

Abstract

Background: Surface waters quality has declined in developing countries due to rapid industrialization and population growth. The microbiological quality of river Ganga, a life-sustaining surface water resource for large population of northern India, is adversely affected by several point and non-point sources of pollution. Further, untreated surface waters are consumed for drinking and various household tasks in India making the public vulnerable to water-borne diseases and outbreaks. Enterococci, the 'indicator' of water quality, correlates best with the incidence of gastrointestinal diseases as well as prevalence of other pathogenic microorganisms. Therefore, this study aims to determine the distribution of species diversity, dissemination of antimicrobial-resistance and virulence-markers in enterococci with respect to rural-urban landscape along river Ganga in northern India.

Results: Enterococci density (chi2: 1900, df: 1; p < 0.0001) increased from up-to-down gradient sites in the landscape. Species diversity exhibit significant (chi2: 100.4, df: 20; p < 0.0001) and progressive distribution of E. faecalis, E. faecium, E. durans and E. hirae down the gradient. Statistically discernible (p: 0.0156 - < 0.0001) background pool of resistance and virulence was observed among different Enterococcus spp. recovered from five sites in the up-to-down gradient landscape. A significant correlation was observed in the distribution of multiple-antimicrobial-resistance (viz., erythromycin-rifampicin-gentamicin-methicillin and vancomycin-gentamicin-streptomycin; rs: 0.9747; p: 0.0083) and multiple-virulence-markers (viz., gelE+esp+; rs: 0.9747; p: 0.0083; gelE+efaA+; rs: 0.8944; p: 0.0417) among different Enterococcus spp.

Conclusion: Our observations show prevalence of multiple-antimicrobial-resistance as well as multiple-virulence traits among different Enterococcus spp. The observed high background pool of resistance and virulence in enterococci in river waters of populous countries has the potential to disseminate more alarming antimicrobial-resistant pathogenic bacteria of same or other lineage in the environment. Therefore, the presence of elevated levels of virulent enterococci with emerging vancomycin resistance in surface waters poses serious health risk in developing countries like India.

Figure 1

Map of study area/sampling sites in the landscape. Inset view simulates the complete 2510 km stretch of river Ganga from Himalaya to Bay of Bengal. Abbreviations: S#1, site 1: Bithoor (most upstream site); S#2, site 2: Bhairon ghat; S#3, site 3: Parmat ghat; S#4, site 4: sattichaura ghat or nana-rao ghat; S#5, site 5: jajmau (most downstream site). Arrows indicate the direction of surface water flow in the up-to-down-gradient fashion in the landscape. Topographic data based upon Survey of India map (adopted from http://www.ttkmaps.com).

Figure 2

Distribution of single/multiple-antimicrobial-resistance in different Enterococcus spp. Abbreviations: A, ampicillin; P, penicillinG; M, methicillin; G, gentamicin; S, streptomycin (aminoglycoside); Va, vancomycin (glycopeptide); Te, teicoplanin; E, erythromycin; R, rifampicin; T, tetracycline; P-M, penicillinG-methicillin; A-P-Ox-M, ampicillin-penicillinG-oxacillin-methicillin (β-lactam); E-R, erythromycin-rifampicin (Macrolide-rifamycin); Va-G-S/Va-S/Va-G (glycopeptide-aminoglycoside); M-G-S/P-G-S (β-lactam-aminoglycoside); Va-M (glycopeptide-β-lactam); T-E-R (tetracycline-macrolide-rifamycin); E-R-Va (macrolide-rifamycin-glycopeptide); E-R-Va-M (macrolide-rifamycin-glycopeptide-β-lactam); E-R-M/E-R-A/E-R-P (macrolide-rifamycin-β-lactam); E-R-G/E-R-S (macrolide-rifamycin-aminoglycoside); E-R-S-M/E-R-G-M (macrolide-rifamycin-aminoglycoside-β-lactam). All antimicrobial combinations derived from aforementioned antimicrobial abbreviations.