Lactococcus garvieae is the etiological agent of lactococcosis, a clinically and economically
significant infectious disease affecting farmed rainbow trout. L. garvieae had been considered the only
cause of lactococcosis for a long time; however, L. petauri, another species of the genus Lactococcus,
has lately been linked to the same disease. The genomes and biochemical profiles of L. petauri and
L. garvieae have a high degree of similarity. Traditional diagnostic tests currently available cannot
distinguish between these two species. The aim of this study was to use the transcribed spacer
(ITS) region between 16S rRNA and 23S rRNA as a potential useful molecular target to differentiate
L. garvieae from L. petauri, saving time and money compared to genomics methods currently used as
diagnostic tools for accurate discrimination between these two species. The ITS region of 82 strains
was amplified and sequenced. The amplified fragments varied in size from 500 to 550 bp. Based on
the sequence, seven SNPs were identified that separate L. garvieae from L. petauri. The 16S-23S rRNA
ITS region has enough resolution to distinguish between closely related L. garvieae and L. petauri and
it can be used as a diagnostic marker to quickly identify the pathogens in a lactococcosis outbreak.


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