Abundance and diversity of airborne antibiotic resistome and mobilome in Belgrade metropolitan area during summer season: a metagenomic approach

Introduction: The importance of the environment for the transmission of antimicrobial resistance is increasingly acknowledged. The airborne transmission route of antibiotic resistance genes (ARGs) is particularly significant since ARGs-carrying bioaerosols could travel long distances and remain in the atmosphere for a long period of time. In addition, mobile genetic elements (MGEs) can promote the spread of ARGs in the environment. Objective: To reveal the potential of the atmosphere in the dissemination of ARGs and MGEs, the antibiotic resistome and mobilome of airborne metagenomes collected during summer season 2024 at seven locations in the Belgrade metropolitan area were analysed. Method: Outdoor air was sampled at seven locations using hydrophobic polypropylene membrane filters (air volume of 30 m3). Airborne DNA samples were subjected to shotgun metagenome sequencing (Illumina Novaseq X plus) and bioinformatic analysis (Novogene, UK). ARGs and MGEs were annotated using CARD, Integrall, Isfinder and Plasmid databases, respectively. Findings: The tested locations were selected according to the air pollution during heating season (highly polluted: Borca, Despota Stefana, Lestane, Zemun Ugrinovacka, Veliki Crljeni; low polluted: Barajevo, Zeleno brdo). Metagenomic analysis revealed that the air sampled at Zemun Ugrinovacka showed the highest abundance of ARGs, while the lowest level was observed in sample Barajevo. The most abundant ARG was blaTEM, while transposon TnSwi1 was dominant in four samples. MGEs content profiles varied among the samples, although Veliki Crljeni and Lestane showed similar patterns of MGEs relative abundance. Conclusion: This study revealed that Belgrade air could be a potential dissemination route for antimicrobial resistance.