Lactococcus garvieae: Introduction, Pathogenicity, Lab Diagnosis

Lactococcus garvieae: Introduction, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

Introduction

Lactococcus garvieae is a Gram-positive, coccoid, facultative anaerobic bacterium causing lactococcosis, a major, often fatal, hemorrhagic septicemia in cultured fish (especially trout and yellowtail) when water temperatures exceed. As an emerging zoonotic pathogen, it causes sporadic, serious human infections (e.g., endocarditis).

Classification: Family Streptococcaceae.
Habitat: Ubiquitous; found in aquatic environments, fish, cattle (mastitis), and swine.
Impact: Causes massive economic losses in aquaculture worldwide due to high mortality (up to 50%).

Pathogenicity

Disease: Hyperacute and hemorrhagic septicemia.
Clinical Signs in Fish: Exophthalmia (pop-eye), erratic swimming, darkening of skin, hemorrhage in the gills, fins, and anus.
Virulence Factors: Capsules, hemolysins, adhesins (e.g., pav, psaA), superoxide dismutase, and biofilm formation.
Transmission: Horizontal transmission via water, fecal-oral route, and contaminated feed.

Laboratory Diagnosis of Lactococcus garvieae

Samples: Kidney, spleen, heart, blood, or brain tissue.
Culture: Grows on Blood Agar (colonies are small, white, alpha-hemolytic) and specialized media.
Biochemical: Gram-positive, Catalase-negative, -leucine-naphthylamide-positive.
Molecular: PCR-based protocols, 16S rRNA gene sequencing, and RAPD for typing.
Serotyping: Differentiation of pathogenic (capsulated) and non-pathogenic (non-capsulated) strains.

Treatment

Antibiotics commonly used include florfenicol, amoxicillin, and erythromycin.
Resistance: Increasing, with reports of resistance to tetracycline, streptomycin, and trimethoprim.
Alternatives include phage therapy, probiotics, and, in some cases, herbal extracts.

Prevention

Vaccination: Commercial and autogenous bacterins are effective, particularly in injection form.
Husbandry: Lowering water temperature, reducing fish density, removing dead fish, and improving water quality.

Keynotes on Lactococcus garvieae

Temperature Sensitivity: Outbreaks typically occur during warm summer months.
Emerging Zoonosis: While historically a fish pathogen, it is now recognized to affect humans, usually elderly patients or those with underlying diseases.
Host Range: Affects trout, tilapia, yellowtail, olive flounder, and occasionally, mammals.
Dairy Association: Originally isolated from bovine mastitis.

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