Effect of a Glyphosate-Containing Herbicide on and Salmonella Ser. Typhimurium in an In Vitro Rumen Simulation System.

Glyphosate (-(phosphonomethyl)glycine) is the most-used herbicide worldwide. Many studies in the past have shown that residues of the herbicide can be found in many cultivated plants, including those used as livestock feed. Sensitivity to glyphosate varies with bacteria, particularly those residing in the intestine, where microbiota is exposed to glyphosate residues. Therefore, less susceptible pathogenic isolates could have a distinct advantage compared to more sensitive commensal isolates, probably leading to dysbiosis. To determine whether the ruminal growth and survival of pathogenic or serovar Typhimurium are higher when glyphosate residues are present in the feed, an fermentation trial with a "Rumen Simulation System" (RUSITEC) and a glyphosate-containing commercial formulation was performed. Colony forming units of and ser. Typhimurium decreased steadily in all fermenters, regardless of the herbicide application. Minimum inhibitory concentrations of the studied and strains did not change, and antibiotic susceptibility varied only slightly but independent of the glyphosate application. Overall, application of the glyphosate-containing formulation in a worst-case concentration of 10 mg/L neither increased the abundance for the tested and strain in the fermentation system, nor promoted resistance to glyphosate or antibiotics.