In October 2025, the World Health Organization again sounded the alarm on the emergence of multidrug-resistant bacteria in hospitals around the world. Researchers have now found evidence that the use of weedkillers, in particular glyphosate, can drive the evolution of antimicrobial resistance in soil bacteria as a side-effect of developing resistance to the weedkiller itself. They hypothesized that resistant bacteria can be transmitted between hospitals and impacted soils in both directions through wastewater and other environmental pathways.
Each year, antimicrobial resistance (AMR) is responsible for an estimated 1.1 to 1.4 million deaths worldwide. Now, scientists have found evidence that the spread of AMR isn’t always driven by bacteria evolving to resist the antibiotics themselves: rather, certain weedkillers can have the same effect.
“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.”
In 2018 and 2020, Centrón and colleagues collected 68 bacterial strains from sediments in a nature reserve in the Paraná delta, a wetland of international importance located north of Buenos Aires. Glyphosate is frequently applied to nearby agricultural areas.
The scientists here tested each strain’s degree of resistance to 16 common antibiotics, such as ampicillin combined with sulbactam, meropenem, tetracycline, and vancomycin. They also measured the strains’ resistance to pure glyphosate and glyphosate-based herbicides – chosen because they are among the most frequently used herbicides around the world. The scientists compared the results with those from 19 strains, including multidrug-resistant species, sampled from local hospitals. Another 15 strains had been isolated from feedlots and herbicide-impacted agricultural soils in the region.
As expected, the hospital strains were each resistant to between 1 and 16 of the antibiotics tested, confirming widespread AMR. Worryingly, 74% were resistant to carbapenems, broad-spectrum antibiotics commonly used as a treatment of last resort. Importantly, all hospital strains also proved highly resistant to glyphosate and glyphosate-based weedkillers. “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 lead author Dr Camila Knecht.
Strains from the Paraná delta spanned 15 genera, including Acinetobacter, Pseudomonas, Exiguobacterium, and Chryseobacterium. Each had at least partial resistance to glyphosate and glyphosate-based weedkillers, even though these have never been used in the reserve itself. Enterobacter strains tolerated the highest concentrations of glyphosate, up to 80 milligram per milliliter. At the other extreme, Bacillus strains, usually found in soils, were particularly susceptible: their growth was already inhibited at a concentration of 2.5 milligram of glyphosate per milliliterAnd high resistance to glyphosate was also found in strains isolated from hospital infections with extreme drug resistance.
When the scientists made a ‘family tree’ of all 102 bacterial strains, those most resistant against glyphosate tended to be close relatives, irrespective of their location of origin. For example, the same genera were found to be resistant against glyphosate across 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.
Glyphosate, usually sold under the brandname Roundup, is the world’s most widely used herbicide. It is known to harm bees, and the International Agency for Research on Cancer has classified it as a probable human carcinogen. France, Belgium, and the Netherlands have banned glyphosate for household use, while Germany currently 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 warming that genes for antibiotic resistance can spread from glyphosate-contaminated soils to hospitals through untreated water,” Centrón counseled.
[This post includes material provided by Frontiers.]
It would have been useful for the article to have specified equally effective alternatives to glyphosate. Looked at strictly logically, any pesticide/herbicide etc. that is effective must be highly toxic. Humanity began its arms race against the natural world when it took up agriculture ten thousand years ago. Anything we grow for food is targeted by other living things who want to eat it. Preventing them doing so will always be difficult and dangerous, and constantly changing.