The identification and determination of toxin genes of Vibrio strains causing hemorrhagic disease on red drum ( Sciaenops ocellatus ) using PCR

Data were collected from 30 strains of Vibrio and sampled on different organs (brain, hemorrhagic site and digestive tract) of Sciaenops ocellatus infection. The results showed that the nucleotide sequences 16S rRNA region are highly similar to those of V. alginolyticus , V. azureus , V. fluvialis, V. natriengens and V. orientalis, which were published on Genbank and other, ranging from 98.05 to 100%. The digestive tract has the most common Vibrio strains ( V. alginolyticus [16] V. azureu s [7] and V. fluvialis ). Thereout, 25 of 30 strains of Vibrio contained 1 to 3 toxin genes, except V. parahaemolyticus . Six parameters were used to measure the DNA polymorphism of 33 homologous DNA sequences in this Vibrio bacteria population. The results indicated that number of separate polymorphic sites (S), total number of mutant sites (Eta), number of haplotype (h), haplotype diversity (Hd), average number of nucleotide differences (k), nucleotide diversity (Pi) were 98 (S), 103 (Eta), 9 (h), 0.887 ± 0.032 (Hd), 25.789 (k) and 17.980 × 10–3 ± 0.003 (Pi), respectively (P < 0,05). The G + C content above 1434 sites positions of nucleotide sequences accounted for 0.542. The phylogenetic tree showed that these strains are divided into six groups. As observed, the appearance of isolated Vibrio on 3 organs of fish ( S. ocellatus ) hemorrhagic are V. azureus (27,67%), V. alginolyticus (50%), V. orientalis (6,67%) and V. fluvialis (16,67%). Through this result, we found that the diversity of Vibrio species that appeared on the red drum was used in the 16S rRNA region and the presence of toxin genes in these Vibrio species.