+49 30 838 51845
Background and objectives: Glyphosate is currently the most widely used herbicide in the world. Glyphosate acts on enolpyruvylshikimate-3-phosphate synthase (EPSPS), which is also present in bacteria. Concerns have been raised about the potential effects of glyphosate in animal feed on bacteria in farm animals. Here, we investigated the current levels of resistance to glyphosate (as an active ingredient and as a part of a complete herbicide formulation) in diverse isolates of Escherichia coli and Salmonella spp.
Materials and methods: We determined minimal inhibitory concentrations (MIC) of glyphosate and Roundup LB plus in Müller-Hinton I medium using a broth microdilution method for 120 Salmonella spp. and 238 E. coli isolates.
Results: The distribution of MIC values for Salmonella spp. was 40-80 mg/ml for both glyphosate and Roundup, and 5-10 mg/ml for glyphosate and 20-40 mg/ml for formulation for E. coli. Among the isolates with a MIC higher than the 95%-percentile the pathogenic E.coli were the dominant subgroup. Phylogenetic relationship, antibiotic resistance profile and geographical location of sample isolation did not have a large effect on glyphosate sensitivity in both species. Whereas, as well as host animal species and time point of isolation seem to have some slight effects on glyphosate MIC.
Conclusion: These results demonstrate that although Salmonella spp are more resistant to glyphosate than E. coli, the MIC distribution within the species is small, suggesting the absence of a highly resistant subpopulation in farm animal-associated Enterobacteriaceae.