infection

• successful clinically important microorganisms must leave the body or host and then be transmitted to new hosts
• what does transmission of infection depend on?

  1. number of microbes being shed
  2. the ability of the micro-organism to survive in the environment or vector
  3. the number of micro-organisms required to infect a new host (efficiency of infection)
• production of leucocidins 


  kill WBC
• production of haemolysins


  kill RBC
• production of Exotoxin A

  inhibits protein synthesis
• low levels of LPS

  moderate immune response, moderate cytokine production, moderate inflammation and fever, pathogen effectively cleared
• LPS are components found on the outer membrane of gram negative bacteria 


  they are released during bacterial infections or when bacteria is destroyed
• what might you expect if large amounts of LPS are released into the bloodstream?

  triggers an immune response which can lead to sepsis, endotoxin shock, DIC, multiple organ failure
• gram positive shock triggered by teichoic acids and lipoteichoic acids
• exotoxins

  soluble polypeptide molecules secreted by bacteria or released following cell lysis
• superantigens

  secreted proteins (exotoxins) non-specific activation of T cells resulting in polyclonal T cell activation and massive cytokine release, ex: toxic shock toxin / s. aureus
• bacteria adhere to host tissue to establish a focus for infection. they do this by means of pili, adhesions, and the ability to form biofilms
• adherent bacteria can invade tissues and cells if opportunity arises ex: invasins
• bacteria can produce a variety of proteins / carbohydrates that allow them to avoid the immune response ex: anti-phagocytic and anti-lytic agents
• during the invasion process, bacteria can damage host cells by a variety of mechanisms ex: toxins and enzymes