Effect of a glyphosate-containing herbicide on Escherichia coli and Salmonella ser. Typhimurium in an in vitro rumen simulation system

Abstract

Glyphosate (N-(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 Escherichia coli or Salmonella serovar Typhimurium are higher when glyphosate residues are present in the feed, an in vitro fermentation trial with a “Rumen Simulation System” (RUSITEC) and a glyphosate-containing commercial formulation was performed.Colony forming units of E. coli and Salmonella ser. Typhimurium decreased steadily in all fermenters, regardless of the herbicide application. Minimum inhibitory concentrations of the studied Salmonella and E. coli 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 E. coli and Salmonella strain in the in vitro fermentation system, nor promoted resistance to glyphosate or antibiotics.

No hints at glyphosate-induced ruminal dysbiosis in cows

“…When summarizing the results of the analyses of rumen microbial products, the composition of the ruminal microbiome, the associations of rumen microbial taxa with feed and microbial products and finally the detection of fecal pathogenic Clostridia it becomes obvious, that the principal diet composition unsurprisingly had a strong impact on the ruminal microbiome and its fermentation products, while glyphosate apparently had no relevant effects. This is in agreement with in vitro observations using mixed cultures of microorganisms from ruminal fluid showing that glyphosate had no adverse effects on simulated ruminal microbiomes 29 , 30 . The absence of long-term glyphosate effects in the gastrointestinal tract is not surprising, since excess of amino acids is available and synthesis of aromatic amino acids can possibly be bypassed through transport 19 .…”

Effects of Different Formulations of Glyphosate on Rumen Microbial Metabolism and Bacterial Community Composition in the Rumen Simulation Technique System

“…The RUSITEC system, which was used here, is a more complex system, which is able to maintain the core bacterial community of the rumen over a longer time (Wetzels et al, 2018). Our results agree with previous RUSITEC studies, which observed only minor effects of glyphosate on the rumen bacterial population and no effects on the growth of pathogenic bacteria (Riede et al, 2016;Bote et al, 2019). In a recent in vivo study with dairy cattle, Billenkamp et al (2021) observed differences for only four taxa, which, however, appeared to be linked closer to experimental conditions than to glyphosate application.…”

“…High glyphosate levels (10 mg/l) did also not affect establishment of Escherichia coli or Salmonella Ser. Typhimurium in the RUSITEC system (Bote et al, 2019). Schnabel et al (2017) did not observe adverse effects of a glyphosate-contaminated diet (intake up to 84.5 mg/d) on performance or energy balance of dairy cows, neither did this affect leucocytes or erythrocytes (Schnabel et al, 2020) or the rumen microbiome (Billenkamp et al, 2021).…”

Does Glyphosate Affect the Human Microbiota?

“…Pathogens tend to have superior stress responses due to their higher adaptiveness under stress conditions; for example, the transition from the environment into their host [ 46 , 47 ]. Thus, glyphosate as a stress factor may reduce bacterial susceptibility, either as a stress response or via mutations and change the bacterial response to antibiotics [ 12 , 49 , 50 , 51 , 52 , 53 ]. In turn, the heavy use of antibiotics and other chemicals may lead to bacterial co- and cross-resistance to glyphosate and other antimicrobials [ 8 , 46 , 54 ].…”