Scientists have uncovered evidence that one of the world’s most widely used weedkillers may also help dangerous bacteria survive antibiotic treatments.
Each year, antimicrobial resistance (AMR) contributes to an estimated 1.1 million to 1.4 million deaths worldwide. Researchers now say the rise of drug-resistant bacteria may not be driven only by antibiotics. Common weedkillers could also be helping bacteria survive and spread.
“Here we show that the most common species of multidrug-resistant bacteria from hospitals are not only resistant to multiple antibiotic classes but also to high concentrations of the weedkiller glyphosate,” said Dr. Daniela Centrón, a researcher at the Institute of Medical Microbiology and Parasitology in Buenos Aires and the senior author of the study in Frontiers in Microbiology.
“These results suggest that weedkillers—which, unlike antibiotics, are widely applied in agricultural environments—may have the unintended side effect of selecting for AMR among bacterial communities within the soil.”
Scientists Test Environmental and Hospital Bacteria
In 2018 and 2020, Centrón and her team collected 68 bacterial strains from sediment in a protected wetland area in the Paraná Delta north of Buenos Aires. Nearby agricultural land is regularly treated with glyphosate.
Researchers tested how resistant the strains were to 16 commonly used antibiotics, including ampicillin with sulbactam, meropenem, tetracycline, and vancomycin. They also examined resistance to pure glyphosate and glyphosate-based herbicides, which are among the world’s most widely used weedkillers.
The results were compared with 19 bacterial strains taken from local hospitals, including multidrug-resistant species. Another 15 strains came from feedlots and agricultural soils exposed to herbicides.
Hospital Superbugs Show Strong Glyphosate Resistance
The hospital strains showed resistance to between one and 16 antibiotics, confirming widespread antimicrobial resistance. About 74% were resistant to carbapenems, a powerful class of broad-spectrum antibiotics often used as a last-resort treatment. Every hospital strain also showed strong resistance to glyphosate and glyphosate-based herbicides.
“This means that if these bacteria enter the environment through untreated wastewater from hospitals, they could go on to thrive in agricultural areas where glyphosate is used,” said first author Dr Camila Knecht from Dr Centrón’s group.
The Paraná Delta samples included 15 bacterial genera, such as Acinetobacter, Pseudomonas, Exiguobacterium, and Chryseobacterium. All showed at least some resistance to glyphosate and related herbicides, even though those chemicals have never been applied inside the reserve. Enterobacter strains tolerated the highest glyphosate levels, reaching up to 80 milligrams per milliliter (about 2.7 ounces per gallon).
By contrast, Bacillus strains commonly found in soil were highly sensitive. Their growth was inhibited at glyphosate concentrations of just 2.5 milligrams per milliliter (about 0.08 ounces per gallon). Strong glyphosate resistance was also observed in bacteria linked to highly drug-resistant hospital infections.
Glyphosate Resistance Crosses Environmental Boundaries
When researchers created a genetic “family tree” of all 102 bacterial strains, the most glyphosate-resistant strains were often closely related, regardless of where they were found. The same bacterial genera showed resistance in hospitals, agricultural areas, and the Paraná Delta.
“In the environment, the use of glyphosate leads to the evolution of resistant bacteria in impacted soils, whereas the use of antibiotics favors their evolution in hospitals. Bacteria carrying antibiotic resistance genes can spread and breed between those two niches in both directions and in multiple ways, with the water cycle playing a key role in transmission,” concluded coauthor Dr Jochen A. Müller, a group leader at Karlsruhe Institute of Technology.
Glyphosate remains highly controversial. Studies have linked it to harm in arthropods, especially bees, and the International Agency for Research on Cancer classifies it as a probable human carcinogen. France, Belgium, and the Netherlands have banned glyphosate for household use, while Germany prohibits its use in public spaces.
“Policies for the use of any pesticide, as well as its metabolites, should stipulate the requirement for co-selection testing with antibiotics before marketing. Labels should include a warning that genes for antibiotic resistance can spread from glyphosate-contaminated soils to hospitals through untreated water,” counseled Centrón.
Reference: “Glyphosate resistance as a potential driver for the dissemination of multidrug-resistant clinical strains” by Camila A. Knecht, Barbara Prack McCormick, Verónica E. Álvarez, Adrián Gonzales Machuca, Fernanda Buzzola, Julio Fuchs, Pablo Salgado, Josefina Campos, Jochen A. Müller, María Paula Quiroga and Daniela Centrón, 12 January 2026, Frontiers in Microbiology.
DOI: 10.3389/fmicb.2026.1740431
This study was supported by grants ISID/Pfizer 2019 (#56570859) and PUE 2522 from CONICET given to DC and IMPaM, respectively.
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