Vancomycin resistant enterococci: from the hospital effluent to the urban wastewater treatment plant

Vancomycin is an important antibiotic to treat serious nosocomial enterococci infections. Human activities, in particular those related with clinical practices performed in hospitals, can potentiate the transfer and selection of clinically-relevant resistant bacteria such as vancomycin resistant enterococci (VRE). Indeed, previous studies demonstrated the occurrence of VRE in urban wastewater treatment plants and related environments (e.g. sewage, rivers). In this study, the occurrence of VRE in a hospital effluent and in the receiving urban wastewater treatment plant was investigated. Vancomycin and ciprofloxacin resistant bacteria occurred in the hospital effluent and in raw municipal inflow at densities of 103 to 102CFUmL-1, being significantly more prevalent in the hospital effluent than in the urban wastewater. Most of the VRE isolated from the hospital effluent belonged to the species Enterococcus faecalis and Enterococcus faecium and presented multidrug-resistance phenotypes to ciprofloxacin, tetracycline, erythromycin, and high-level gentamicin. The same pattern was observed in clinical isolates and in enterococci isolated from the final effluent of the urban wastewater treatment plant. These results show that hospital effluents discharged into urban wastewater treatment plants may be a relevant source of resistance spread to the environment.