Clostridium species


  • Clostridia produce the largest number of toxins of any bacterial class.
  • The common source of entry in humans is the gastrointestinal tract or trauma.
  • Obligate anaerobic bacteria with unusual features: spore formation, toxin production and normally reside in the environment or the gastrointestinal tract of humans and animals. Dominant form in the human intestinal flora.
  • Belongs to phylum Firmicutes, which is the dominant component of the fecal microbiome. Clostridia spp. account for 50% or about 1013/gm stool.
  • Species-specific toxin expression:
    • Botulism (C. botulinum)
    • Colitis (C. difficile)
    • Tetanus (C. tetani)
    • Septic abortion (C. sordellii, now referred to as Paeniclostridium sordellii)
      • The organism is prevalent among goats, horses, and sheep.
      • Organism also described as causing soft-tissue infections.
    • Gas gangrene (C. perfringens, C. novyi, C. septicum, P. sordellii, C. histolyticum)
    • Clostridial food poisoning (C. perfringens)
  • Non-toxigenic strains are often components of mixed infections or bacteremia; their pathogenic role is often unclear.
Clostridia + Clostridial toxins*




Gastrointestinal tract

  • C. perfringens


Food intoxication, diarrhea, sudden infant death

Beta toxin

Necrotic enteritis

  • Clostridioides (ex. Clostridium) difficile

Ted A + Ted B

Antibiotic-associated diarrhea + colitis

  • C. septicum


Intestinal myonecrosis

  • C. botulinum

BoNT/A, B, E

Human botulism

Wound-related diseases

  • C. perfringens

Alpha toxin

Gangrene, puerperal sepsis

  • Paeniclostridium sordellii (ex. Clostridia sordellii)

Tcsl, Tcstl


  • C. tetani



  • C. novyi



  • C. botulinum

BoNT/A + B

Wound botulism

* Adapted from Popoff MR, Bouvel P; Future Microbio 2009; 4: 1021

TeNT - Tetanus toxin; BoNT - Botulinum neurotoxin; TcsH - C. sordellii hemorrhagic toxic; TcsL - C. sordellii lethal toxin; TcdA, alpha-toxin; TedB - Beta toxin

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Last updated: October 6, 2023