Biodiversity of Lactococcus garvieae strains isolated from fish in Europe,Asia, and Australia

Lactococcus garvieae (junior synonym, Enterococcus seriolicida) is a major pathogen of fish, producing fatal septicemia among fish species living in v ery diverse environments. The phenotypic traits oft. garvieae strains colle cted from three different continents (Asia, Europe, and Australia) indicate d phenotypic heterogeneity. On the basis of the acidification of D-tagatose and sucrose, three biotypes were defined. DNA relatedness values and a spe cific PCR assay showed that all the biotypes belonged to the same genospeci es, L. garvieae. All of the L. garvieae strains were serotyped as Lancefiel d group N. Ribotyping proved that one clone was found both in Japan, where it probably originated, and in Italy, where it was probably imported. PCR o f environmental samples did not reveal the source of the contamination of t he fish in Italy. Specific clones (ribotypes) were found in outbreaks in Sp ain and in Italy. The L. garvieae reference strain, isolated in the United Kingdom from a cow, belonged to a unique ribotype. L. garvieae is a rising zoonotic agent. The biotyping scheme, the ribotyping analysis, and the PCR assay described in this work allowed the proper identification of L. garvie ae and the description of the origin and of the source of contamination of strains involved in outbreaks or in sporadic cases.