Identification and characterisation of pathogenic Vibrio splendidus from Yesso scallop (Patinopecten yessoensis) cultured in a low temperature environment.

A fatal disease with apparent lesions on the adductor muscles of Yesso scallop Patinopecten yessoensis has occurred for three consecutive years from 2009 to 2011 in the northeastern China. This disease has been suspected to be closely associated with bacterial infections. In the present study, 96 bacteria were isolated from the lesions of moribund scallops. They were grouped into Vibrio (88 strains), Moritella (5 strains), Pseudomonas (2 strains) and Shewanella (1 strain) by 16S rDNA sequencing. In the Vibrio group, Vibrio splendidus was the predominant species, consisting of 43 strains. A strain of V. splendidus, named JZ6, was identified as a potential pathogen because it possessed two important virulence factors, Vsm and OmpU. Stain JZ6 was cold-adapted, and could surviveand exhibit haemolytic activity from 4°C to 32°C, with the highest activity observed at 10°C. The pathogenicity of JZ6 was further confirmed by injection and immersion challenges to scallops at 10°C. The cumulative mortality rates in the two experiments were 80% and 45%, respectively, which were significantly higher (P<0.05) than those of control and blank groups. The disorganisation of muscle fibres in challenged scallops was observed to be histopathologically identical to that in moribund Yesso scallop collected from the same farm. The results indicate that V. splendidus is the predominantly culturable bacteria from the lesions of diseased Yesso scallop, and JZ6 probably is the pathogenic agent to Yesso scallop in this low temperature environment.