First isolation, pathogenicity, and draft genome sequences of Lactococcus garvieae serotype III from cobia...

Area of Science:

• Aquatic Animal Health
• Bacteriology
• Fish Disease

Background:

• Lactococcus garvieae is a significant pathogen in marine aquaculture.
• A novel serotype III of L. garvieae has been identified in several fish species.
• Lactococcosis poses a threat to commercially important fish stocks.

Purpose of the Study:

• To report the first isolation of L. garvieae serotype III from cage-cultured cobia (Rachycentron canadum).
• To assess the pathogenicity of L. garvieae serotype III isolates in cobia, yellowtail (Seriola quinqueradiata), and amberjack (Seriola dumerili).
• To characterize the genomic features of the isolated L. garvieae serotype III strains.

Main Methods:

• Isolation and identification of L. garvieae serotype III from diseased cobia.
• Experimental infection trials in cobia, yellowtail, and amberjack to determine pathogenicity.
• Whole-genome sequencing and analysis of the L. garvieae isolates.

Main Results:

• L. garvieae serotype III isolates (LC2313 and LC2323) were successfully isolated from diseased cobia exhibiting hemorrhagic eyes and curved spine.
• Infectivity trials demonstrated significant mortality in cobia (30-60%) and high mortality (up to 100%) in yellowtail and amberjack.
• Genomic analysis revealed close relatedness to other L. garvieae serotype III strains, with each isolate possessing approximately 1800 coding sequences and 12 phage-related genes.

Conclusions:

• L. garvieae serotype III is pathogenic to cobia, yellowtail, and amberjack, confirming its role in fish mortality.
• The findings highlight the potential for disease transmission among different marine fish species.
• Increased awareness and effective disease management strategies are crucial for mitigating the impact of L. garvieae serotype III in aquaculture.