Isolation and identification of pathogenic bacteria from Anguilla japonica mixedly infected with Edwardsiella tarda and Vibrio vulnificus.

Edwardsiella tarda and Vibrio vulnificus are pathogens that can infect both humans and animals. Two strains were isolated from the diseased Anguilla janponica cultivated in Humen,Guangdong province in March,2008. Strain AnGH080301 and AnGH080302 were confirmed to be the pathogen of the disease by challenge test. Traditional physiological and biochemical experiments were done,while API-ID32E system was also applied in the bacterial classification. The results showed that strain AnGH080301 and AnGH080302 were similar to Edwardsiella tarda and Vibrio vulnificus respectively in most of the phenotypes. In order to investigate the phylogenetic position of the pathogens,16S rRNA genes partial sequences of strain AnGH080301 and heat shock protein (HSP60) genes partial sequences of strain AnGH080302 were determined respectively. The results showed that the 16S rRNA gene sequences of strain AnGH080301 (FJ646618) was 1431 bp in length and its similarity with Edwardsiella tarda(AB050832) in GenBank was 99. 7 %. Phylogenetic tree of Edwardsiella based on 16S rRNA genes showed that strain AnGH080301 clustered together with Edwardsiella tarda. The HSP60 gene sequences of strain AnGH080302 (FJ646619) was 505 bp in length and its similarity with Vibrio vulnificus (BA000037) in GenBank was 99. 8 %. Phylogenetic tree of Vibrio based on HSP60 genes showed that strain AnGH080302 clustered together with Vibrio vulnificus. Based on the results obtained,the strain AnGH080301 and AnGH080302 were identified as Edwardsiella tarda and Vibrio vulnificus respectively,and it is the first report about the mixed infection of Edwardsiella tarda and Vibrio vulnificus in Anguilla janponica.