Sulfonamide resistance as a global one health challenge.

Sulfonamide resistance is often viewed as a consequence of antibiotic misuse; however, growing evidence reveals its widespread distribution across humans, animals, and the environment. Escherichia coli exhibits sulfamethoxazole resistance of 44-57%, with 93% of isolates carrying sul1 or sul2, while sul4 has recently emerged in companion animals; many resistant strains harbor class 1 integrons linking sulfonamide resistance to other antibiotics. Although constructed wetlands remove 86-99% of sulfamethoxazole from wastewater, sul1 frequently persists ( ~ 10⁵ copies/mL), and in aquaculture, milkfish exposed to sulfamethoxazole (2 mg/L for 8 weeks) showed resistance increasing from 2.8% to 100% with survival reduced by up to 62%. These findings underscore sulfonamide resistance as an ecological challenge maintained across interconnected reservoirs, imposing a One Health approach to disrupt its transmission.