Antibiotics | Occurrence and Risk Assessment of Antibiotic Residues and Resistant Bacteria in Treated Sewage Effluents

This study represents the first integrated application of chemical quantitative analysis, phenotypic profiling of resistant bacteria, and ecological risk modeling in South America to systematically evaluate environmental risks of antibiotics and resistant bacteria in wastewater treatment plant discharges. It highlights limitations of conventional treatment processes in removing antibiotics and resistant bacteria, and advocates for incorporating resistance monitoring into wastewater discharge standards, providing a replicable framework for AMR surveillance in tropical urban water systems.

 

Literature Overview
This article titled 'Occurrence and Risk Assessment of Antimicrobials and Resistant Bacteria in Treated Sewage Effluents in South Brazil' published in the journal Antibiotics reviews ecological risks associated with antibiotic residues and resistant bacteria in urban wastewater discharges. The study employs LC-MS/MS to quantify 13 antibiotic concentrations, phenotypic profiling to identify resistant bacterial species, and combines ecotoxicological experiments with risk modeling to assess potential impacts on aquatic ecosystems. The findings provide novel evidence regarding wastewater treatment plants' roles in antimicrobial resistance (AMR) propagation.

Background Knowledge
Antimicrobial resistance (AMR) has emerged as a global public health and environmental security crisis. While wastewater treatment plants (WWTPs) serve as centralized systems for urban wastewater treatment, their limited removal efficiency for antibiotics and resistant bacteria means treated effluents may still contain active residues. These residues pose not only toxicological risks to non-target organisms but also promote AMR dissemination through selective pressure. This study focusing on southern Brazil's WWTPs systematically evaluates co-occurring risks of antibiotic residues and resistant bacteria using multidimensional analysis. It further demonstrates that conventional culture-dependent methods may underestimate resistance diversity, recommending modern techniques like metagenomics and qPCR for comprehensive AMR dynamics characterization.

 

 

Research Methods and Experiments
The study conducted five-month monitoring at a major wastewater treatment plant in Curitiba, southern Brazil. LC-MS/MS quantified 13 common antibiotics while phenotypic profiling identified resistant bacterial species. Ecotoxicological assessment employed bioassays with the green algae Desmodesmus subspicatus. Risk evaluation combined single-substance and mixture toxicity models, with resistance selective pressure modeling using log-normal distributions.

Key Conclusions and Perspectives

• All 13 antibiotics were consistently detected over five months with total concentrations ranging 1730–2840 ng L−1, dominated by carbapenems (24.7%), aminoglycosides (22.2%), and tetracyclines (19.6%).
• Resistant bacteria including Escherichia coli, Klebsiella spp., and Alcaligenes spp. demonstrated resistance to high-concern antibiotics (e.g., fluoroquinolones, carbapenems).
• Single-antibiotic ecological risk quotients (HQecotox) remained <1, but mixture toxicity assessment revealed acute and chronic toxicity affecting 49% and 57% of aquatic species respectively, indicating potential ecological impacts from mixed exposures.
• Resistance selective pressure modeling showed all antibiotics exceeded the risk threshold (HQres.sel. >1), with MER (5601), CIP (2033), AMX (1043), and ENR (1019) exhibiting most significant resistance risks.
• Multivariate analysis identified strong correlations between fluoroquinolones/macrolides and resistant bacteria detection, while other antibiotic classes showed no clear concentration-resistance associations.

Research Significance and Prospects
This study underscores wastewater treatment plants as critical monitoring nodes for AMR, advocating for resistance indicators in discharge regulations. It demonstrates conventional treatment processes' inadequacy in mitigating antibiotic and resistant bacteria risks, recommending advanced treatments like ozonation, activated carbon adsorption, or constructed wetlands. Future research should integrate molecular detection with metagenomic analysis to comprehensively characterize resistance transmission pathways. The study provides a methodological framework for AMR monitoring in tropical urban water systems and supports regional AMR surveillance network development.

 

 

Conclusion
This study systematically reveals wastewater treatment plants' environmental impacts regarding antibiotic residues and resistant bacteria propagation, demonstrating risks to ecosystems and public health even when physicochemical parameters meet standards. It recommends regulatory bodies incorporate resistance selective pressure modeling alongside traditional ecotoxicity indicators in discharge criteria. Through multidimensional analysis, the research delivers empirical data on AMR propagation in tropical urban wastewater systems, supporting development of advanced treatment technologies to reduce environmental antibiotic and resistance burdens. Cyagen Biosciences offers animal models and cell models services to advance AMR mechanism studies and novel therapeutic strategies.

 

Keite da Silva Nogueira, Ana Paula de Oliveira Tomaz, Gabrielly Cristina Kubis, Bárbara Zanicotti Leite, and Marcelo Pedrosa Gomes. Occurrence and Risk Assessment of Antimicrobials and Resistant Bacteria in Treated Sewage Effluents in South Brazil. Antibiotics.