21
Apr
Glyphosate Weed Killer Tied to Widespread Bacterial and Multidrug Resistance, Elevating Silent Pandemic
(Beyond Pesticides, April 21, 2026) A very alarming link between agricultural glyphosate weed killer use and multidrug antibiotic resistance in nosocomial pathogens—those responsible for hospital-acquired infections—is revealed in a study by researchers from the University of Buenos Aires. Glyphosate is the most widely used pesticide in the world. Understanding the relationship between pesticide use, particularly glyphosate, and antimicrobial resistance (AMR) is of increasing urgency.
Most soybeans grown around the world are genetically engineered to resist glyphosate in order for the crop to survive its heavy application to reduce weeds. Argentina is the third largest producer of soybeans after Brazil and the United States. In Argentina, estimated annual glyphosate use averaged about 36 tons between 2020 and 2023, according to the study authors.
The authors emphasize that understanding the relationship between glyphosate and AMR is, like many others in the current agricultural system, a result of siloing—of assumptions and methods, not of crops. Clinical studies of AMR focus on studying specific pathogenic strains in laboratory cultures, while environmental studies use metagenomics—assessing all the microbial genes in an environment to determine which functions are available for microbes to use, without necessarily determining the presence of, or culturing, particular species. The authors advocate a One Health approach, which, according to the World Health Organization, “recognizes that the health of humans, domestic and wild animals, plants, and the wider environment (including ecosystems) are closely linked and interdependent.”
The researchers isolated 68 microbial strains from wetland sediments not directly exposed to herbicides in Argentina’s Paraná Delta, and selected 35 clinical strains from the university’s collection, 19 of which were nosocomial and multidrug-resistant species. They also included 11 strains from herbicide-impacted soil. They exposed both the environmental microbes and the laboratory specimens to a range of antibiotics and glyphosate and determined which strains were most resistant and what strategies the microbes employed to cope with the exposures.
Resistance to glyphosate was common to both categories of microbes. This is in part because such resistance is a normal feature of evolution. In fact, ironically, a class of “last resort” antibiotics called carbapenems is derived from Streptomyces cattleya, a soil bacterium associated with cattle. The authors cite a study showing that in Pseudomonas aeruginosa, sublethal glyphosate exposure produces resistance to the carbapenem antibiotic imipenem. P. aeruginosa was originally a soil and water bacterium, but most human infections now occur in hospitals, and most strains of P. aeruginosa are resistant to nearly all antibiotics. Some strains of Staphylococcus aureus, another terror in hospitals, have also shown resistance to glyphosate. Thus, there is a direct, if unexplored, connection between glyphosate’s ubiquity and the very serious problem of hospital-acquired, multidrug-resistant infections.
The environmental strains most resistant to glyphosate are closely related to the nosocomial pathogens, the Argentine study found. Glyphosate kills weeds via the shikimate metabolic pathway, which was originally assumed to be confined to plants, but is now known to be common to many microbes as well. The bacterial resistance mechanism most familiar to researchers is an inactivating enzyme some bacteria can embed in the shikimate pathway, but microbes can also use other enzymes, modify glyphosate’s target site within the cell, and eject the herbicide molecules with efflux pumps. The genes encoding efflux pumps are known to increase when microbes are subjected to glyphosate stress, and in this study they were very common in at least eight strains. “Overall, the number of efflux pumps and [inactivating enzyme] genes appeared to be a more critical factor in resistance” than the shikimate pathway, the authors write. This finding adds to the evidence that assumptions by pesticide manufacturers and regulators about how living organisms react to chemicals in the environment must be much more closely investigated, and provides more reason to stop using toxic chemicals altogether.
A second study by Brazilian researchers examines genotoxicity and bacterial resistance to glyphosate in soils of the dryland farming region of Petrolândia. These authors cite research showing that a healthy microbial community contains many species and a mix of those either sensitive to or resistant to glyphosate based on their use of the shikimate pathway. Adding large amounts of glyphosate to a soil community shifts that balance considerably, and there is strong evidence that the human gut microbiome reacts much the same way.
Beyond Pesticides has tracked the science on the problem of glyphosate’s effects on the human microbiome numerous times. For example, a August 15, 2024 Daily News reviewed evidence that victims of Parkinson’s disease have profoundly altered gut microbiomes, and that this changes the prognosis for their disease. A detailed a study in Nature Communications created a map of the network of pesticides, gut microbes, and metabolites; the study found 306 pesticide-bacteria pairings—including glyphosate—where gut microbes significantly shifted their metabolisms, and determined that these changes manifested in mouse brain, liver, intestinal, and lung tissues. For a comprehensive view of glyphosate’s plethora of health-damaging effects, including on the microbiome, see the section on glyphosate in the Gateway on Pesticide Hazards and Safe Pest Management.
In the Petrolândia region, the water content of the soil is of special concern given the dry climate. The Brazilian researchers analyzed the solutes in the soil water of several samples from the region for plant nutrients, contaminants and general soil quality. They isolated 28 bacterial species, including the human pathogens Clostridium difficile, Enterobacter cloacae, Stenotrophomonas maltophilia, and Klebsiella variicola. Five of the isolates were multidrug-resistant, with S. maltophilia resistant to eight antibiotics, the highest of any species.
They also analyzed the soils for levels of several metals, including zinc and chromium. (While zinc is a micronutrient, it has been shown to build up to toxic levels in fertilized soils.) They then exposed Drosophila melanogaster (fruit fly) larvae to the Petrolândia soils to determine whether there were DNA-damaging contaminants present. Those larvae show higher DNA damage compared to controls, with zinc and chromium responsible for most of the damage. The authors note that these results are consistent with other research showing that arsenic, chromium, cobalt, lead and nickel are detectable in 22 different pesticides, including 11 glyphosate formulations. Thus, glyphosate can affect soil microbial balance and soil organism functions directly, but also by introducing other harmful contaminants.
Taken together, this new research from regions where glyphosate is king demonstrates that the herbicide reaches far beyond agricultural fields into urban and suburban areas, risking the health and even survival of human beings in need of urgent medical care.
This trend does not need to be taken to its most extreme before choosing the wiser course, that of making agriculture organic, renewable, sustainable, and truly healthy.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources:
Glyphosate resistance as a potential driver for the dissemination of multidrug-resistant clinical strains
Knecht et al.
Frontiers in Microbiology 2026
https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2026.1740431/full
Emerging Bacterial Resistance and Genotoxicity of Water-Soluble Fractions of Agricultural Soils from the Semiarid Region of Brazil Affected by the Continuous Use of Glyphosate
Silva Souza et al.
Bulletin of Environmental Contamination and Toxicology 2026
https://link.springer.com/article/10.1007/s00128-026-04230-1
Glyphosate and glyphosate-based herbicides (GBHs) induce phenotypic imipenem resistance in Pseudomonas aeruginosa
Hahn et al.
Scientific Reports 2022
https://www.nature.com/articles/s41598-022-23117-9
Pesticide-Induced Gut Microbiota Composition Alterations Linked to Parkinson’s Disease Prognosis
August 15, 2024
https://beyondpesticides.org/dailynewsblog/2024/08/pesticide-induced-gut-microbiota-composition-alterations-and-parkinsons-disease-prognosis/
Study Maps the Gut Microbiome and Adverse Impacts of Pesticide Residues
Beyond Pesticides, June 11, 2025
https://beyondpesticides.org/dailynewsblog/2025/06/study-maps-the-gut-microbiome-and-adverse-impacts-of-pesticide-residues/
