Clostridium Bacteria and Gas Gangrene

Clostridium

• Clostridia are spore-forming bacteria found in soil and the intestines of animals and humans
• Many species are saprophytes
• Some species cause diseases like gas gangrene, tetanus, botulism, and pseudomembranous colitis
• Morphology: Large, gram-positive rod bacteria (1µm thick, 3-8µm long)
• Gram-negative reaction seen in some older cultures
• Flagellated, except for C. perfringens

Gas Gangrene Pathogens

• The most frequent causative pathogen is Clostridium perfringens
• Toxins produced: Necrotizing, hemolytic, and lethal
• Enzymes produced: Collagenases, proteinases, DNases, lecithinases, and hyaluronidase
• These enzymes destroy tissue structures, leading to accumulation of toxic metabolites.

Pathogenesis and Clinical Picture

• Anaerobic Cellulitis: Infection confined to fascial spaces, no muscle involvement, cracking of skin (crepitus), no toxemia
• Gas Gangrene (Clostridial Myonecrosis): Aggressive infection of muscles, myonecrosis (tissue death), and toxemia

Clostridium Tetani (Tetanus)

• Acute clostridial disease
• Toxin: Tetanospasmin (neurotoxin composed of two polypeptide chains linked by a disulfide bridge)
• Pathogenesis: Heavy chain binds to neuron receptors while the light chain is a zinc-metalloprotease that causes proteolysis of neuroexocytosis components. This blocks transmission of inhibitory impulses to motor end plates.
• Symptoms: Increased muscle tone and spasms triggered by stimuli (visual or acoustic).
• Treatment: Antitoxic therapy with immune sera following wound cleaning

Clostridium Botulinum (Botulism)

• Foodborne botulism: Toxin ingested with food
• Infant botulism: Spores ingested by infants. Wound botulism: Infection from wound.
• Botulinum toxin (neurotoxin): Heat-labile protein; seven toxigenic types
• Pathogenesis: Types A, B, and E cause human poisoning that results in the production of the toxin under anaerobic conditions.
• Symptoms: Difficulty speaking, swallowing, constipation, dry mucosa, and muscle weakness progressing to respiratory paralysis.

Clostridium Difficile (Pseudomembranous Colitis)

• C. difficile occurs in the fecal flora of 1–4% of healthy adults and in 30–50% of children under one year of age.
• Pathogenesis: Two toxins produced; Toxin A (enterotoxin causing electrolyte and fluid secretion) and Toxin B (cytotoxin damaging colon mucosa)
• Symptoms: Fever, diarrhea, and spasmodic abdominal pain
• Treatment: Antibiotic treatment indicated in severe cases (metronidazole is agent of choice)