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

Introduction

Lactococcus garvieae is a Gram-positive, catalase-negative, non-spore-forming coccus, typically arranged in pairs or short chains. It belongs to the lactic acid bacteria group and is well known as a major pathogen in fish (lactococcosis).

In humans, it is an emerging opportunistic pathogen, increasingly recognized due to improved identification methods such as MALDI-TOF MS.

Pathogenicity

• Zoonotic potential, commonly linked to:
  • Consumption of raw or undercooked fish/seafood
  • Occupational exposure (fish handlers, aquaculture workers)
• Predisposing factors:
  • Immunocompromised state
  • Valvular heart disease
  • Malignancy
  • Diabetes mellitus
• Reported human infections:
  • Infective endocarditis
  • Bacteremia/septicemia
  • Urinary tract infection
  • Cholangitis
  • Peritonitis
• Pathogenicity is low to moderate, largely dependent on host susceptibility

Laboratory Diagnosis

Specimens

• Blood, urine, bile, ascitic fluid, wound swab (as clinically indicated)

Microscopy

• Gram stain: Gram-positive cocci in pairs or short chains
• Catalase: Negative

Culture Characteristics

• Blood agar: small, grayish, non-hemolytic or α-hemolytic colonies
• Grows at 25–37°C
• Does not tolerate high salt (helps differentiate from Enterococcus)

Biochemical Features

• PYR: usually negative
• Bile esculin: negative
• Can be misidentified as Enterococcus or Streptococcus

Confirmatory Identification

• MALDI-TOF MS (method of choice)
• 16S rRNA gene sequencing (gold standard)

Treatment

• Generally susceptible to beta-lactam antibiotics
• Common treatment options:
  • Penicillin
  • Ampicillin
  • Amoxicillin
  • Ceftriaxone
• Severe infections (e.g., endocarditis):
  • Beta-lactam ± aminoglycoside (based on AST)

• Antimicrobial susceptibility testing is essential due to variable resistance patterns.

Prevention

• Avoid consumption of raw or undercooked fish.
• Proper food hygiene and cooking practices.
• Protective measures for aquaculture and fish industry workers.
• Early identification and treatment in high-risk patients.
• Strict aseptic techniques in hospitals.

Keynotes

• Emerging zoonotic opportunistic pathogen.
• Commonly misidentified without advanced diagnostics.
• Strong association with fish exposure.
• An important cause of infective endocarditis.
• Detection is increasing with MALDI-TOF and molecular tools.

Further Readings

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC7455392
2. https://en.wikipedia.org/wiki/Lactococcus_garvieae
3. https://www.mdpi.com/2076-0817/13/1/49
4. https://www.sciencedirect.com/topics/immunology-and-microbiology/lactococcus-garvieae
5. https://www.researchgate.net/publication/275330542_Lactococcus_garvieae_a_small_bacteria_and_a_big_data_world
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC8289619
7. https://onlinelibrary.wiley.com/doi/10.1111/j.1742-1241.2006.00855
8. https://www.researchgate.net/publication/311088571_Lactococcus_garvieae_An_emerging_bacterial_pathogen_of_fish
9. https://www.cureus.com/articles/331535-urinary-tract-infection-caused-by-lactococcus-garvieae-in-a-75-year-old-male-patient-with-a-complex-medical-history
10. https://www.mdpi.com/2076-2615/10/9/1609