Microbial Mechanisms of Pathogenicity

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Microbial Mechanisms of Pathogenicity
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Microbial Mechanisms of Pathogenicity

• Pathogenicity The ability to cause disease
• Virulence The extent of pathogenicity

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Portals of Entry

• Mucous membranes
• Skin
• Parenteral route

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Numbers of Invading Microbes

• ID50 Infectious dose for 50 of the test
  population
• LD50 Lethal dose (of a toxin) for 50 of the
  test population

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Bacillus anthracis
Portal of entry ID50
Skin 10-50 endospores
Inhalation 10,000-20,000 endospores
Ingestion 250,000-1,000,000 endospores
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Adherence

• Adhesions/ligands bind to receptors on host cells
• Glycocalyx Streptococcus mutans
• Fimbriae Escherichia coli
• M protein Streptococcus pyogenes
• Opa protein Neisseria gonorrhoeae
• Tapered end Treponema pallidum

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Enzymes

• Coagulase Coagulate blood
• Kinases Digest fibrin clots
• Hyaluronidase Hydrolyses hyaluronic acid
• Collagenase Hydrolyzes collagen
• IgA proteases Destroy IgA antibodies
• Siderophores Take iron from host
  iron- binding proteins
• Antigenic variation Alter surface proteins

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Penetration into the Host Cell
Figure 15.2
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Toxins

• Toxin Substances that contribute to
  pathogenicity
• Toxoid Inactivated toxin used in a vaccine
• Antitoxin Antibodies against a specific toxin

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Endotoxin
Figure 15.4b
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Exotoxin

Source Mostly Gram
Metabolic product By-products of growing cell
Chemistry Protein
Fever? No
Neutralized by antitoxin Yes
LD50 Small