Screening for the high virulent bacterial isolates caused white patch disease in striped catfish (Pangasianodon hypophthalmus)

Abstract

Bacterium Flavobacterium columnare was recovered and identified as the aetiologicalagent causing white patch disease in farmed striped catfish (Pangasianodonhypophthalmus) fingerlings that had suffered high mortality rates within a commercialhatchery in Vietnam. This study arrived to determine the high virulencebacterialisolates caused white patch disease in striped catfish. The gross clinical signsweretypical of F. columnare infected fish such as gill necrosis, fin and tail erosions. Thebacteria were isolated on anacker and ordal (AO) agar plates isolated ontheagarproduced yellow-pale colonies, flat that rhizoid edges after 48h at 28 0C. Therefore, anexperimental immersion challenge study was performed with doses rangingfrom103-10 6 cfu/ml to evaluate the LD50. In addition, The yellow-pigmented bacteriawereisolated and identified as F. columnare using the PCR method. Furthermore, toprevent, control, and white patch disease, the study also performed antibiogramsandused seven types of antibiotics to test susceptibility on five bacterial strains. Theantibiogram results did not find any resistance to doxycycline and chloramphenicol.Over 80% of the bacteria were still sensitive to ampicillin, trimethoprim-sulfamethoxazole, and florfenicol. Over 60% of the F. columnare strainsweresensitive to rifampicin and levofloxacin.