Identification and phylogenetic analysis of Vibrio vulnificus isolated from diseased Trachinotus ovatus in cage mariculture

In October 2005, an infectious disease occurred as outbreaks of high mortality within one week, which was responsible for important economic losses in intensive culture of Trachinotus ovatus around the Gulf Coast of Yangjiang city (Guangdong Province, China). The present study documented the causative agent of the diseased fish suffering from external haemorrhages and ulcers, haemorrhagic gills, livers and intestine. The strain was isolated from the diseased fish by ZoBell 2216 E agar and confirmed the pathogenicity by challenge experiments. Biochemically, the strain showed properties and biochemical characteristics similar to Vibrio vulnificus, with the exception of several atypical biochemical characteristics, especially the sucrose-positive. Meanwhile, sequencing of the 16S rRNA gene and the hemolysin gene revealed that the isolated strain was highly homogeneous with V. vulnificus. To sum up, the isolated strain was confirmed as V. vulnificus on the basis of phenotypic characteristics, phylogenetic analysis of the 16S rRNA sequences and sequence analysis of the hemolysin gene. To our knowledge, this is the first report on the V. vulnificus infection in T. ovatus.