Aeromonas in South Asia: genomic insights into an environmental pathogen and reservoir of antimicrobial resistance.

Aeromonads are an ecologically versatile group of bacteria that cause infections in aquatic animals and are recognised as emerging human pathogens. Despite this, our understanding of Aeromonas diversity, especially the relationship between clinical and environmental strains, remains limited. Here, we present a genomic analysis of the Aeromonas genus, comprising 1853 genomes, and a detailed comparison of clinical and environmental strains from South Asia, including 996 newly sequenced genomes from Bangladesh and India. Phylogenetic analyses revealed that Aeromonas is a highly diverse genus, with no distinct clade separating clinical and environmental isolates. We identified 28 Aeromonas species and 905 novel sequence types, comprising 72.5% of the genomes. Notably, we show a high incidence of antimicrobial resistance (AMR) genes across all isolates, including against front and last-line antibiotics. Finally, we highlight frequent misidentification of Aeromonas as Vibrio cholerae, which is relevant to cholera-endemic regions where both genera co-exist and are associated with diarrhoeal disease. Our study underscores Aeromonas as an important environmental AMR reservoir and emerging multi-species pathogen capable of spilling over into human populations.