Airborne ARGs in Nordic Urban Homes

Antibiotic resistance genes (ARGs) in airborne dust represent an emerging concern for public health, particularly in indoor environments where external environmental pressures may shape their abundance and diversity. This study assessed the temporal and spatial patterns of airborne ARGs in indoor dust across four Nordic cities (Aarhus, Bergen, Reykjavik, and Uppsala) using electrostatic dust collectors (EDCs) at two time points: 2012 and 2022. Shotgun metagenomic sequencing was performed to profile ARGs, while national antibiotic consumption data were obtained from the European Surveillance of Antimicrobial Consumption (ESAC-Net). Outdoor air pollution data (PM2.5 and PM10) were retrieved from the Copernicus Atmosphere Monitoring Service (CAMS) and meteorological parameters were obtained from the NASA POWER database. Beta diversity analysis revealed significant city-specific differences in ARG composition (PERMANOVA, R² = 0.18, p = 0.03), but no consistent temporal shift over the 10-year period. Macrolide, Tetracycline, and Aminoglycoside resistance genes were among the most abundant and persistent classes. Notably, a new resistance gene (Macrolide_85) emerged across all cities in 2022. While overall antibiotic consumption declined, its correlation with ARG abundance increased over time (Spearman's R = 0.37 in 2022 vs. 0.25 in 2012), suggesting the persistence of ARGs despite reduced selective pressure. Several ARG classes were significantly associated with outdoor particulate matter concentrations, and these associations were further modulated by meteorological conditions. For instance, absolute humidity reduced the PM–Polymyxin resistance association, while wind speed enhanced the association between PM and sulfonamide resistance. These findings highlight the complex and context-specific interplay between antibiotic use, air pollution, meteorological parameters, and ARG dynamics in indoor air. Integrating environmental surveillance with antimicrobial resistance monitoring is crucial for assessing ARG transmission risks in built environments, particularly in the context of climate change.