Lactococcus garvieae is a well-known fish pathogen in aquaculture, but is also found in other animals like cattle, poultry, pigs, dogs and cats. In recent years, it has emerged as an occasional human pathogen possibly as a result of zoonotic infection. The aim of this study was to use whole genome sequencing to characterise L. garviae causing human infection in Singapore to determine their likely source.
The genomic DNA of 11 local L. garvieae isolates (Fish = 6, Human = 5) were sequenced using Illumina MiSeq and assembled with Galaxy 18.05. An additional 17 whole genome sequences of L. garviae isolated overseas were included for comparative genome analysis. Resistance genes were identified using ABRICATE. Virulence genes identified in previously published literature were sought by BLAST search. Multilocus sequence typing was performed with SRST2 and the concatenated loci were aligned using MEGA 7.0 and a neighbour joining tree constructed. Genetic clusters (GCs) were inferred from the tree. Clonal complexes (CCs) were also identified by eBURST v3.
Two local isolates belonged to CC3. The rest were singletons, with 6 novel STs. Similarities were observed between the STs of local fish and human isolates with those of fish, food and human clinical isolates overseas. There were 3 GCs with local isolates distributed across all of them. Virulence genes (putative internalin and putative mucus adhesin) were found to be specific to GC2 and GC3. Antimicrobial resistance genes were more common in local isolates compared to those overseas.