Characterization of <i>Flavobacterium columnare</i> isolated from clinical dermatopathy of farmed <i>Clarias gariepinus</i> in Oyo State, Nigeria

Abstract

Diagnosis of columnaris disease has been presumptive due to difficulty in isolating Flavobacterium columnare, the fastidious causal agent. This study, therefore aimed at isolation and characterization of the etiological agent of the disease to achieve definitive diagnosis and effective control. Standard clinical and bacteriological methods were used to examine 80 purposively selected Clarias gariepinus with signs of dermatopathy, from three different culture systems observed in 8 fish farms in Oyo State, Nigeria. Inocula from skin and gill lesions of sampled fish were cultured at 28^oC for 48hrs on modified nutrient agar and cytophaga agar. Isolates characterized morphologically and biochemically were further identified with PCR technique using 16-S rRNA gene-based primers with expected band size of 1193 base pairs. Twenty-five (31.25%) typical yellow, rhizoid-edged colonies with the bacterium that exhibited flexing motility, nitrate reduction, gelatin degradation and H2S production were isolated. Molecular characterization by PCR revealed specific DNA products with the expected band size for the 25 F. columnare isolates. This study achieved the isolation and characterization of Flavobacterium columnare in farmed Clarias gariepinus in Oyo State, Nigeria is using the modified selective nutrient agar, providing the basis for antibiogram and genetic manipulation of this important pathogen.