M4: topic 2

• Pathogenicity


  Ability of a parasite to inflict damage to host
• Virulence


  • Measure of pathogenicity
  • Availability of nutrients which affects growth
  • Pathogens must multiply and colonise the tissue (initial inoculum doesn't affect the host)
• Things for risk of infectious disease


  • Host which needs to be susceptible
  • Agent: pathogen, virulence, dosage and type
  • Environment: conditions, season, population and source
• Infection


  • When micro-organisms is established and growing in host
  • Pathogen replicates and grows inside a host
• Chronic infection


  New pathogens emerge with no resistance
• Types of microbe-related infections


  • Bacteremia: bacteria in the blood stream
  • Septicemia: blood borne systematic infection which = inflammation and death
• Stages of microbes which = disease


  1. Gain entry – exposure

  2. Attachment – adherence

  3. Invade specific tissue or cells – invasion

  4. Evade defence – infection

  5. Obtain nutrients

  6. Exit host
• Types of infection


  • Toxicity: toxin effects are local or systemic
  • Invasiveness: further growth at original and distant sites
• Virulence factors used by pathogens


  • Combination of toxins, attachment, invasiveness and resistance to increase pathogenicity
• Toxins


  • Inhibits host cell function
  • Travel to other sites
• Attachment


  • To surface as well as growth
  • Fimbrae and pilli
  • Receptors determine type of cell it attaches to
• Invasiveness


  Grow in tissue to inhibit function
• Biofilms


  • Extra-cellular molecules attach to bacterial surface and often persistent infection
  • Release acyl-homoserine lactone "AHL" to regulate genes
• Steps for biofilm formation


  1. Attachment

  2. Colonisation

  3. Development

  4. Active dispersal
• Common infections from biofilms


  • Chronic infection
  • Otitis media: ear infection
  • Endocarditis
  • Legionnaires
  • UTI
• Endotoxin


  • Gram negative cell wall
  • Heat stable
  • Has lipopolysaccharides proportion of the cell envelope = heat
  • O-antigens found and targets immune response
  • Action: fever, diarrhea and vomiting
  • No toxic potential
• Exotoxin


  • Gram negative and positive
  • Decreased by heat and chemicals
  • Highly toxic
  • Has proteins
  • In bacteria
  • No fever
  • Action: specific to receptor
• Steps of endotoxin action


  1. Macrophage integrates with gram -ve

  2. Bacterium degrades = release endotoxin

  3. Cytokines released in bloodstream by macrophages

  4. Cytokines induce hypothalamus = prostaglandins
• Enterotoxins


  • Exotoxins that affect the intestine
  • Massive secretion of fluid into lumen
• Types of exotoxins


  • Cytolytic toxins: degrades cyto membrane = cell lysis
  • Superantigens: increase the number of immune cells
  • AB toxins: b subunits bind to host cell receptors = transfer of damage agents across membrane
• Types of AB toxins


  • Botulinum: blocks acetylcholine receptors = relax muscles
  • Tetanus: prevents glycine from inhibitory interneurons = muscles contract
• Virulence factors for Salmonella


  • Pathogenicity island on chromosome
  • Plasmid
  • Exoenzyme
  • Toxins
  • Block phagocyte response = capsule
  • Fimbrae