Distribution of multi-virulence factors among Aeromonas spp. isolated from diseased Xiphophorus hellerii

Changes in water quality and environmental factors have been reported to play key roles on the health and disease susceptibility of the ornamental fish Xiphophorus hellerii (sword tail). This can further be decided by the natural distribution of pathogens with enhanced virulence properties in the aquatic system. As Aeromonas spp. are the major fish pathogens, a detailed analysis on its association with the disease of X. hellerii was conducted in the study. Here, bacterial isolation has been carried out from the surface, gill and intestine of diseased fish, and also from water samples. The twelve bacterial isolates obtained were identified biochemically and also by 16S rDNA sequence analysis as Aeromonas spp.. Among the various virulence properties screened by in vitro and PCR-based methods, most of the Aeromonas spp. were found to be positive for multiple virulence properties. Further disease challenge using the highly virulent Aeromonas veronii XhG1.2 in X. hellerii showed remarkable histopathological changes of the gill, liver, and intestine in the treated fish. This confirmed the hyper-pathogenic potential of XhG1.2 as the disease occurred within a short period of 24 h. The identification of broad range of virulence factors among the fish pathogenic bacterial isolates of aquatic environment indicates the need for periodic screening to predict the threat to aquatic life especially fish.