Molecular identification and pathogenicity study of virulent Vibrio cholerae non O1/O139 serotype associated with mortality of farmed Labeo rohita (Hamilton, 1822), in India

Vibrio cholerae is a gram-negative bacteria known for causing epidemics and pandemics conditions, comprised of both non-pathogenic and pathogenic strains. The present study identified a non O1, non-O139 V. cholerae (EMM1) serotype isolated from diseased Labeo rohita cultured in a wetland system at Purba Medinipur district, West Bengal, India. Identification of the isolate was done by biochemical test, 16S rRNA gene sequencing and phylogenetic analysis. The in vivo challenge experiment revealed that intraperitoneal injection of EMM1 serotype at a dose of 1.04× 10 7 CFU/ml resulted in 100% mortality of L. rohita . Furthermore, the presence of hlyA and rtxA virulent genes, confirmed by sequencing, in V. cholerae (EMM1) serotype might be, atleast partially involved in the mortality of L. rohita . In histological analysis, we found that EMM1 serotype challenge had a significant effect in L. rohita like degenerated hepatocytes in the liver, shrunken glomeruli in the kidney, necrosis of the intestinal villi epithelium and degeneration of muscle bundle were observed. Overall, the study demonstrated that, V. cholerae (EMM1) serotype is a potent aquatic microbial pathogen and draws the attention for proper management to prevent the possible occurrence of disease in aquaculture. • First report on occurrence of pathogenic Vibrio cholerae (EMM1) serotype in diseased Labeo rohita from India • In vivo challenge experiment shows high mortality in L. rohita • The presence of hlyA and rtxA virulent genes might be, at least partially, involved in the mortality of L. rohita . • The findings demonstrated that V. cholerae is a potential aquatic pathogen and proper management measure must be developed to avoid mortality and economic losses in aquaculture.