Infectious Disease and Microbiology – Corynebacterium pseudotuberculosis

Overview

Corynebacterium pseudotuberculosis is an aerobic Gram-positive bacillus that primarily causes disease in animals and is only a rare cause of human infection. Human disease is usually associated with occupational or environmental exposure to infected animals.

The characteristic human manifestation is suppurative granulomatous lymphadenitis.

Microbiologic Characteristics

C. pseudotuberculosis is an aerobic, Gram-positive bacillus belonging to the genus Corynebacterium.

It is primarily an animal pathogen, with humans serving as accidental hosts following zoonotic exposure.

Epidemiology

Human infection is rare.

Most cases occur in people with significant contact with animals, particularly individuals whose occupations involve livestock or animal handling.

Potential exposure groups include:

• Farmers

• Veterinarians

• Abattoir workers

• Animal handlers

• Other individuals with close livestock exposure

Transmission

Human infection generally follows exposure to infected animals or contaminated animal material.

The organism may enter through breaks in the skin and subsequently spread through lymphatic channels to regional lymph nodes.

Suppurative Granulomatous Lymphadenitis

The classic human infection is suppurative granulomatous lymphadenitis.

Affected lymph nodes may become:

• Enlarged

• Painful or tender

• Inflamed

• Suppurative

• Chronically infected

The disease can resemble other causes of chronic granulomatous lymphadenopathy.

Differential Diagnosis

Important alternative causes of chronic or suppurative lymphadenitis include:

• Tuberculosis

• Nontuberculous mycobacterial infection

• Cat-scratch disease

• Tularemia

• Fungal infection

• Other bacterial lymphadenitis

A history of animal exposure provides an important clue to C. pseudotuberculosis infection.

Diagnosis

Definitive diagnosis is established by culture of material obtained from the infected lymph node or another appropriate specimen.

The organism can be cultured on:

Blood agar incubated with approximately 10% CO₂

Microbiologic identification is important because the clinical appearance can mimic several other causes of granulomatous lymphadenitis.

Treatment

Macrolide antibiotics may be used for C. pseudotuberculosis infection.

Treatment is often combined with appropriate management of the infected lymph nodes.

Surgical Management

Excision of infected lymph nodes may be necessary, particularly when lymphadenitis is persistent, suppurative, or inadequately responsive to antimicrobial therapy.

Thus, effective management may require both:

Antimicrobial therapy + surgical excision

Additional Treatment

Alternative antimicrobial agents include:

• Tetracyclines

• Penicillin G

Whenever possible, treatment of significant infection should be guided by culture and antimicrobial susceptibility results.

High-Yield Clinical Pattern

Animal or livestock exposure

• ●

Chronic enlarged lymph nodes

• ●

Suppurative granulomatous lymphadenitis

→ Think Corynebacterium pseudotuberculosis

Exam Essentials

Organism: Corynebacterium pseudotuberculosis

Type: Aerobic Gram-positive bacillus

Transmission: Zoonotic exposure, usually involving animals

Human infection: Rare

Classic manifestation: Suppurative granulomatous lymphadenitis

Diagnosis: Culture

Culture condition: Blood agar with approximately 10% CO₂

Treatment: Macrolide antibiotic

Source control: Excision of infected lymph nodes when indicated

Alternatives: Tetracycline or penicillin G

Key clinical pearl: The combination of animal exposure and chronic suppurative granulomatous lymphadenitis should raise suspicion for Corynebacterium pseudotuberculosis.