Bacillus, Listeria, and Erysipelothrix Overview

Bacillus

• Large gram positive spore-forming rods
• Found in soil and water
• Only Bacillus anthracis is an obligate pathogen; others are opportunistic

Bacillus anthracis

• Characteristics:
• Non-motile, aerobic, encapsulated, non-hemolytic, spore-forming rod
• Very resistant spores: can survive decades in the environment
• Etiological agent of anthrax, predominantly affecting cattle and sheep
• Human infections usually occur through contact with contaminated hides or hair
• Recognized biowarfare agent

Virulence Factors of Bacillus anthracis

• Capsule: Antiphagocytic
• Toxins: Plasmid-encoded
• Protective Antigen (PA)
• Edema Factor (EF)
• Lethal Factor (LF)
• Mechanism of action:

1. PA binds to receptors on host cells (e.g., brain, heart)
2. EF and/or LF binds to PA
3. This complex stimulates endocytosis
4. LF stimulates cytokine release leading to cell death
5. EF acts as an adenylate cyclase, increasing intracellular cAMP levels and causing edema

Epidemiology

• Anthrax is primarily a disease of herbivores
• Human infections arise from exposure to contaminated animals/products
• Rare in the U.S. due to vaccination of livestock
• Severe problems in certain other countries (notably Africa)
• Often utilized as a bioweapon

Clinical Disease

1. Cutaneous Anthrax (most common):

• Spores enter through skin cuts, causing painless papules
• Develop into ulcers surrounded by vesicles, leading to necrotic eschar
• Systemic complications can include painful lymphadenopathy and massive edema
• Untreated mortality: ~20%

1. Gastrointestinal Anthrax (rare in humans):

• Caused by ingestion of contaminated raw/undercooked meat
• Upper GI: ulcers, lymphadenopathy, edema, sepsis
• Lower GI: nausea, vomiting, malaise, with rapid progression to systemic disease
• Untreated mortality: 50-100%

1. Inhalation Anthrax (known as wool-sorter’s disease):

• Caused by inhalation of spores during processing of animal hair
• Prolonged latent period (up to 2 months)
• Symptoms: fever, cough, chest pain, leading to severe complications like mediastinal lymphadenopathy
• Untreated mortality: 100%

Laboratory Diagnosis

• Culture: Presence of large numbers in wounds, lymph nodes, blood
• Characteristic long, thin gram-positive rods arranged in chains
• Direct Fluorescent Antibody (DFA) test against capsule
• PCR tests available

Treatment, Prevention, and Control

• Treatment:
• Penicillin, doxycycline, or ciprofloxacin (resistance may occur)
• Prevention:
• Control of animal disease through vaccination
• Proper disposal of carcasses
• Human vaccination involves a filtrate of an avirulent, non-encapsulated strain

Bioterrorism

• Anthrax is considered an ideal bioweapon due to its inhalation route and high mortality rate
• Historical incidents include:
• Sverdlovsk outbreak (79 cases, 68 deaths)
• Aum Shinrikyo cult release in Japan
• 2001 U.S. postal attacks linked to anthrax spores

Other Bacillus Species

• Bacillus cereus: Opportunistic pathogen responsible for foodborne illnesses
• Two forms: vomiting (from rice) and diarrheal (from meat/vegetables)
• Treatment typically supportive

Listeria monocytogenes

• Characteristics: Gram positive, non-spore forming coccobacilli, catalase positive, motile at room temp
• Commonly associated with contaminated food (soft cheeses, raw vegetables)

Virulence Factors

• Intracellular growth within macrophages
• Listeriolysin O: Disrupts lysosomal membranes
• Phospholipase: Assists in evading immune responses

Epidemiology

• Ubiquitous; found in soil, water, and vegetation
• Disease primarily affects the young, elderly, pregnant women, and individuals with immune defects
• Increasing incidence (reported cases in 2014)

Clinical Disease

• Neonatal Disease:
• Early onset: Granulomatosis infantiseptica; high mortality
• Late onset: Meningitis or meningoencephalitis
• Healthy Adults:
• Typically mild, flu-like symptoms, may develop into meningitis
• Severe risk for pregnant women

Pathogenesis

• Process involves oral ingestion, intestinal penetration, and invasion of the bloodstream

Laboratory Diagnosis

• Often shows no organisms in CSF
• Culture on specific media, cold enrichment techniques

Treatment and Prevention

• Penicillin is the first-line; rising resistance noted
• Prevention via avoiding high-risk foods during pregnancy

Erysipelothrix rhusiopathiae

• Characteristics: Gram positive, non-spore forming, microaerophilic with pleomorphic/filamentous shapes

Virulence Factors

• Limited knowledge; includes capsule, hyaluronidase, and neuraminidase

Epidemiology

• Commensal organism in many animals; zoonotic disease primarily affecting those in contact with animals

Clinical Disease

• Erysipeloid: Localized inflammatory skin condition following trauma

Laboratory Diagnosis

• Found in deep tissues, requiring specific culture conditions for growth

Treatment and Prevention

• Treated with penicillin; prevention through occupational safety measures

Corynebacterium

• Characteristics: Gram positive, non-spore forming rods forming palisades

Corynebacterium diphtheriae

• Causes a toxigenic disease of the throat, associated with severe respiratory issues
• Epidemiology: Primarily disease of children; very rare in vaccinated populations

Clinical Disease

• Symptoms can include flu-like symptoms, pseudomembrane formation, and systemic complications

Laboratory Diagnosis

• Clinical diagnosis supported by culture; toxigenic testing can confirm

Treatment and Prevention

• Antitoxin essential for management; prevention through routine vaccination (DTP)