microbiology module 7

• Gram-positive rods


  • Medically important genera: Bacillus, Clostridium, Corynebacterium, Listeria, and Gardnerella
• Spore-forming Gram-Positive Bacilli


  • Bacillus
  • Clostridium
• Bacillus


  Aerobic spore-forming gram-positive bacilli
• Clostridium


  Anaerobic spore-forming gram-positive bacilli
• Bacillus species


  • Large, gram-positive, occurring in chains
  • Spore-forming, aerobic, toxin producing
• Bacillus anthracis


  • Large gram-positive rod with square ends, frequently found in chains
  • Antiphagocytic capsule composed of D-glutamate
  • Can produce Anthrax toxin
• Anthrax pathogenesis


  1. Production of anthrax toxin

  2. Primarily a zoonotic disease

  3. May present as cutaneous, pulmonary (inhalation), and gastrointestinal
• Anthrax transmission


  • Cutaneous: Spores enter wound
  • Pulmonary: Spores are inhaled
  • Gastrointestinal: Ingestion of contaminated meat
• Bacillus cereus


  • Pathogenesis is due to the action of enterotoxins
  • Causes food poisoning
• Bacillus cereus food poisoning


  • Short incubation period (4 hours): nausea, vomiting
  • Long incubation period (18 hours): watery, nonbloody diarrhea
• Clostridium species


  • Anaerobic, spore-forming, gram-positive rods
  • Medically important species: Clostridium tetani, Clostridium botulinum, Clostridium perfringens and Clostridium difficile
• Clostridium tetani


  • Produces a terminal spore
  • Pathogenesis is due to the action of tetanospasmin
• Clostridium tetani (Tetanus)


  1. Spores enter wound site

  2. Strong muscle spasms (spastic paralysis, tetany) (eg, lockjaw, risus sardonicus, opisthotonos, spastic paralysis)
• Clostridium botulinum


  • Pathogenesis is due to the action of the botulinum toxin
  • Blocks release of acetylcholine at peripheral nerve synapses
• Clostridium botulinum (Botulism)


  1. Ingestion of spores/preformed toxin; contamination of wound

  2. Descending weakness and paralysis of cranial nerves (ie, diplopia, dysphagia, ptosis, and respiratory muscle failure)
• Clostridium perfringens


  Causes two distinct diseases: gas gangrene and food poisoning
• Clostridium perfringens gas gangrene


  Due to α-toxin (lecithinase); characterized by pain, edema, cellulitis, necrosis, soft tissue crepitus, hemolysis, jaundice
• Clostridium perfringens food poisoning

  1. 16-hour incubation period; watery diarrhea with cramps and little vomiting which resolves in 24 hours
• Clostridium difficile


  • Antibiotic-associated pseudomembranous colitis
  • Pathogenesis: Antibiotics suppress drug-sensitive members of the normal flora of the colon, allowing C. difficile to multiply and produce large amounts of exotoxins A and B
• Clostridium difficile pseudomembranous colitis


  Diarrhea associated with pseudomembranes (yellow-white plaques) on the colonic mucosa
• Corynebacterium diphtheriae


  • Gram-positive rods that appear club-shaped (wider at one end); are arranged in palisades or in V- or L-shaped formations
  • Causes diphtheria
• Corynebacterium diphtheriae diphtheria toxin

  Inhibits protein synthesis by ADP-ribosylation of elongation factor-2 (EF-2)
• Corynebacterium diphtheriae (Diphtheria)


  1. Thick, gray, adherent pseudomembrane over the tonsils and throat; fever, sore throat, and cervical adenopathy; ulcerating skin lesions covered by a gray membrane (cutaneous)

  2. Complications: airway obstruction, myocarditis, nerve weakness/paralysis (cranial nerves)
• Listeria monocytogenes


  • Gram-positive rods that exhibit tumbling motility
  • Causes meningitis and sepsis in newborns, pregnant women, and immunosuppressed adults; febrile gastroenteritis
• Listeria monocytogenes (Listeriosis)


  1. Transmission: ingestion of unpasteurized milk products, undercooked meat, and raw vegetables

  2. Meningitis, Sepsis

  3. Gastroenteritis: watery diarrhea, fever, headache, myalgias, and abdominal cramps but little vomiting
• Gardnerella vaginalis


  • Small, facultative, gram-variable rod
  • Causative agent in Bacterial Vaginosis
• Gardnerella vaginalis (Bacterial Vaginosis)


  Malodorous, white or gray-colored vaginal discharge with "fishy" odor