Since 2012,
Lactococcus garvieae strains which do not agglutinate with anti-KG
– phenotype rabbit serum have been isolated from cultured yellowtail
Seriola quinqueradiata and greater amberjack
S. dumerili in Japan. In this study, pathogenicity of non-agglutinating
L. garvieae was confirmed by intraperitoneal injection into these fish species. Cross-protective responses of yellowtail to the KG
– phenotype and non-agglutinating strains were also examined. Yellowtail were immunized with formalin-killed cells (FKC) prepared from both types. Three weeks after immunization, the fish were challenged with the KG
– phenotype and non-agglutinating strains. Each type of FKC provided effective protection against infection with the homologous strain. The protection level of the KG
– phenotype FKC was relatively lower against the non-agglutinating strain than against the homologous KG
– phenotype and the non-agglutinating type FKC was ineffective against the KG
– phenotype. In conclusion, we propose two serotypes (I and II) of
L. garvieae isolated from marine fish species in Japan. Serotype I which agglutinates with anti-KG
– phenotype serum is typical
L. garvieae and divided into Ia and Ib, which are KG
– (capsulated) and KG
+ (non-capsulated) phenotypes, respectively. Serotype II which does not agglutinate with the anti-KG
– serum is a new type in fish pathogenic
L. garvieae.
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