Background: The dissemination of polymyxin resistance represents a significant threat to public health. Materials & methods: Sequence-based typing was performed by 53 mcr-1 Escherichia coli isolate...

Floods seriously threaten public health by promoting the spread of antimicrobial-resistant (AMR) bacteria, particularly in urban areas with poor sanitation. In May 2024, the state of Rio Grande do Sul, Brazil, experienced the most severe flood in its history, affecting over 2.3 million people and resulting in extensive dissemination of sewage, contaminating the environment. This study aimed to investigate the presence of Enterobacteriaceae and clinically relevant carbapenemase genes (bla_KPC and bla_NDM) in floodwaters from Porto Alegre using molecular methods. Seventy-nine water samples were collected during four sampling campaigns conducted between May and June 2024. Samples were obtained from flooded areas and points across Guaíba Lake. DNA was extracted with the DNeasy PowerWater Kit, and qPCR was performed using TaqMan assays targeting Enterobacteriaceae, bla_KPC and bla_NDM. Of the 79 samples, 75 yielded sufficient DNA for analysis. Enterobacteriaceae were detected in 100% of the samples, across all collections. The bla_KPC gene was detected in 100% of the first collection pools, and in 94.7%, 94.7%, and 85.7% of samples from the second, third, and fourth collections, respectively. The bla_NDM gene was present in 81.3% of the first collection pools, and in 78.9%, 89.4%, and 80.9% of samples from the subsequent collections. The high prevalence of Enterobacteriaceae and carbapenemase genes in floodwaters reveals an alarming environmental dissemination of AMR genetic markers. These findings underscore the need for environmental AMR surveillance, especially in disaster settings, and support the implementation of the One Health approach to mitigate the spread of resistance genes across human, animal, and environmental interfaces.