When people imagine the front line of antibiotic resistance, they may see a hospital where antibiotics are overprescribed, or a feed lot where cattle are pumped full of these drugs. They probably won’t picture a cornfield. But a new study suggests that crop fields may be an important battleground for fighting antibiotic resistance. And the way we farm will decide who wins.
The new study, published in Proceedings of the National Academy of Sciences, found that high-intensity farming, typical of the U.S. Corn Belt, produced soil microbiomes that were more likely to transmit antibiotic-resistant pathogens to humans, compared to lower-intensity farming methods. In other words, modern farming may contribute to drug-resistant infections, which kill up to 4.7 million people per year, worldwide.
To find out how farming methods affect this risk, researchers compared the soil microbiomes from four widely used farming schemes: high-intensity corn cropping with heavy tilling, synthetic fertilizers, and non-antibiotic biocides to combat pathogenic fungi; two medium-intensity cropping schemes, with reduced biocides and tilling, and use of cow manure to reduce or eliminate synthetic fertilizers; and low-intensity grazing rotated with no-till cover crops, with only intermittent biocides, manure, or synthetic fertilizers.
The team analyzed the microbiomes of soils from these farming schemes, as well as the manure used in the medium-intensity fields. Using metagenomics, they quantified the abundance and diversity of antibiotic resistance genes (ARGs), mobile genetic elements (MGEs) capable of transferring these resistance genes from one species of bacteria to another, and known human pathogens capable of receiving those resistance genes.
It was hardly surprising that the manures used to fertilize crops contained plentiful ARGs and MGEs. But once those manures were spread on fields, most of the bacteria harboring them failed to take hold—out-competed by the diverse microbiomes present in the medium-intensity fields. As a result, ARGs and MGEs were actually less abundant in these medium-intensity soils, compared to soils from high-intensity fields that received no manure at all.
The team estimated the relative risk that a pathogen could acquire an ARG and infect humans. They found the risk of transmission significantly higher for high-intensity compared to medium-intensity fields.
They attribute these results to two factors in the high-intensity fields: lower bacterial diversity, less likely to out-compete bacteria with ARGs, and environmental stress due to synthetic fertilizers, biocides frequently containing copper or other heavy metals, and tilling—potentially favoring bacteria with ARGs and MGEs.
Intensive farming is already known to have plenty of costs—such as high greenhouse emissions from synthetic fertilizers and runoff that pollutes rivers, coastal waters, and lakes. But these new findings suggest that it also has another, unrecognized cost: facilitating the spread of drug-resistant pathogens that could harm humans.
Conversely, the authors write, “soil and crop management practices could be strategically leveraged to limit the onward spread of drug-resistant pathogens.”
Nickodem, et al. “Soil management practices shape the abundance, diversity, and spread of antimicrobial resistance.” Proceedings of the National Academy of Sciences. 2026.
Image: Based on TopMicrobialStock/iStock.com. ©Anthropocene Magazine
