Migratory birds-one major source of environmental antibiotic resistance around Qinghai Lake, China

Migratory birds are potential transmitters of bacterial antibiotic resistance. However, their role in the environmental dissemination of bacterial antibiotic resistance and the extent of their impact on the environment are not yet clear. Qinghai Lake is one of the most important breeding and stopover ground for the migratory birds along the Central Asian Flyway. Here, we investigated the bacterial antibiotic resistance in the environment and among the migratory birds around the lake. The results of culture-based analysis of bacterial antibiotic resistance, quantitative PCR and metagenomic sequencing indicate that migratory birds are one major source of bacterial antibiotic resistance in the environment around Qinghai Lake. Network analysis reveals the co-occurrence patterns of antibiotic resistance genes (ARGs) and bacterial genera. Genetic co-localization analysis suggests high co-selection potential (with incidence of 35.8%) among different ARGs, but limited linkage (with incidence of only 3.7%) between ARGs and biocide/metal resistance genes (BMRGs). The high genetic linkage between ARGs and mobile genetic elements (MGEs) is still largely confined to the bacterial community in migratory birds (accounting for 96.0% of sequencing reads of MGE-linked ARGs), which indicates limited horizontal transfer of ARGs to the environment. Nevertheless, the antibiotic resistance determinants carried by migratory birds and their specific genetic properties (high co-selection and mobility potential of the ARGs) remind us that the role of migratory birds in the environmental dissemination of bacterial antibiotic resistance deserves more attention.