Isolation of Lactococcus garvieae Showing No Agglutination with Anti-KG⁻ Phenotype Rabbit Serum

Lactococcus garvieae-like bacteria, which did not agglutinate with a rabbit antiserum against L. garvieae capsulated cells (KG- phenotype cells), were isolated from diseased yellowtail Seriola quinqueradiata in 2012. The non-agglutinating L. garvieae-like bacteria reacted positively in a species-specific PCR targeting the 16S rRNA gene of L. garvieae. DNA-DNA relatedness values between reference L. garvieae strains and the non-agglutinating strains were higher than 70%. Almost complete sequencing of the 16S rRNA gene of the non-agglutinating strains revealed high similarity with that of L. garvieae ATCC49156. The non-agglutinating strains showed the same morphological and biochemical characteristics as reference L. garvieae strains. These results confirm that the non-agglutinating strains are L. garvieae. However, the present strains differed from the reference strains in terms of the lytic bacteriophage susceptibility. Serological analysis revealed that autoclave-extracted cellular antigens of the non-agglutinating strains did not react to antiserum raised against L. garvieae KG- phenotype cells. Although the non-agglutinating strains were isolated from different prefectures, they showed similar patterns in biased sinusoidal field gel electrophoresis (BSFGE).