Antibiotics, toxic metals and multiresistant bacteria in hospital and urban sewage and their potential impact on receiving water ecosystems

Abstract

Hospital and urban sewage are considered as matrices that pose risks to human and environmental health due to the microbiological composition of pathogens and chemical substances. Among the chemical pollutants are antibiotics and toxic metals because they are considered pollutants of the environment and selectors of multiresistant bacteria due to their antibacterial characteristics. Therefore, hospital and WWTP sewages are considered reservoirs of resistant microorganisms, favoring the exchange of genetic elements of resistance, as well as facilitating their environmental dissemination. In these matrices, clinically important bacteria bearing antibiotic resistance genes was identified, representing a risk due to the limited therapeutic options available. Some metals such as Ag, As, Cd, Cu, Hg, Te, and Zn have antibacterial properties and interest as antimicrobials has been reemerging with increasing bacterial resistance to antibiotics around the world. However, mechanisms of resistance to these metals are already being described mainly in coexistence with antibiotic resistance genes, but their epidemiological distribution is not known. Such pollutants can adversely impact receiving water ecosystems and pose risks to users if they are not removed at sewage treatment plants. In this sense, the objectives of the present study are to quantify antibiotics and toxic metals and to verify the occurrence of multiresistant bacteria (carriers of resistance genes) in hospital sewage, in urban raw and treated sewage and in rivers and to evaluate the possible impacts on the water ecosystems receptors and the risks to the adjacent population. In the tertiary hospital, samples will be collected from three sewage inspection boxes that intercept effluents from outpatient clinics, infirmaries and the confluence of all hospital effluents. At the treatment plant, samples will be collected in the inlet (raw sewage) and after the secondary settler (treated sewage), prior to launching into the stream. The dosages of cefotaxime, ceftazidime, imipenem, meropenem, ciprofloxacin, gentamicin, sulfamethoxazole and tetracycline will be determined by HPLC and the toxic metals Ag, As, Cd, Cu, Hg, Te and Zn by ICP-MS. The bacterial identification will be through isolation in selective culture media and biochemical kits. The antibiotic sensitivity test will be performed by disc-diffusion in agar and the disc tests combined with clavulanic acid and Blue Carba will be used to identify bacteria producing spectral-extended ²-lactamases and carbapenemases, respectively. Genes from antibiotic hydrolyzing enzymes as well as resistance to toxic metals will be screened for PCR and sequencing. Next, the transferability of mobile genetic elements of resistance through conjugation experiments will be evaluated. The data will be evaluated in statistical programs and according to the evidence will be made a reflection on the possible impacts on the water ecosystems receiving effluents with the chemical and microbiological pollutants studied. (AU)