Potential dissemination of multidrug-resistant pathogens into local watersheds via aircraft wastewater from overseas aviation network

Cross-border air travel contributes to antimicrobial resistance (AMR) spread, yet evidence linking aircraft wastewater to local environmental contamination remains limited. Metagenomic sequencing revealed that aircraft wastewater harbors approximately 10-fold higher levels of antibiotic resistance genes (ARGs) compared to municipal wastewater treatment plant (WWTP) influents (∼2.5 ARGs/cell) and effluent-receiving water (∼ 0.35 ARGs/cell). Furthermore, distinct resistome signatures and microbial assembly patterns were identified in aircraft wastewater relative to those in domestic wastewater sources. Notably, throughout this continuum, closely related Escherichia coli strains (ST2, with ≤10 core-genome single-nucleotide polymorphism differences) were isolated from WWTP samples receiving aircraft wastewater, whereas no such isolates were found in non-related samples. These strains consistently exhibited polymyxin resistance (carrying the mcr-1 gene) and extended-spectrum β-lactam (multidrug) resistance, a trait maintained under environmental selection (iCAMP, R² fit = 0.23), as confirmed by fluorescence-based bacterial tracing assays. Source-tracking further revealed that aircraft wastewater from regions with higher microbial community similarity, rather than geological proximity, contributed more substantially to domestic wastewater-borne multidrug resistant genes composition. Our findings suggest a potential route by which multidrug-resistant bacteria and ARGs associated with last-resort antibiotics may disseminate from the overseas aviation network into domestic WWTPs and effluent-receiving water, supporting integrated oversea-to-local surveillance.