Antimicrobial resistance profiles of Escherichia coli isolates from water samples of hydroelectric reservoirs in the Paraná River basin, Brazil

Background: The spread of antimicrobial-resistant bacteria in aquatic environments is a growing public health concern, especially in areas with intense anthropogenic activity. Hydroelectric reservoirs may act as interfaces facilitating the dissemination of resistance. Escherichia coli is commonly used as an indicator of environmental contamination and antimicrobial resistance.,Objective: To investigate the occurrence of E. coli in reservoirs of the Urubupungá Hydroelectric Complex (Paraná River basin, Brazil) and to characterize antimicrobial resistance profiles and ESBL/AmpC-related genes.,Methods: Water samples were collected during rainy and dry seasons (2022–2024). A total of 200 E. coli isolates were analyzed by broth microdilution (EUCAST). ESBL and AmpC production were phenotypically assessed, and resistance genes (blaCTX-M, blaTEM, blaSHV, and ampC) were detected by PCR.,Results: Overall, 26% of isolates showed resistance to at least one antimicrobial, mainly tetracycline (18%), amoxicillin (15%), and ampicillin (15%). All isolates were susceptible to imipenem, meropenem, and norfloxacin. ESBL-associated genes were more frequent than AmpC, with blaCTX-M as the predominant determinant. Significant associations were observed between β-lactam resistance and ESBL genes.,Conclusion: Hydroelectric reservoirs under anthropogenic influence may serve as environmental reservoirs of antimicrobial-resistant E. coli, particularly ESBL producers. These findings highlight the role of aquatic environments in the dissemination of clinically relevant resistance genes.