Phenotypic Characterization of Certain Flavobacteria Species Infected Cultured Freshwater Fish

Abstract

One of the most important and distributed bacterial disease in freshwater fish in Egypt is flavobacteriosis disease that caused by the gram-negative bacillus Flavobacterium which infects fish under stressful conditions and causing high mortality. In this study we have attempted to identify the possible infection of three flavobacteria app. (F. columnare, F. covae, and F. davissi) out of 200 cultured African catfish Clarias gariepinus and Nile tilapia tilapia niloticus. The Goal of this study was to isolate and characterize Flavobacteria species phenotypically, biochemically and detect the haemolytic virulence activity, beside evaluation antibiotics resistance activity of this bacterium. Despite, all flavobacteria species cause heamolysis to sheep blood agar that indicate to presence of heamolysine virulence gene but the F.columnare TIL2015 strain show no heamolysis on sheep blood agar. According to antibiotic sensitivity assay Gentamycin 30 μg, was the most effective antibiotic against the all tested Flavobacteria species, however F.columnare strains were sensitive against Doxycycline 30 μg, streptomycin 10 μg, beside gentamycin 30 μg. All isolates were resistant to amoxicillin 30 μg and Cefalexine 30 μg.