Aeromonas hydrophila bacteria in a culture. Credit: Stefan Walkowski, CC BY-SA 4.0, via Wikimedia Commons
A common waterborne bacterium found across South Asian rivers, ponds and wastewater systems carries widespread resistance to multiple antibiotics — including drugs of last resort — according to a large genomic study1. The bacterium, Aeromonas, causes diarrhoeal disease in humans and animals, and its infections are often mistaken for cholera because the symptoms are similar.
Scientists from the Wellcome Sanger Institute, the International Centre for Diarrhoeal Disease Research, Bangladesh, and the Postgraduate Institute of Medical Education & Research, India, analysed 1,853 genomes, including 996 newly sequenced isolates from India and Bangladesh, creating one of the most comprehensive population snapshots of the genus to date.
The team identified 162 antimicrobial resistance (AMR) genes, including genes that confer resistance to last-resort antibiotics such as carbapenems and colistin. Genomic comparisons showed little difference between strains isolated from the environment and those causing human infections, suggesting that environmental strains may readily spill over into people. Aquatic reservoirs linked to aquaculture — including farmed fish such as trout and catfish — may play an important role in this transmission.
The researchers also uncovered a potential diagnostic blind spot. In northern India, about 67% of bacterial isolates grown on laboratory media designed to detect the cholera pathogen Vibrio cholerae were actually Aeromonas. This misidentification could distort cholera surveillance in endemic regions.
The findings suggest that Aeromonas has been largely overlooked — both as an emerging pathogen and as an environmental reservoir of antibiotic-resistance genes. Integrating environmental genomics into disease surveillance could help track how resistance genes move between aquatic ecosystems and human populations.
