Selection for Resistance to a Glyphosate-Containing Herbicide in Salmonella enterica Does Not Result in a Sustained Activation of the Tolerance Response or Increased Cross-Tolerance and Cross-Resistance to Clinically Important Antibiotics

Abstract

Evolution of bacterial tolerance to antimicrobials precedes evolution of resistance and may result in cross-tolerance, cross-resistance or collateral sensitivity to other antibiotics. Transient exposure of gut bacteria to glyphosate, the world's most widely used herbicide, has been linked to the activation of the stress response and changes in susceptibility to antibiotics. In this study, we investigated whether a chronic exposure to a glyphosate-containing herbicide (GBH) results in resistance, a constitutive activation of the tolerance and stress response and cross-tolerance or cross-resistance to antibiotics. Of the ten farm animals-derived clinical isolates of Salmonella enterica subjected to experimental evolution in increasing concentrations of GBH, three isolates showed a stable resistance with mutations associated with the glyphosate target gene aroA and no fitness costs. The global quantitative proteomics analysis demonstrated activation of the cellular tolerance and stress response during the transient exposure to GBH, but not constitutively in the resistant mutants. Resistant mutants displayed no cross-resistance or cross-tolerance to antibiotics. These results suggest that while transient exposure to GBH triggers cellular tolerance response in Salmonella enterica, this response does not become genetically fixed after selection for resistance to GBH and does not result in increased cross-tolerance or cross-resistance to clinically important antibiotics under our experimental conditions. Importance Glyphosate-based herbicides (GBH) are among the world's most popular, with traces commonly found in food, feed and the environment. Such high ubiquity means that the herbicide may come into contact with various microorganisms, on which it acts as an antimicrobial and may select for resistance and cross-resistance to clinically important antibiotics. It is therefore important to estimate whether the widespread use of pesticides may be an underappreciated source of antibiotic resistant microorganisms that may compromise efficiency of antibiotic treatments in humans and animals.

Glyphosate and glyphosate-based herbicides (GBHs) induce phenotypic imipenem resistance in Pseudomonas aeruginosa

“…At the same time, MRIS is due to the over-expression of the mexAB-oprM efflux operon in clinical P. aeruginosa strains, while strains harbouring plasmid-mediated carbapenemase genes usually belong to the type III (IRMR) group 61 . In our study, we have discovered phenotypic imipenem resistance in parallel with meropenem and doripenem susceptibility in both clinical and environmental P. aeruginosa strains after co-exposure to antibiotics and GBHs, therefore, we presume, that the detected changes can be related to the porin regulation of oprD as it was described in the case of IRMS type strains 61 or to other general mechanisms against stressors 60 . The molecular mechanisms of the glyphosate and GBH-induced imipenem resistance in P. aeruginosa are yet to be investigated.…”

“…The nonheritable resistance to antibiotics in E. coli induced by salicylates and other chemotactic repellents 59 , the kanamycin resistance of E. coli in the presence of GLY 26 and the kanamycin/ciprofloxacin resistance of S. Typhimurium induced by the exposure to Roundup 26 were previously reported. The imipenem resistance of P. aeruginosa induced by GLY and GBHs has a similar pattern and rapidity: therefore, it may be activated by an efflux or permeability-related mechanism as it was suggested in the case of E. coli 26 , or by the activation of general mechanisms against potential stressors, which does not necessarily require a change in the specifically targeted structures 60 .…”

Indirect Effects of the Herbicide Glyphosate on Plant, Animal and Human Health Through its Effects on Microbial Communities

“…A potential connection between glyphosate exposure, populations of pks + bacterial species such as E. coli and intestinal cancer development needs to be investigated (Davoren and Schiestle, 2018). Connections between glyphosate resistance in bacteria and antibiotic resistance also deserve more attention (Kurenbach et al, 2015;Kurenbach et al, 2018;Pöppe et al, 2020). As suggested by us earlier (van Bruggen et al, 2018), independent and trustworthy research is needed to revisit the tolerance thresholds for glyphosate residues in water, food and animal feed taking all possible health risks into account.…”

“…and other environmental bacteria (Kurenbach et al, 2015;Kurenbach et al, 2018;van Bruggen et al, 2018;Wicaksono et al, 2021). Other glyphosate resistance mechanisms have not been associated with antibiotic resistance (Pöppe et al, 2020).…”

Unveiling the Impact of Antibiotics and Alternative Methods for Animal Husbandry: A Review

“…Data from the World Health Organization showed that some of the common resistant bacteria include Escherichia coli, Klebsiella pneumoniae , Salmonella spp., Streptococcus pneumoniae and Staphylococcus aureus are, in fact, common pathogens of both humans and livestock [ 55 ]. The situation is further complicated by the fact that resistance against a particular antibiotic group can offer cross-resistance to another antibiotic group [ 56 , 57 ]. Today, infections with antibiotic-resistant microorganisms lead to significant healthcare and economic losses, and are associated with extended hospital stays, higher mortality rates and greater risk of complications [ 58 , 59 , 60 ].…”