Abstract
The aim of this study is to describe the drug resistance and virulence of enterococci in river water sampled downstream (DRW) and upstream (URW) from the wastewater discharge point, to determine the pool of virulent and drug-resistant enterococci in untreated wastewater (UWW) and the extent to which these bacteria are eliminated from hospital wastewater (HWW) and municipal wastewater treated (TWW) by biological and mechanical methods in a wastewater treatment plant (WWTP). A total of 283 strains were identified with the use of culture-dependent methods and PCR, including seven different species including E. faecalis and E. faecium which were predominant in all analyzed samples. Majority of the strains were classified as multidrug resistant (MDR), mostly on streptomycin and trimethoprim. Strains isolated from wastewater and DRW harbored van genes conditioning phenotypic resistance to vancomycin, the highest percentage of vancomycin-resistant strains (57.0%), mostly strains harboring vanC1 genes (27.6%), was noted in TWW. More than 65.0% of the isolated strains had different virulence genes, the highest number of isolates were positive for cell wall adhesin efaA and sex pheromones cob, cpd, and ccf which participate in the induction of virulence. Many of the strains isolated from TWW were resistant to a higher number of drugs and were more virulent than those isolated from UWW and HWW. The enterococci isolated from DRW and wastewater were characterized by similar multidrug resistance and virulence profiles, and significant correlations were observed between these groups of isolates. These findings suggest that pathogenic enterococci are released with TWW and can spread in the river, pose a serious epidemiological threat and a risk to public health.
Highlights
Wastewater is treated to reduce pollutant concentrations to environmentally safe levels.various compounds and pathogenic fecal bacteria, including antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs), are evacuated to surface water bodies with treated wastewater [1,2,3]
The results of this study indicate that wastewater treatment plant (WWTP) are significant sources of multidrug resistant (MDR) and virulent enterococci in the environment
The strains isolated from treated wastewater (TWW) samples were characterized by higher levels of antibiotic resistance and virulence than those isolated from untreated wastewater (UWW) and, in many cases, hospital wastewater (HWW) samples
Summary
Various compounds and pathogenic fecal bacteria, including antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs), are evacuated to surface water bodies with treated wastewater [1,2,3]. These micropollutants influence the trophic status, microbiological quality, and epidemiological safety of natural ecosystems. Gram positive enterococci rapidly evolve and spread in the environment These oval-shaped bacteria often occur in pairs or short chains, and they are able to grow in a wide range of temperatures (10 ◦ C to 45 ◦ C), pH of 9.6, and NaCl concentration of up to 6.5% [7,8]
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