Genotypic Characterization and Resistance Patterns of Flavobacterium columnare from Pond-cultured Clarias gariepinus

Flavobacterium columnare is a significant fish pathogen of economic importance. Although, many studies have been done on Flavobacterium columnare in other countries, little or no investigation has been carried out in Nigeria especially on Clarias gariepinus associated Flavobacterium columnare infections. This study was undertaken to investigate the occurrence of Flavobacterium columnare in pond-cultured Clarias gariepinus and to determine their antibiotics susceptibility and resistance patterns. Swabs were aseptically taken from the kidney, liver, gills, skin and intestine of the affected fish samples, and analyzed microbiologically. After series of biochemical test, 58 out of 75 bacterial isolates recovered were presumptively identified as Flavobacterium columnare. Confirmatory identification of the isolates was carried out with previously described primers using multiplex PCR. Standard Kirby-Bauer disc diffusion method was used for antibiotics susceptibility test. Flavobacterium columnare isolates were 100% resistant to Streptomycin, Oxytetracycline, Chloranphenicol, Pefloxacin, Ofloxacin and 90, 70 and 60% resistant to Gentamycin, Amoxycillin and Clindamycin respectively. However, all the isolates were 100% susceptible to Ciprofloxacin and Cotrimoxazole only. The results revealed multiple drug resistance of the isolates to the antibiotics tested as the isolates were resistant to eight out of ten antibiotics used in this study. There are fewer studies on antibiotic resistance in Flavobacterium columnare from aquaculture enterprises and this study provides further support to the view that there is a potential risk of transfer of resistant bacteria and their genes to human pathogen through the food chain. Although, in Nigeria there is no antibiotic product registered for aquaculture usage, yet fish farmers use them off-label for bacterial diseases prevention.

Keywords: Flavobacterium columnare, Antibiotic Resistance, Clarias gariepinus, Multiplex PCR.

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