Antibiotic resistant bacteria in urban sewage: role of treatment plants and environmental dispersion

In this work the presence of antibiotic resistant bacteria (ARB) in wastewater and the role of wastewater treatment plants (WWTPs) in the development and spread of antibiotic resistance were studied on Escherichia coli, with reference to three widespread antibiotics (ampicillin, chloramphenicol and tetracycline) and to the urban sewage of Milan area (Italy). The effluent was collected from three WWTPs, differing in the treatment scheme, in several points along the treatment sequence (WWTP influent, biological effluent, final effluent after disinfection). Antibiotic resistance to ampicillin was observed for E. coli, being the influent to the three WWTPs characterized by different contents of ARB. A limited resistance to chloramphenicol was observed, while no resistance was detected for tetracycline. Biological processes acted in modifying the presence of ARB, while the low presence of E. coli in the WWTPs effluent did not allow to compare the different disinfection processes.