Characterization of Lactococcus garvieae isolated from radish and broccoli sprouts that exhibited a KG+ phenotype, lack of virulence and absence of a capsule

Abstract

Aims: To identify Lactococcus garvieae isolates from radish and broccoli sprouts and compare them with virulent and less virulent mutant strains obtained from yellowtails with regard to KG phenotype, presence of a capsule and virulence towards yellowtails and mice.

Methods and results: Comparative 16S rRNA gene sequence analysis of six isolates obtained from radish and broccoli sprouts indicated that they were L. garvieae (similarity >99%). They were compared with KG9502, Lg2 and ATCC49156 strains obtained from yellowtails. A less virulent mutant strain Lg2-S was obtained by Lg2 subculture. Biochemical characterization of the six strains resembled that of KG9502, Lg2, ATCC49156 and Lg2-S, except for saccharose and tagatose acidification and the presence of hippuricase. These six strains were nonpathogenic towards yellowtails and mice, nonsusceptible to bacteriophages and demonstrated heterogeneity on pulsed-field gel electrophoresis analysis. Using transmission electron microscopy, a capsule was observed in KG9502 and Lg2 but not in ATCC49156 and Lg2-S.

Conclusions: We isolated L. garvieae strains that lacked pathogenicity towards yellowtails and mice from radish and broccoli sprouts; these were noncapsulated and exhibited KG(+) phenotype.

Significance and impact of the study: This is the first documentation of L. garvieae isolated from terrestrial plants. These isolates exhibited genetic diversity; however, they were noncapsulated and nonpathogenic towards yellowtails and mice.