Impact of glyphosate herbicides on prevalence of antimicrobial resistance in soils

Antimicrobial resistance (AMR) currently represents one of the most serious health-related problems. To unveil the mechanisms that affect AMR in the environment is crucial because environmental bacterial communities are the source of antibiotic resistance genes subsequently detected in the clinic. Biocides that are not used as antimicrobial agents but have an antimicrobial activity can exert a selective pressure towards more resistant bacterial strains. This is often overlooked in risk assessment of the use of such compounds. Glyphosate inhibits the Shikimate pathway, which is necessary for the synthesis of aromatic amino acids in plants but also in bacteria. Therefore, glyphosate could exert a selective pressure on bacteria, favouring tolerant/resistant strains in the environment. Because one microorganism can carry several AMR genes (ARG), our working hypothesis is that the intensive use of glyphosate herbicides is a relevant driving factor for the development and spread of AMR in the environment. We have isolated bacteria from the sediment of the Parana river in Argentina and tested them for their tolerance towards glyphosate as neat compound and glyphosate-containing herbicide, and antibiotics. Our results indicate that glyphosate can favour the prevalence of species of bacteria that are naturally multidrug resistant, or bacteria that are active in the acquisition of ARG from clinical sources. The first objective of this proposal is to investigate the genotypic reasons of the phenotypical observations by whole genome sequencing of the isolated strains. Furthermore, we propose to take samples from a soya field to quantify indicator genes for AMR and mobile genetic elements (MGE) through qPCR in order to compare our results with quantitative data from other studies. Any progress in understanding the mechanisms of the interrelationship between herbicide resistance and AMR, as well as the epidemiology of AMR related to herbicide use, is fundamental to develop guidelines for the rational use of herbicides.