Aeromonas Species Diversity, Virulence Characteristics, and Antimicrobial Susceptibility Patterns in Village Freshwater Aquaculture Ponds in North India

Background/Objectives: Motile aeromonads are ubiquitous aquatic Gram-negative opportunistic pathogens with environmental, animal, aquatic, and human health implications. Methods: Motile aeromonads were isolated from village pond water samples (n = 100) of the Hisar district of Haryana state in India. Selective isolation and enumeration were followed by biochemical and genotypic identification using gyrB gene; evaluation of seven putative virulence factors and antimicrobial resistance studies and determination of extended spectrum beta lactamase (ESBL) and AmpC beta lactamase (ACBL) enzyme-producing abilities took place. Results: The viable counts of motile aeromonads varied from 1.6 × 10² CFU/mL to 1.2 × 10⁸ CFU/mL. Six species of Aeromonas were identified with high prevalence of A. veronii (74.7%), followed by A. caviae (8.9%), A. hydrophila (7.6), A. jandaei (5%), A. sobria (2.5%), and A. dhakensis (1.3%). PCR amplification of seven genes related to virulence indicated that the majority of the isolates were positive for enolase (eno, 98%), cytotoxic enterotoxin (act, 88%), and hemolysin (asa1, 86%). Many isolates were also positive for type III secretion system inner membrane component (ascV, 53%), ADP-ribosylating toxin (aexT, 47%), and extracellular hemolysin (ahh1, 4%). The antimicrobial resistance (AMR) profile of the isolated Aeromonas isolates indicated the high resistance observed to nalidixic acid (40.2%), cefoxitin (33%), and imipenem (6.2%). In addition, the occurrence of 10.3% ESBL, 32% ACBL, and 29.9% multi-drug resistant (MDR) isolates is alarming. Phylogenetic analysis of gyrB sequences of A. veronii isolates (n = 59) together with GenBank sequences of A. veronii from different geographical regions of the world indicated high genotypic diversity. Conclusions: the village aquaculture ponds in Hisar district have a high occurrence of MDR A. veronii, A. hydrophila, and A. caviae, posing significant animal and public health concern.