| Summary: |
This is a multidisciplinary study which integrates three areas of expertise - Microbiology, Analytical Chemistry and Technology of Wastewater Treatment. Although it is consensual that disinfectants, heavy metals and antibiotics are released continuously to the municipal sewage, it is not clear whether the treated wastewater is free of such residues. Moreover, it is also not clear, if the presence of such residues imposes the selection of bacteria resistant to antimicrobial agents. Through an integrated approach, this project aims to bring some insights into these two aspects of the wastewater treatments and wastewater quality. It is proposed to study, to identify and, whenever possible, quantify the influence of chemical, biological, and physical factors responsible for the survival and/or proliferation of antibiotic resistant bacteria during municipal wastewater treatment.
This project was designed based on previous and ongoing studies of our group that, confirming diverse reports of other authors, showed that a well-functioning municipal wastewater treatment, although reducing the microbial charge, does not eliminate antibiotic resistant bacteria, and may contribute to the dissemination of these organisms and/or of their genes. These observations raised some hypotheses that will be addressed during this study, namely: 1) if a similar effect is observed in wastewater treatment plants with different treatment systems; 2) if the observed effect is merely a consequence of the treatment process or if it results from the presence of selective pressure, as antibiotic residues.
Two municipal wastewater treatment plants, one including a trickling filter biological reactor and the other, a submerged fixed-bed bioreactor, will be compared with another one, previously studied, that uses an activated sludge process. To make the comparison more clear, all the parameters will be analysed as ratios of raw influents versus treated effluents. The normalization of these a  |
Summary
This is a multidisciplinary study which integrates three areas of expertise - Microbiology, Analytical Chemistry and Technology of Wastewater Treatment. Although it is consensual that disinfectants, heavy metals and antibiotics are released continuously to the municipal sewage, it is not clear whether the treated wastewater is free of such residues. Moreover, it is also not clear, if the presence of such residues imposes the selection of bacteria resistant to antimicrobial agents. Through an integrated approach, this project aims to bring some insights into these two aspects of the wastewater treatments and wastewater quality. It is proposed to study, to identify and, whenever possible, quantify the influence of chemical, biological, and physical factors responsible for the survival and/or proliferation of antibiotic resistant bacteria during municipal wastewater treatment.
This project was designed based on previous and ongoing studies of our group that, confirming diverse reports of other authors, showed that a well-functioning municipal wastewater treatment, although reducing the microbial charge, does not eliminate antibiotic resistant bacteria, and may contribute to the dissemination of these organisms and/or of their genes. These observations raised some hypotheses that will be addressed during this study, namely: 1) if a similar effect is observed in wastewater treatment plants with different treatment systems; 2) if the observed effect is merely a consequence of the treatment process or if it results from the presence of selective pressure, as antibiotic residues.
Two municipal wastewater treatment plants, one including a trickling filter biological reactor and the other, a submerged fixed-bed bioreactor, will be compared with another one, previously studied, that uses an activated sludge process. To make the comparison more clear, all the parameters will be analysed as ratios of raw influents versus treated effluents. The normalization of these analyses will be made based on the comparison of treatment efficacy assessed through standard parameters (BOD; COD; total heterotrophs, faecal coliforms, enterococci). Other chemical parameters to analyse include the content of heavy metals (e. g. Hg, Pb, As, Zn, Cd, Cr), of antibiotic residues (e.g. quinolones, beta-lactams, tetracyclines, sulfonamides, amynoglycosides, macrolides) and of disinfectants (e.g. triclosan, quaternary ammonium compounds). The antibiotic resistance patterns and prevalence in the raw influent and in the treated wastewater will be analysed phenotypically in isolates of enterobacteria, pseudomonads and other non-fermenting Proteobacteria, enterococci and staphylococci. Also the diversity of the microbiota of the raw influent and of the treated effluent will be compared using a culture independent method PCR-DGGE.
The phenotypic characterization of the antibiotic resistance patterns and relative percentages will be correlated with the chemical analyses in order to detect and, whenever possible, quantify the selective pressure factors responsible for the maintenance of antibiotic resistant bacteria in the treated wastewater. Besides the clonal selection, also horizontal gene transfer may contribute to the high rates of antibiotic resistant bacteria found in municipal wastewater. Through the isolation and characterization of genetic elements related with such recombination processes it will be assessed the relevance of horizontal gene transfer in each wastewater treatment facility. |