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Diseases of Aquatic Organisms

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DAO 25:81-86 (1996)  -  doi:10.3354/dao025081

Phenotypic variation associated with an anti-phagocytic factor in the bacterial fish pathogen Enterococcus seriolicida

Yoshida T, Eshima T, Wada Y, Yamada Y, Kakizaki E, Sakai M, Kitao T, Inglis V

Enterococcus seriolicida is the causative agent of an enterococcal infection in yellowtail Seriola quinqueradiata and is antigenically classified into 2 phenotypes, KG+ and KG-. Phenotypic variation from KG- to KG+ occurs readily on an artificial medium. The surface morphologies of the KG- and KG+ phenotypes were differentiated by scanning electron microscopy. KG- cells were more hydrophilic than KG+ cells and were resistant to phagocytosis by yellowtail head kidney phagocytes. The chemiluminescent response of these phagocytic cells was lower with the KG- phenotype than with the KG+ phenotype. The immune responses of yellowtail following injection of the 2 phenotypes differed: higher agglutinating titers were obtained with the KG+ phenotype compared to the KG- phenotype. Thus, the cell surface may function as an anti-phagocytic factor in E. seriolicida and apparently affects its immunogenicity.

Enterococcus seriolicida . Seriola quinqueradiata . Phagocytosis . Chemiluminescence . Immune response

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