Prevalence of multidrug-resistant gram-negative bacteria carrying mcr genes in freshwater aquaculture systems of Southern Odisha, India.

Antimicrobial resistance (AMR) is a growing global health threat, with freshwater fish increasingly recognised as critical reservoirs of multidrug-resistant (MDR) Gram-negative bacteria (GNB). This study investigated the prevalence and antibiotic resistance profiles of GNB isolated from eight edible freshwater fish species collected from ten sites in the Ganjam district of Odisha, India. From 56 initial isolates, eight MDR GNB (14.2%) were identified through biochemical testing followed by 16 S rRNA gene sequencing. Aeromonas veronii was the most prevalent species (62.5%), followed by Proteus faecis and Pseudomonas spp. Antibiotic susceptibility profiling and minimum inhibitory concentration (MIC) determination revealed widespread resistance to ampicillin, kanamycin, ciprofloxacin, and colistin. All A. veronii isolates demonstrated an MDR phenotype, with 100% PCR positivity for the mcr-1 gene. This study represents the first report of mcr-1-harbouring A. veronii from freshwater fish in Odisha and the second documented case of A. veronii carrying mcr-1 in India. These findings identify edible freshwater fish as potential reservoirs of clinically significant MDR pathogens and underscore the urgent need for One Health–based surveillance and strengthened antimicrobial stewardship in aquaculture systems.