Antimicrobial resistance could cause up to 10 million deaths every year.
Both the active and inert ingredients in common herbicides induce antibiotic resistance in human pathogenic bacteria, according to the latest research from New Zealand scientists, published in Microbiology this week. Previous research from the same team found in 2015 that commercial formulations of Roundup (containing glyphosate and inert ingredients) and Kamba (containing 2,4-D, Dicamba, and inert ingredients) caused antibiotic resistance to develop in Salmonella eterica andEscherichia coli, but this new research drills down into what ingredients in these formulations resulted in the effect. Lead author of the study, Jack Heinemann, PhD, University Canterbury’s School of Biological Sciences, explains that ultimately this research indicates that, “The sub-lethal effects of industrially manufactured chemical products should be considered by regulators when deciding whether the products are safe for their intended use,”
Scientists parsed out the effects of individual active and inert ingredients by obtaining pure, technical grade dicamba, 2,4-D, and glyphosate, as well as the inert co-formulants “Tween80” and “CMC,” which are respectively, used to reduce surface tension and regulate the viscosity in a formulated herbicide, though also used as emulsifiers in foods like ice cream and in medicines. The technical grade herbicides were first applied to S. eterica, and then a range of antibiotics including ampicillin (Amp), chloramphenicol (Cam), ciprofloxacin (Cip), kanamycin (Kan) and tetracycline (Tet) were used to treat the bacteria. Inert ingredients were applied to both S.eterica and E. coli and then the same antibiotics were tested. Researchers measured the ability for the bacteria to live in a petri dish when compared to unexposed bacteria, a term called efficiency of plating.
Results show a range of effects, with the herbicides conferring different levels of resistance based on the antibiotic used. 2,4-D, for instance, decreased antibiotic resistance in Salmonella eterica after Cam exposure, but increased it after Kan exposure. The inert ingredients recorded similar outcomes, although on the whole their effect was weaker than the active ingredients. In general, the effects of the active ingredients on antibiotic resistance were similar to results found in the original research with formulated products. However, with this study, very small, and much larger amounts of active ingredient were used, indicating that antibiotic resistance is conferred even below levels reasonably expected to be seen in the environment.