Genomic analysis of Lactococcus garvieae isolates

Abstract

Lactococcus garvieae is a well-known fish pathogen, and in recent years, a human pathogen of increasing clinical significance. However, not much is known about the variances in characteristics of strains isolated locally and overseas. This study aims at conducting comparative genomic analysis on local and overseas L.garvieae isolates, to further understand the phylogenetic and virulence variances between the two groups. The genomic DNA of 11 local L.garvieae isolates (fish 6, human 5) were sequenced, annotated and typed using multi-locus sequence typing (MLST). A total of six novel sequence types (STs) were found in the local isolates. Genotypic overlapping of the STs was observed between local fish and human isolates with overseas fish, food and human clinical isolates. Thereby, suggesting a possible transmission between fish or food and humans. Virulence genes (putative internalin and putative mucus adhesin) were found to be specific to genomic clusters (GC), GC2 and GC3. A higher incidence of resistance genes was also observed in local isolates (n=8, 72.72%) when compared to the overseas isolates (n=7, 41.18%). This study represents the first evidence of genetic variances amongst local and overseas isolates, and virulence characteristics specific to the phylogeny of L.garvieae.