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

Abstract

Enterococcus s e n o h c ~d a is the causative agent of an enterococcal Infection in yellowtail Seriola q~llnqueradlata and IS antigen~cally classified into 2 phenotypes KG+ and KG-Phenotypic variation from K G to KG+ occurs readily on an artihcial medium The surface morphoIogies of the K G and KG+ phenotypes were differentiated by scanning electron microscopy KG-cells were more hydroph~lic than KG+ cells and were resistant to phagocytos~s by yellowtail head kidney phagocytes The c h e m ~l u m ~n e s c e n t response of these phagocytic cells was lower with the KG-phenotype than with the KG+ phenotype The immune responses of yello.ruta11 f o l l o ~~i n g injection of the 2 phenotypes differed h ~g h e r agglutinating titers were o b t a ~n e d with the KG+ phenotype compared to the KGphenotype Thus, the cell surface may function as an anti-phagocytic factor in E seriolic~da and apparently affects ~t s immunogeniclty