Molecular characterization and pathogenicity of a virulent Acinetobacter baumannii associated with mortality of farmed Indian Major Carp Labeo rohita (Hamilton 1822)

Indian Major Carp Labeo rohita (Ham.) is the most preferred cultivable fish species under freshwater aquaculture in India. The present study was conducted to characterize the bacteria at molecular level and to understand its pathogenicity associated with mortality of farmed rohu, Labeo rohita. Diseased fish samples were collected from cultured ponds of Nadia, West Bengal, India for the isolation of the pathogen. The 16S rRNA gene sequence of the bacteria revealed that the isolate was 100% identical with Acinetobacter baumannii (NCBI Accession Number KT156752). Intraperitoneal injection with the isolate at the level of 2.1 × 108 cells/ml in fish causes mortality. The challenged fish had loss of mucus and reddish lesion near the pectoral fin, however there was no sign in the gill. The histology of experimentally challenged Labeo rohita showed hemorrhages and shrunken glomeruli with densely basophilic nuclei in kidney whereas degenerated hepatic tissue and increased hepatocyte vacuolation in liver. This study underlines the first time involvement of Acinetobacter baumannii in the disease outbreak of Labeo rohita. The pathology and pathogenesis studies of this emerging pathogen in cultured carps would help in management of the outbreak of disease in aquaculture.