This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists analyzed the genomes of gut microorganisms from an extensive population of 875 wild house mice (Mus musculus) collected from farms in Germany. They searched for genes responsible for resistance to common antibiotics and correlated the presence of these ARGs in the mice with a range of environmental and host variables, such as land use and farming practices, livestock density for cattle, pigs and poultry, sex and physical condition of the mice, as well as climatic variables.
The findings are published in the journal Nature Communications. These statistical analyses aimed to explain the influence these factors have on which and how many ARGs are present in the mice's gut microbiome. In a second step, they compared the resistance profiles in the mice's genomes with resistance genes found in the manure of farm animals, whose genomic data are publicly available from other projects.
Previous studies have shown that water bodies in urban areas and agricultural land are heavily contaminated with antibiotic-resistant bacteria. The scientists therefore expected that antibiotic resistance would also be detected in wild animals in the immediate vicinity of large livestock farms. "We had no idea of the extent to which the transfer of resistance genes might be detected in wild animals," says Dr.
Víctor Hugo Jarquín-Díaz of the Max Delbrück Center. "We expected some overlap, but we were surprised to find that around 50% of the resistance genes from cattle, pigs and chickens were also present in our wild mice." This shows that there are many ecological bridges between humans, farm animals and wildlife, and that spatial proximity can imply functional, ecological interdependence—and, in the case of antibiotic-resistant bacteria, indeed does. Furthermore, the scientists found that environmental variables and the intensity of livestock farming have a greater influence on the specific resistance profile in the gut microbiome of a wild farm mouse than the mouse's own characteristics.
The way agricultural land in the immediate vicinity of the farm is used, and the resulting direct and indirect contact with farm animals, explains three times as much about which ARGs are detectable in the mouse as the mouse's sex or body condition. "Our statistical models showed that certain factors have a very strong effect on the presence of specific resistance genes," says Professor Emanuel Heitlinger, who conducted this study at Humboldt-Universität zu Berlin and the Leibniz-IZW and is now associated with the Federal State Agency for Consumer & Health Protection Rhineland-Palatinate. "For example, pig farming density is strongly associated with resistance genes related to antibiotics that are widely used in veterinary and farming practices, such as sulfonamides, tetracyclines or beta-lactams." There are therefore direct, demonstrable effects of intensive livestock farming on specific forms of antibiotic resistance in wildlife.
According to the team of authors, ecological concepts have so far been insufficiently integrated into microbiome research. The study highlights highly relevant links between hosts, microbiomes, resistance genes and spatial environmental factors. "We were able to identify pathways of resistance extending beyond the boundaries of medical or agricultural systems into the environment," says Professor Stephanie Kramer-Schadt, head of department at the Leibniz-IZW and professor at Technische Universität Berlin.
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