Pathogenicity of an invasive bacterium, Aeromonas salmonicida in Indian major carp, Labeo rohita – Evaluation of immune response using effective molecular markers

Abstract

Effects of Aeromonas salmonicida on the non-specific immune response, oxidative stress and subsequent cell death in liver and spleen of Labeo rohita exposed to asymptomatic dose (2 × 107 CFU/mL) of pathogen were studied. Evaluation of in vivo non-specific immunity via Nitro blue tetrazolium (NBT) reduction assay, myeloperoxidase (MPO) assay and serum bactericidal activity assay exhibited significant alterations among infected fishes, indicating temporary surge of innate immune responses. Considerable cell death and damage was observed in the histopathological analysis of liver and spleen in the infected fishes. Flow cytometric analysis by FITC-Annexin V/PI conclusively indicated triggering of apoptotic cell death in both organs. Relative expression of pro-inflammatory cytokine (TNFα) gene, antimicrobial protein producing genes (Lysozyme C and Lysozyme G) and apoptosis effector molecule (Caspase 3) gene were increased significantly both in liver and spleen of A. salmonicida treated fishes. In conclusion, infection with A. salmonicida at asymptomatic level resulted in severe oxidative stress that, caused apoptotic cell death. Since facultative pathogen eradication is not possible in open water or flow-through aquaculture systems, this remains a crucial area of scientific research and the results obtained in the present study might provide better understanding of prophylactic, diagnostic and therapeutic measures during aquaculture.