Overwintering waterbirds are important reservoirs for the spread of antibiotic resistance genes (ARGs): Shared patterns at the waterbird-environment interface and the risk of horizontal transfer

The global spread of antibiotic resistance genes (ARGs) has become a critical challenge to public health. Long-distance migratory waterbirds are recognized as important biological vectors in the transregional spread of ARGs. However, the sharing patterns of ARGs and the horizontal transfer risks between these birds and their habitats during the wintering period remain poorly understood. This limits a comprehensive understanding of their role in ARG transmission. This study investigated a typical wintering wetland in southwestern China along the East Asian–Australasian Flyway, using metagenomic approaches to systematically characterize the distribution patterns, sharing profiles, and horizontal transfer risks of ARGs in the guts of overwintering waterbirds and their associated aquatic and terrestrial habitats. The results show that multidrug resistance genes are the predominant type of resistance observed both in the guts of overwintering waterbirds and in their habitats. Extensive sharing of ARGs occurs between the guts of overwintering waterbirds and their habitats, with approximately 50% of the 1,250 identified ARG subtypes shared by both. We detected 55 high-risk ARG subtypes belonging to 10 resistance categories. Among these, β-lactam resistance genes (e.g., blaNDM-5 and blaCTX-M-15 ) were the predominant types. In addition, the co-localization of ARGs with mobile genetic elements (MGEs) (e.g., transposons and plasmids) suggests that the gut of waterbirds and aquatic environments may represent potential hotspots for horizontal transfer of ARGs. This study highlights the high connectivity of ARGs between overwintering waterbirds and their habitats, offering important insights into ecological and public health risks related to ARG spread. • Multidrug resistance genes predominate in both waterbirds' guts and their habitats. • Extensive sharing of ARGs occurs between the waterbirds' guts and their habitat. • Waterbirds' guts exhibit higher abundance and greater diversity of high-risk ARGs. • Waterbirds' guts and aquatic environments are high-risk areas for the HGT of ARGs. • Various pathogenic bacteria carrying ARGs are present and pose a risk of HGT.