Lactococcus garvieae: Introduction, Pathogenicity, Lab Diagnosis

Introduction

Table of Contents

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).

Fig. Lactococcus garvieae growth on CLED agar of urine culture

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

Gram positive cocci of Lactococcus garvieae in Gram staining of culture at a magnification of 1000X — Fig. Gram-positive cocci of Lactococcus garvieae in Gram staining of culture at a magnification of 1000X

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 positive cocci of Lactococcus garvieae in Gram staining of culture at a magnification of 4000X — Fig. Gram-positive cocci of Lactococcus garvieae in Gram staining of culture at a magnification of 4000X

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

Culture Characteristics

Again, Lactococcus garvieae grew on CLED agar after repetition of urine culture — Fig. Again, Lactococcus garvieae grew on CLED agar after repetition of the urine culture

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

Gram positive cocci of Lactococcus garvieae in Gram staining of repeated culture at a magnification of 4000X — Fig. Gram-positive cocci of Lactococcus garvieae in Gram staining of repeated culture at a magnification of 4000X

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)

Fig. Lactococcus garvieae antimicrobial susceptibility result

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.

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