1. Microbial Mechanisms of Pathogenicity

2. PathogenicityThe ability to cause disease PathogenicityThe ability to cause disease VirulenceThe extent of pathogenicity VirulenceThe extent of pathogenicity

3. Mucous membranes Mucous membranes Skin Skin Parenteral route Parenteral route Portals of Entry

4. ID 50 : Infectious dose for 50% of the test population ID 50 : Infectious dose for 50% of the test population LD 50 : Lethal dose (of a toxin) for 50% of the test population LD 50 : Lethal dose (of a toxin) for 50% of the test population Numbers of Invading Microbes

5. Bacillus anthracis Portal of entry ID 50 Skin 10-50 endospores Inhalation 10,000-20,000 endospores Ingestion 250,000-1,000,000 endospores

6. Adhesions/ligands bind to receptors on host cells Adhesions/ligands bind to receptors on host cells GlycocalyxStreptococcus mutans GlycocalyxStreptococcus mutans FimbriaeEscherichia coli FimbriaeEscherichia coli M proteinStreptococcus pyogenes M proteinStreptococcus pyogenes Opa proteinNeisseria gonorrhoeae Opa proteinNeisseria gonorrhoeae Tapered endTreponema pallidum Tapered endTreponema pallidum Adherence

7. CoagulaseCoagulate blood CoagulaseCoagulate blood KinasesDigest fibrin clots KinasesDigest fibrin clots HyaluronidaseHydrolyses hyaluronic acid HyaluronidaseHydrolyses hyaluronic acid CollagenaseHydrolyzes collagen CollagenaseHydrolyzes collagen IgA proteasesDestroy IgA antibodies IgA proteasesDestroy IgA antibodies SiderophoresTake iron from host iron- binding proteins SiderophoresTake iron from host iron- binding proteins Antigenic variationAlter surface proteins Antigenic variationAlter surface proteins Enzymes

8. Penetration into the Host Cell Figure 15.2

9. Toxins ToxinSubstances that contribute to pathogenicity ToxinSubstances that contribute to pathogenicity ToxoidInactivated toxin used in a vaccine ToxoidInactivated toxin used in a vaccine AntitoxinAntibodies against a specific toxin AntitoxinAntibodies against a specific toxin

10. Endotoxin Figure 15.4b

11. ExotoxinSource Mostly Gram + Metabolic product By-products of growing cell ChemistryProtein Fever?No Neutralized by antitoxin Yes LD 50 Small