Description of isolated bacterial pathogens from diseased Cirrhinus mrigala

Abstract

The purpose of this study was to isolate and characterize the disease causative bacterial species from commercially important freshwater fish species, Cirrhinus mrigala. For this purpose, diseased C. mrigala samples were collected both from cultured and wild conditions. From sampled fish, extracted gills, liver, intestine and skin were homogenized in PBS buffer. Bacterial isolation was achieved by inoculating samples on nutrient agar plates using the method of pour plate and streak plate. Maximum total bacterial load was found 3.4 × 105. Bacterial isolates were identified using morphological, physiological and biochemical features. Gram stain, motility, catalase, starch hydrolysis, fermentation, Indole, Methyl red, Voges-Proskauer and Urease tests were performed for identification. In short, isolated bacteria were identified as Escherichia coli, Staphylococcus aureus, Bacillus cereus and Citrobacter freundii. Pathogenicity was confirmed in healthy fish by the use of reproduced isolate through experimental infection to fulfil Koch's postulates. Variations in organ structures were studied by histopathology and changes that were found to be lesions, tissue degenerations, necrotic and haemorrhages. This study will be supportive in formulating control measures for disease prevention and successful treatment for these pathogenic bacteria.