Detection of vancomycin-resistant enterococci (VRE) at four U.S. wastewater treatment plants that provide effluent for reuse

Vancomycin-resistant enterococci (VRE), a leading cause of hospital-acquired infections, can occur in wastewater. However, to date, no previous studies have evaluated the occurrence of VRE at wastewater treatment plants (WWTPs) that send their treated effluent to reuse sites. We evaluated the occurrence, concentration, and antimicrobial resistance patterns of VRE at U.S. WWTPs associated with reuse sites. We collected 44 wastewater samples, representing treatment steps from influent to effluent, from two Mid-Atlantic and two Midwest WWTPs between October 2009 and October 2010. Samples were analyzed for total enterococci and VRE using membrane filtration. Isolates were confirmed using biochemical tests and PCR. Antimicrobial susceptibility testing was performed by Sensititre® microbroth dilution. Data were analyzed by two-sample proportion tests and analysis of variance. We detected VRE in 27% (12/44) of all wastewater samples collected and VRE represented 3% of total enterococci detected at all WWTPs. More samples were VRE-positive from the Mid-Atlantic compared to the Midwest WWTPs (p = 0.008). VRE concentrations decreased as treatment progressed at all WWTPs, except at Mid-Atlantic WWTP1 where there was an increase in VRE concentrations in activated sludge reactor samples. VRE were not detected in chlorinated effluent, but were detected in one un-chlorinated effluent sample. All unique VRE isolates were multidrug resistant. Fifty-five percent (12/22) of the isolates displayed high-level aminoglycoside resistance. Our findings show that chlorination reduces the occurrence of VRE in wastewater. However, WWTP workers could be exposed to VRE during wastewater treatment. Our data also raise potential concerns about VRE exposure among individuals who come into contact with un-chlorinated reclaimed water.