Glyphosate Co-Selects Multidrug Resistance in 100% of Tested Hospital Strains from Argentina

Researchers at the Institute of Medical Microbiology and Parasitology collected 68 environmental strains from herbicide-free Paraná delta sediment, 15 from glyphosate-exposed feedlot soils, and 19 clinical isolates. Each underwent MIC testing against 16 antibiotics plus pure glyphosate and commercial formulations up to 80 mg/ml, revealing universal glyphosate tolerance in hospital strains and variable tolerance among environmental genera such as Enterobacter and Acinetobacter.

The pattern indicates co-selection: bacteria already carrying multiple resistance mechanisms survive glyphosate levels typical of agricultural runoff. This extends prior observations from European and North American soil studies showing elevated minimum inhibitory concentrations after repeated herbicide application, suggesting the Argentine wetland results reflect regional gene flow from intensive soy and maize production rather than local exposure.

Main limitation is the cross-sectional design without longitudinal sampling or controlled microcosm experiments; plasmid transfer rates under glyphosate gradients remain unquantified. Whole-genome sequencing of resistant isolates plus a multi-year soil surveillance cohort exceeding 500 samples would strengthen causal inference.

Regulatory agencies should require AMR endpoint data in new herbicide registrations when environmental concentrations exceed 10 mg/ml.