Parasites II

• Endospores


  Dehydrated multi-shelled structure that allows bacteria to survive environmental assaults that would normally kill the bacterium e.g. high temperature, desiccation, chemical damage, enzymatic destruction
• Endospore formation


  Allows bacteria to exist in a 'hibernating' state during unfavourable conditions
• Endospores


  • Contain a complete copy of the chromosome, some essential proteins and ribosomes
  • Vary in size and location within the cell
• Endospores provide resistance against drying, low nutrient conditions, radiation, high temperatures, and various chemical disinfectants
• Endospores can germinate into single bacteria when conditions become favourable for growth again
• Endospore formation is not a form of reproduction
• Spore-forming bacteria


  • A few genera of bacteria produce endospores, such as Clostridium and Bacillus, both of which are Gram-positive rods
  • Endospore production is associated with Gram-positive bacteria
• Schaeffer-Fulton Staining Procedure


  Used to differentiate between endospores (stained with malachite green) and vegetative cells (stained with safranin counterstain)
• Pathogenic spore-forming Gram-positive bacteria

  • Bacillus anthracis (anthrax)
  • Clostridium botulinum (botulism)
  • Clostridium perfringens (gas gangrene)
  • Clostridium tetani (tetanus)
• Bacillus anthracis


  • Facultative anaerobe
  • Bacilli that occur singly, in pairs, or in chains
  • Form highly resilient endospores
  • Pathogenic strains produce lethal anthrax toxins
  • Lives in the soil (likes alkaline rich soil)
  • Spores lose capsule and germinate inside animals
  • Toxins disrupt blood capillaries permeability, causing them to leak and blood cannot clot
• Transmission of Bacillus anthracis

  1. Inoculation of spores through break in the skin (cutaneous)

  2. Ingestion of spores (intestinal)

  3. Inhalation of spores (respiratory, most lethal for humans)
• Cutaneous anthrax


  Produces ulcer called an eschar, fatal in untreated patients
• Gastrointestinal anthrax


  Rare in humans
• Inhalation anthrax


  Rare in humans (wool-sorters' disease), requires inhalation of airborne endospores, high mortality rate
• Diagnosis of Bacillus anthracis


  1. Observation of large, non-motile, Gram-positive bacilli in lung, blood or skin samples

  2. Chest X-ray or CT scan

  3. PCR and Real-Time PCR

  4. Antigen detection
• Treatment of Bacillus anthracis

  • Many antimicrobials are effective, e.g. Penicillin, or ciprofloxin
  • Effective vaccine available (requires multiple doses and boosters)
• Clostridium


  • Anaerobic, endospore-forming bacillus
  • Ubiquitous in soil, water, and gastrointestinal tracts of animals and humans
• Clostridium perfringens


  • Large, rod-shaped, non-motile, anaerobic bacillus
  • Clostridium most frequently isolated from clinical specimens
  • Produces toxins that can cause irreversible damage to body
  • Grows in the digestive tracts of animals and humans
  • Spores wider than bacillus body
• Clostridium perfringens diseases


  • Food poisoning (abdominal cramps and watery diarrhoea)
  • Gas gangrene (trauma introduces endospores into body, endospores germinate and cause necrosis and oedema)
• Diagnosis of Clostridium perfringens

  1. Presence of minimum bacterial load in food or faeces

  2. Stormy fermentation in Litmus milk

  3. Target haemolysis on blood agar

  4. Appearance of gas gangrene is usually diagnostic
• Treatment of Clostridium perfringens

  • Food poisoning is self-limited
  • Gas gangrene requires removal of dead tissue and administration of anti-toxin and penicillin
• Prevention of Clostridium perfringens


  • Refrigeration of foods can reduce cases of food poisoning
  • Proper cleaning of wounds can prevent gas gangrene
• Clostridium difficile


  • Common member of the intestinal microbiota, motile and anaerobic
  • Opportunistic pathogen in patients taking broad-spectrum antimicrobial drugs
  • Produces two toxins and the enzyme hyaluronidase
• Clostridium difficile disease


  • Minor infections result in self-limiting explosive diarrhoea
  • Serious cases can cause pseudomembranous colitis, where sections of the colon wall slough off, causing massive infection by faecal bacteria - life-threatening condition
• Diagnosis of Clostridium difficile

  1. Isolation of organism or detection of toxins in faeces

  2. Demonstrate the presence of toxins by enzyme immunoassay (false positives)

  3. PCR to rapidly detect toxin B gene – highly accurate

  4. Cell cytotoxicity assay – effects of toxins on cells in culture – sensitive, but less widely available
• Treatment of Clostridium difficile


  • Discontinue causative antimicrobial drug to resolve minor infections
  • Serious cases treated with antibiotics, e.g. metronidazole
• Prevention of Clostridium difficile


  Proper hygiene to limit nosocomial infections
• Clostridium tetani


  • Motile, obligate anaerobic bacilli with a terminal endospore
  • Ubiquitous in soil, dust and gastrointestinal tract of animals and humans
• Tetanus pathogenesis


  • Tetanospasmin toxin (tetanus toxin) released by C. tetani cells when they die
  • Potent neurotoxin that blocks release of inhibitory neurotransmitter, causing continuous muscle contraction
• Tetanus disease


  • Initial tightening of the jaw and neck muscles, commonly called lockjaw
  • Spasms and contractions can spread to other muscles
  • Unrelenting contraction of the diaphragm can cause death
  • Most cases occur in less-developed countries (inadequate medical care and lack of vaccination)
  • Mortality rate about 50%
• Diagnosis and treatment of tetanus

  1. Characteristic muscular contraction

  2. Cleansing of wounds to remove endospores

  3. Administer immunoglobulin against tetanus toxin

  4. Administer antimicrobial drugs

  5. Active immunisation with tetanus toxoid
• Prevention of tetanus is through immunisation with tetanus toxoid