Weedkillers Linked to Antimicrobial Resistance Spread, Study Finds
Each year, antimicrobial resistance (AMR) causes an estimated 1.1 to 1.4 million deaths globally. Research now indicates that AMR spread can be driven by weedkillers, not solely by bacterial evolution against antibiotics. This revelation highlights a new, concerning factor in the global health crisis.
Startling Study Findings
Dr. Daniela Centrón, a researcher at the Institute of Medical Microbiology and Parasitology in Buenos Aires and senior author of a study published in Frontiers in Microbiology, reported a critical discovery. Common multidrug-resistant hospital bacteria are not only resistant to multiple antibiotic classes but also to high concentrations of the widely used weedkiller, glyphosate. These findings suggest that agricultural weedkillers may unintentionally select for AMR within soil bacterial communities, thereby contributing to the spread of resistance.
"Common multidrug-resistant hospital bacteria are resistant to both multiple antibiotic classes and high concentrations of the weedkiller glyphosate." - Dr. Daniela Centrón
Methodology and Key Results
Between 2018 and 2020, Centrón and her colleagues meticulously collected 68 bacterial strains from sediments in the Paraná delta. This wetland area is located near agricultural regions where glyphosate is frequently applied. The strains were then tested for their resistance to 16 common antibiotics, as well as to pure glyphosate and various glyphosate-based herbicides.
The results from these environmental strains were compared with 19 multidrug-resistant strains obtained from local hospitals and 15 strains from feedlots and herbicide-impacted agricultural soils.
Key observations included:
- Hospital strains demonstrated resistance to 1 to 16 of the tested antibiotics, with a concerning 74% resistant to carbapenems.
- Crucially, all hospital strains also exhibited high resistance to glyphosate and glyphosate-based weedkillers.
- Dr. Camila Knecht noted that if these highly resistant bacteria enter the environment via untreated hospital wastewater, they could readily thrive in glyphosate-used agricultural areas, accelerating their spread.
- Even strains from the Paraná delta, an area without direct glyphosate application, displayed at least partial resistance to the chemical.
- Enterobacter strains proved remarkably resilient, tolerating the highest glyphosate concentrations (up to 80 mg/mL), while Bacillus strains were susceptible at much lower concentrations (2.5 mg/mL).
- High glyphosate resistance was also consistently found in hospital infection strains categorized with extreme drug resistance.
Bacterial Relatedness and Environmental Spread
A comprehensive phylogenetic analysis was conducted on all 102 bacterial strains. This analysis revealed a significant pattern: those bacteria most resistant to glyphosate were often closely related, irrespective of whether they originated from hospitals, agricultural areas, or the Paraná delta. The same bacterial genera demonstrated glyphosate resistance across all environments studied.
Dr. Jochen A Müller from Karlsruhe Institute of Technology, a co-author, summarized the interconnected nature of this problem:
"Glyphosate use in the environment leads to resistant bacteria in soils, while antibiotic use fosters resistance in hospitals. Bacteria carrying antibiotic resistance genes can spread between these environments in both directions, with the water cycle being a key transmission factor."
Urgent Policy Recommendations
The use of glyphosate is already a subject of global controversy, having been linked to harm in arthropods such as bees and classified as a probable human carcinogen by the International Agency for Research on Cancer. This has led several countries, including France, Belgium, the Netherlands, and Germany, to implement restrictions on its use.
In light of these new findings, Dr. Centrón has put forward crucial policy recommendations:
- Policies for pesticide use should mandate co-selection testing with antibiotics before new products are marketed.
- Product labels ought to include clear warnings that antibiotic resistance genes can potentially spread from glyphosate-contaminated soils to hospitals via untreated water sources.