Seasonal Surveillance of Urban Water Quality in Southern Brazil Reveals Persistent Carbapenem Resistance Genes Despite Compliance with Bacteriological Standards

Quality control of drinking water is essential for safeguarding public health, particularly in densely populated urban environments. Environmental microbiological monitoring can enhance traditional surveillance by providing deeper insights into the dissemination of pathogens and antimicrobial resistance genes in aquatic systems. In this study, we evaluated the quality of wastewater and treated water from two urban water supply systems, representing the southern and northern regions of Porto Alegre, Rio Grande do Sul, Brazil, across four climatic seasons between 2024 and 2025. Fifteen water samples, comprising raw water from Guaíba Lake and treated water from public distribution points, were analyzed. The Water Quality Index was calculated, microbiological indicators were quantified, and carbapenem resistance genes were detected using molecular assays. Most treated water samples complied with bacteriological standards; however, the blaOXA-48-like gene was recurrently identified in both wastewater and treated water. No resistance genes were detected during the summer, while the blaVIM gene appeared exclusively in spring samples. The detection of carbapenem resistance genes in the absence of cultivable coliforms suggests the persistence of extracellular DNA or viable but non-culturable bacteria, underscoring limitations of conventional microbiological monitoring. Integrating classical microbiological methods with molecular assays provides a more comprehensive evaluation of water quality and supports decision-making within a One Health framework.