Development of a selective and differential medium for capsulated Lactococcus garvieae

Area of Science:

• Microbiology
• Veterinary Science
• Aquaculture

Background:

• Lactococcus garvieae is a significant pathogen in fish and shellfish.
• Accurate and rapid diagnostic methods are crucial for controlling L. garvieae outbreaks.
• Existing methods for L. garvieae identification can be time-consuming and lack specificity.

Purpose of the Study:

• To develop and evaluate a selective and differential medium for Lactococcus garvieae.
• To assess the medium's specificity and ability to differentiate L. garvieae from other species.
• To determine the medium's utility in distinguishing between virulent and non-virulent strains.

Main Methods:

• Development of LG agar, a selective and differential culture medium.
• Testing the growth of L. garvieae and 38 other bacterial species on LG agar.
• Differentiation of L. garvieae from other bacteria based on colony morphology (black colonies with red halos).
• Confirmation of identification using conventional tests and 16S rDNA sequencing.
• Evaluation of the medium's ability to differentiate capsulated (pathogenic) from non-capsulated L. garvieae strains.

Main Results:

• LG agar successfully isolated all 14 tested strains of L. garvieae.
• Only 9 out of 148 strains from 38 other species grew on LG agar.
• The nine non-L. garvieae strains were easily differentiated by colony appearance.
• Colonies from mixed cultures and infected fish confirmed as L. garvieae by LG agar and further testing.
• LG agar differentiated capsulated L. garvieae strains from non-capsulated ones by colony appearance.

Conclusions:

• LG agar is a highly specific and differential medium for Lactococcus garvieae.
• The medium facilitates presumptive identification of L. garvieae through distinct colony morphology.
• LG agar shows significant potential for the primary isolation and presumptive identification of L. garvieae from various sample types.