Assessment of Tetracycline Resistant Escherichia coli in Chlorine and UV Disinfected Effluents and Surface Waters

<div class="line" id="line-5"> <b> Background: </b> Wastewater treatment plants (WWTP) have been one of the sources of antibiotic resistant bacteria in surface waters. Tetracycline is a major antibiotic commonly used in human and veterinary medicine. The purpose of this study was to compare the removal of tetracycline resistant <i> Escherichia coli </i> in wastewater treatment plants (WWTP) utilizing chlorine and UV disinfection and the occurrence of these bacteria in surface water used for recreational purposes.</div><div class="line" id="line-10"> <br/></div><div class="line" id="line-12"> <b> Methods: </b> Samples were collected from six WWTP (three with UV and three with chlorine disinfection) from influent, secondary treated and disinfected effluents; upstream and downstream rivers and beaches. Sample collection was repeated at each WWTP five times. Serial dilutions from 101 to 106 were prepared for influents and secondary effluents by using sterile phosphate saline water. Triplicates of diluted influents, secondary, and undiluted disinfected effluents and surface waters were filtered (100 ml each) through a sterile membrane filtration system using 0.45 &micro;m sterile filters. Tetracycline resistance bacteria (TRB) were enumerated by culturing these filters on mI Agar plates with tetracycline (final concentration 16&micro;g/L) at 37&mp; 0.5℃ for 24 hrs. A control set of filters were also incubated on media without tetracycline at the same conditions, and TRB resistance was calculated as percentages.</div><div class="line" id="line-15"> <br/></div><div class="line" id="line-17"> <b> Results: </b> TRB were present in the influent with an average of 5% of the <i> E. coli </i> population at the WWTP with chlorine disinfection. The presence of TRB significantly increased during secondary treatment (20%) and disinfection decreased TRB presence to 15% in the effluent. TRB resistance also increased significantly (p&lt;0.001) during secondary treatment in WWTP with UV disinfection. The percentage of TRB in the influent dropped from 13% to only 12% after UV disinfection. The occurrence of TRB in surface water varied significantly within locations from 5% to 14%. The highest mean concentrations of TRB were detected at the river with a 20% exceedance of water quality standards for recreational activities.</div><div class="line" id="line-22"> <br/></div><div class="line" id="line-24"> <b> Conclusion: </b> TRB were removed at varying rates depending on the disinfection method and gained resistance during treatment processes. Effluents from WWTP contribute to antibiotic resistance in surface waters. Swimmers at great risk as antibiotic resistant <i> E. coli </i> may cause urinary tract infections among swimmers.</div>