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BACTERIA · Gram-positive spore-forming anaerobic rod

Clostridioides (Clostridium) difficile

Clostridioides difficile — Gram stain

Stain: Gram stainMorphology: Gram-positive bacilli (purple rods) often with subterminal/terminal sporesYield: HIGHDifficulty: EASY
Clostridioides (Clostridium) difficile microscopic image — Gram-positive spore-forming anaerobic rod, Gram stain
Image: Wikimedia Commons · File:Clostridium_difficile_gram_stain.jpg (CC BY-SA 4.0)

Key facts

**Pathogenesis**: Antibiotic disruption of gut flora allows overgrowth. Toxin A (enterotoxin) and Toxin B (cytotoxin) glucosylate Rho GTPases → cytoskeletal disruption → pseudomembrane formation. **Diagnostic clue**: Watery diarrhea, leukocytosis, recent antibiotic exposure (clindamycin, fluoroquinolones, cephalosporins, PPIs). PCR/NAAT for toxin genes + EIA. **Virulence**: Spore-forming (alcohol-resistant — use soap & water and bleach), toxins A/B; hypervirulent NAP1/BI/027.

Boards buzzwords

  • pseudomembranous colitis
  • toxins A and B
  • antibiotic-associated diarrhea
  • clindamycin/fluoroquinolone exposure
  • yellow plaques on colonoscopy

Associated diseases

  • Antibiotic-associated diarrhea
  • Pseudomembranous colitis
  • Toxic megacolon
  • Recurrent C. difficile infection

Treatment

Oral vancomycin OR fidaxomicin first-line; IV metronidazole only if oral route unavailable; FMT for multiple recurrences

Related organisms

Listeria monocytogenes
Listeria monocytogenes
Gram-positive rod (facultative intracellular)
Mycobacterium tuberculosis
Mycobacterium tuberculosis
Acid-fast bacillus (mycolic acid cell wall)
Nocardia spp.
Nocardia spp.
Gram-positive filamentous, partially acid-fast
Treponema pallidum
Treponema pallidum
Spirochete
Mycobacterium leprae
Mycobacterium leprae
Acid-fast bacillus (obligate intracellular)
Neisseria meningitidis
Neisseria meningitidis
Gram-negative diplococci