CLINICAL BACTERIOLOGY

• Anaerobes


  Organisms that do not grow in the presence of oxygen (O2)
• Obligate or strict anaerobes


  • 0% O2
  • Killed upon brief exposure, less than a few minutes to atmospheric oxygen
  • Unable to protect themselves against the action of oxygen
• Anaerobes


  • Require an environment free of oxygen in order for them to survive and grow
• Other types of organisms

  • Capnophilic - requires carbon dioxide (CO2) concentration of 5% to 10%
  • Microaerophilic - grow in an oxygen (O2) concentration of 5% or less
  • Facultative Anaerobes - grow in the presence of oxygen (O2)
  • Obligate or Strict Anaerobes - do not grow in the presence of oxygen (O2), they can get killed almost instantly in the presence of oxygen
  • Aerotolerant or Moderate Anaerobes - can survive short exposure to oxygen (O2) but will not be able to perform metabolic processes unless placed in an anaerobic environment
• Molecular oxygen is toxic to obligate or strict anaerobes
• Oxygen reduction during cellular metabolism

  1. O2 + e- O2 (superoxide anion)

  2. O2 + e- 2H+ H2O2 (hydrogen peroxide)
• Superoxide anion reacts with hydrogen peroxide in the presence of iron to generate hydroxyl radical
• Reaction between hydroxyl radical and superoxide anion forms singlet oxygen which is also damaging to cells
• Superoxide dismutase


  Enzyme that converts superoxide anion to oxygen and hydrogen peroxide
• Catalase


  Enzyme that breaks down hydrogen peroxide into oxygen and water
• Anaerobes lack superoxide dismutase and/or catalase, making them susceptible to oxygen derivatives
• Where anaerobes are found

  • Soil
  • Freshwater
  • Saltwater sediments
  • Components of the endogenous microbiota (normal flora) of humans and other animals
  • Found in the environment (exogenous anaerobes)
• Exogenous anaerobic infections


  Usually caused by gram-positive, spore-forming bacilli belonging to the genus Clostridium
• Clostridium perfringens


  Gram-positive bacilli that appear as purple "boxcar" shaped rods when gram stained
• Clostridium perfringens colonies


  • Large, white with double zone of beta-hemolysis
• Diseases caused by Clostridium perfringens

  • Food poisoning
  • Gas Gangrene/Myonecrosis
  • Bacteremia
• Clostridium botulinum


  Gram-positive rod, anaerobic bacilli that causes botulism
• Botulinum toxin


  • Extremely potent neurotoxin
  • Prevents release of acetylcholine, resulting in flaccid paralysis and death
• Types of botulism


  • Foodborne botulism
  • Infant botulism
  • Wound botulism
• Botulinum toxin and Clostridium botulinum are considered potential bioterrorism agents
• Clostridium tetani


  Causes tetanus, has a terminal spore giving it a "tennis racket" or "drumstick" shape

  
• Mechanism of action of tetanus toxin

  1. Tetanospasmin (tetanus toxin) enters the inhibitory neuron called Renshaw cells

  2. Tetanospasmin blocks the release of inhibitory neurotransmitters from Renshaw cells

  3. This leads to unopposed contraction of skeletal muscles, causing tetanic spasms

  
• Antitoxin


  Treatment of foodborne botulism
• Supportive Care


  Treatment of foodborne botulism
• CLOSTRIDIUM TETANI


  • Tennis racket or drumstick-shaped due to the terminal spore
• Mechanism of action (Tetanus toxin)

  1. Tetanospasmin enters inhibitory neuron called renshaw cells

  2. Tetanospasmin cleaves smear proteins, preventing release of inhibitory neurotransmitters

  3. Alpha neurotransmitters keep stimulating muscle causing continuous muscular spasm

  
• Tetanus


  • Caused by C. tetani
  • Occurs when spores in the environment enter the skin through puncture wounds
  • Tetanospasmin is the neurotoxin produced by C. tetani

  
• Symptoms usually appear approximately 7 days after the injury
• Incubation period


  1. 21 days, length related to distance from injury to central nervous system
• Tetanus triad


  • Trismus (Lockjaw)
  • Risus sardonicus (distorted grin)
  • Opisthotonus (Severe muscle spasm resulting in arch back)
• Muscle spasms in the Pharyngeal area Results to difficulty in swallowing
• Reflex spasm Develops on most patients with tetanus and minimal external stimuli such as noise, touch, or light

  
• Vaccine


  Tetanus, Diphtheria, Pertussis (Tdap) Vaccine
• CLOSTRIDIUM SEPTICUM


  • Can cause myonecrosis and bacteremia
  • Often a marker organism for a malignancy in the GI tract (if it is in the blood stream)
• CLOSTRIDIUM DIFFICILE


  • Part of GI biota in about 5% of individuals
  • Most common cause of antibiotic-associated diarrhoea and Pseudomonas colitis
• Antimicrobial Therapy


  Many bowel biota organisms other that C. difficile are killed, thus allowing C. difficile to multiply with less competition and produce high levels of two toxins
• Prolonged use of antibiotic


  Can kill the normal flora of the GI tract, allowing C. difficile to proliferate
• Toxin A (C. difficile)

  Enterotoxin, weakly cytopathic toxin, predominantly responsible for the enterotoxic activity
• Toxin B (C. difficile)


  Potent cytotoxin
• Pseudomembranous colitis


  When the surface of the inflamed bowel is overlaid with Pseudomembrane composed of necrotic debris and WBCs