Antimicrobial Resistance Profiles of Escherichia coli Isolates from Water Samples of Hydroelectric Reservoirs in the Paraná River Basin, Brazil

The spread of antimicrobial-resistant bacteria in aquatic environments is a public health concern, especially in areas with anthropogenic activity. Hydroelectric reservoirs may act as interfaces facilitating the dissemination of resistance. Escherichia coli is used as an indicator of environmental contamination and antimicrobial resistance. 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. 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. Among the investigated resistance markers, ampC was the most frequently detected gene, whereas blaCTX-M was the predominant ESBL-associated determinant. Significant associations were observed between blaCTX-M and resistance to cefotaxime, ceftazidime, and cefepime, whereas the presence of ampC was significantly associated with cefoxitin resistance. Significant associations were observed between β-lactam resistance and ESBL genes. 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.