Antimicrobial Resistance in Wildlife across Switzerland and the Principality of Liechtenstein: Associations with Environmental Factors and Taxonomic Variation

Antimicrobial resistance (AMR) presents a significant challenge to global public health. Addressing this challenge requires a comprehensive One Health approach that integrates efforts in human, veterinary, and environmental domains. Whereas AMR research in medical and veterinary domains is extensive, AMR research in wildlife has received less attention. However, AMR prevalence in the environment, and specifically in wildlife, ultimately affects human life. In a large study conducted in Switzerland and the Principality of Liechtenstein, we collected 410 rectal swab samples from 37 different wildlife species to quantify the prevalence of Escherichia coli (E. coli) and its resistance to 16 antimicrobial drugs, determined through phenotypical antimicrobial susceptibility testing. The study yielded an 81.5% E. coli isolation rate with a considerable 10.8% of isolates resistant to one or more antimicrobial drugs. Notably, 4.5% of the isolates demonstrated multidrug resistance (MDR). Furthermore, we found that E. coli in omnivores exhibited the highest levels of AMR, significantly higher than in carnivores and herbivores. In addition to these dietary associations, we found that the percentage of forested areas surrounding the sampling locations was inversely related to AMR rates, suggesting that environmental conditions play a role in mitigating AMR. This study provides a large-scale quantification of AMR in a broad range of wildlife species and also identifies diverse patterns of AMR in E. coli, highlighting variations associated with both host species and environmental conditions. Our findings emphasize the role of wildlife as potential indicators of environmental contamination with antibiotics and as reservoirs of resistant bacteria.