Question | Answer |
What is a pathogen? | an organism able to cause disease |
virulence | degree of pathogenicity, invasiveness and toxigenicity, and degree and nature of host cell involvement |
What is a virulence factor? | • Pathogenic traits in bacteria are due to the action of genes coding for specific structures and substances |
virulence mechanisms of microorganisms | resistance, production, evasion, induction and adherence |
What is adherence to host cells? | – extracellular bacteria use receptor-mediated attachment to cell surface
- using specific adhesin molecules; may be on structures: pili or fimbriae
– viruses and intracellular bacteria use specific receptors as prelude to entering the cell |
What is invastion of host cells? | • penetrate or be taken up by host cell
• provides access to nutrients (bacteria) and host cell machinery (viruses)
• may help in avoidance of immune response |
production of substances released.... | degradative enzymes and toxins |
What are exotoxins? | secreted into the environment, protein based; highly antigenic, several modes of action, produced by gram positives and gram negatives, very specific |
What are endotoxins? | • LPS in outer membrane of gram negatives….can damage cell directly, pore formation and cytoskeletal modulator. Disrupt cell communication and interfere with internal cell processes |
Siderophores | • iron-binding compounds excreted by pathogens under iron stress
• host actively sequesters iron during infection to limit growth of pathogens |
Host immune response to pathogen | • superantigen
• cross-reacting antibodies
• immune complexes
• inflammation
• endotoxic shock |