51 巻 (2016) Special-issue 号 p. S39-S45
The first isolation of Vibrio vulnificus biotype I from disease outbreaks in cultured tiger grouper Epinephelus fuscoguttatus Forsskal, 1775 in southern Thailand has been described. Gross signs of diseased fish included dark coloration of body, anorexia, petechial hemorrhages in the skin of the tail and fins and ulceration of the skin. Hemorrhagic septicemia was observed in intestine, body cavity and spleen. The 205-bp amplified DNA fragment of the hemolysin gene (vvhA) was detected from all of bacterial isolates, indicating V. vulnificus. Bacteria showed characteristics of biotype 1, the human clinical isolate, as indicated by their motility, positive results for indole production, ornithine decarboxylation activity, acid production from D-mannitol and growth at 42°C. The human virulence potential of V. vulnificus isolates using three biomarkers, 16S ribosomal ribonucleic acid (rRNA), vvhA gene and virulence-correlated gene (vcg), showed that genotypes of V. vulnificus was the clinical-type with two profiles. The susceptibility of tiger grouper to V. vulnificus isolate was performed by intraperitoneal injection (i.p.) with 106 CFU/mL bacterial suspensions. The experimentally injected tiger grouper had mortalities within 5 days post-injection and developed clinical signs similar to those found in disease outbreak. In a vaccination trial, the tiger grouper vaccinated with formalin inactivated whole-cell vaccine exhibited relative percent survival (RPS) of 68% following homologous isolate challenge. In conclusion, V. vulnificus biotype 1 strain that caused disease in tiger groupers is similar to V. vulnificus pathogenic to humans.