Flavobacterium columnare (F.columnare) is an important pathogen affecting gills and skin of freshwater fishes causing columnaris disease. The objective of the study to isolate F.columnare from Nile tilapia and study the prevalence of antibiotics resistance strains with genotypic identification of β-lactamase resistance genes (blaTEM, bla SHV) and tetracycline resistance gene (tetA) among isolated strains of F.columnare. Two hundred diseased fish were randomly collected from different localities throughout year (2018-2019). F. columnare showed seasonal prevalence 0.00%, 10%, 40.00%, and 20.00% in winter, spring, summer and autumn respectively with total prevalence 35/200 (17.5%). F.columnare was isolated in high percent from skin and gills and rare in internal organs. The invitro antibacterial sensitivity test was applied on 20 F.columnare isolated strains and revealed resistant to pencillin, cephalosporin, aminoglycoside, nitrofurans, polymixinB and tetracycline. The isolated strains have three antibacterial resistance genes, bla TEM with amplicon size 516bp, bla SHV with amplicon size 392bp and tetA with amplicon size 576bp.
Conclusion: According to this study tested strains were resistant to multiple antibiotics and their genes were widely distributed, so phenotypic and genotypic characterization of antibiotic resistant strains of isolated F. columnare are similar.