BACTERIAL PATHOGENICITY

• What is the definition of a pathogen?

  Any microorganism that can cause disease.
• How is pathogenicity defined?

  As the ability or property of a microbial species to cause disease.
• What does pathogenesis describe?

  The mechanisms by which a disease develops, progresses, and persists or is resolved.
• What is virulence?

  The degree of pathogenicity within a group of organisms.
• How does pathogenicity differ from virulence?

  Pathogenicity is qualitative, while virulence is quantitative.
• What is the first necessary step for pathogenicity?

  Infection of the host.
• Does infection equate to disease?

  No, as we are all colonized with bacteria.
• What initiates the disease process?

  When certain abnormal situations or conditions are met.
• What are the four major stages a pathogen must achieve to cause disease?

  1. Exposure or contact with a susceptible host.
  2. Adhesion at the portal of entry using adhesion factors.
  3. Invasion resulting in host tissue damage.
  4. Infection through growth and multiplication of the pathogen.
• What are adhesion factors?

  Adhesins found on the surface of certain pathogens that bind to specific receptors on host cells.
• What role does glycocalyx play in pathogenicity?

  It allows cells to adhere to host tissues and medical devices.
• What is involved in the invasion stage of pathogenicity?

  The dissemination of the pathogen throughout local tissues resulting in host tissue damage.
• What does successful infection lead to?

  Growth and multiplication of the pathogen, which can be local, focal, or systemic.
• How do pathogenic bacteria cause disease in human hosts?

  By expressing virulence factors that bind to host cell targets.
• What is the role of virulence factors?

  They facilitate a variety of host responses and aid in the pathogen's entry and attachment.
• How do some pathogens gain entry into a host?

  Via a portal of entry and attaching to the surface of the host’s mucous membrane.
• What happens when some pathogens release exotoxins?

  They can cause disease without further penetration into the host.
• What determines the specificity of some pathogens for certain tissues or organs?

  The presence of specific receptors for bacterial attachment or certain nutrients required by the bacteria.
• What is a characteristic of species like Mycobacterium?

  They can reside within the cells for long-term residence.
• What factors determine virulence?

  Infectivity of the bacteria and the severity of the condition it produces.
• What is the variation in virulence?

  • Virulence is not constant and may undergo spontaneous or induced variation.
  • Enhancement is known as exaltation.
  • Reduction is known as attenuation.
• What is the median infectious dose (ID$_{50}$)?


  The number of pathogen cells required to cause active infection in 50% of inoculated animals.
• What is the median lethal dose (LD$_{50}$)?


  The number of pathogenic cells required to kill 50% of infected animals.
• How is virulence measured?

  Using controlled experiments with laboratory animals.
• What are the three factors that determine the virulence of a strain?

  1. Invasiveness: ability to invade and multiply in tissue.
  2. Toxigenicity: ability to produce toxins that damage host tissues.
  3. Infectivity: ability to initiate and maintain infection in host tissue.
• What is invasiveness?

  The capacity of an organism to invade and multiply in healthy tissue within a susceptible host.
• How do pathogens invade and multiply in host tissue?

  By using chemical/physical components, metabolic products, and enzymes that counteract normal body defenses.
• What are some examples of virulent factors?

  • Adhesins
  • Aggressins
  • Enzymes
  • Capsules
  • Extracellular slime substances
  • Siderophores
  • Plasmids
  • Toxins
• What is the function of adhesins?

  They attach to receptors on the host cell, facilitating colonization.
• What are fimbriae?

  Components of bacteria that function as adhesins for attachment to host cells.
• What is the role of coagulase?

  It accelerates clotting of plasma and helps protect the pathogen from phagocytosis.
• What do leucocidins do?

  They kill leucocytes, preventing phagocytosis.
• What are haemolysins?

  Substances that cause dissolution of red blood cells.
• What is the function of hyaluronidase?

  It increases tissue permeability and helps spread infection.
• What does fibrinolysin do?

  It promotes the spreading of streptococcal lesions by breaking down fibrin barriers.
• What is the role of collagenase?

  It breaks down collagen, which is part of connective tissues.
• What does lecithinase do?

  It causes lysis of red blood cells and other tissue cells.
• What is the function of streptodornase (DNase)?

  It depolymerizes DNA and liquefies purulent exudates.
• What are the types of enzymes produced by pathogenic bacteria?

  1. Hyaluronidase
  2. Fibrinolysin
  3. Coagulase
  4. Leucocidin
  5. Haemolysin
  6. Collagenase
  7. Lecithinase
  8. DNAse
• What is reptolysin S (SLS)?

  It is an oxygen stable hemolysin not considered antigenic.