1. Chapter 15 Microbial Mechanisms of Pathogenicity
Biology 205
Chandler-Gilbert Community College

2. Microbial Mechanisms of Pathogenicity
Pathogenicity: The ability to cause disease.
Virulence: The extent of pathogenicity.

3. Portals of Entry
Mucous membranes
Skin
Parenteral route

4. 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.

5. Bacillus Anthracis Portal of Entry ID50 Skin 10-50 endospores
Inhalation
10,000-20,000 endospores
Ingestion
250,000-1,000,000 endospores

6. 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

7. 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

8. Penetration into the Host Cell
Figure 15.2

9. Toxins Toxin: Substances that contribute to pathogenicity.
Toxigenicity: Ability to produce a toxin.
Toxemia: Presence of toxin in the host's blood.
Toxoid: Inactivated toxin used in a vaccine.
Antitoxin: Antibodies against a specific toxin.

10. Present in LPS of outer membrane
Endotoxins
Source:
Gram –
Relation to microbe:
Present in LPS of outer membrane
Chemistry:
Lipid
Fever?
Yes
Neutralized by antitoxin? No
LD50:
Relatively large
Figure 15.4b

11. By-products of growing cell
Exotoxin
Source:
Mostly Gram +
Relation to microbe:
By-products of growing cell
Chemistry:
Protein
Fever? No
Neutralized by antitoxin?
Yes
LD50:
Small
Figure 15.4a

12. Exotoxins
A-B toxins
Figure 15.5

13. Exotoxins Membrane-disrupting toxins Lyse host’s cells by
Making protein channels in the plasma membrane (e.g., leukocidins, hemolysins).
Disrupting phospholipid bilayer.

14. Exotoxins Superantigens
Cause an intense immune response due to release of cytokines from host cells.
Fever, nausea, vomiting, diarrhea, shock, and death.

15. Exotoxins Specific for a structure or function in host cell
Figure 15.4a

16. Exotoxins Exotoxin Corynebacterium diphtheriae
Lysogenic conversion
Corynebacterium diphtheriae
A-B toxin. Inhibits protein synthesis. +
Streptococcus pyogenes
Membrane-disrupting. Erythrogenic.
Clostridium botulinum
A-B toxin. Neurotoxin
C. tetani
Vibrio cholerae
A-B toxin. Enterotoxin
Staphylococcus aureus
Superantigen.

17. Endotoxins
Figure 15.6

18. Cytopathic Effects of Viruses
Table 15.4

19. Pathogenic Properties of Fungi
Fungal waste products may cause symptoms.
Chronic infections provoke an allergic response.
Tichothecene toxins inhibit protein synthesis.
Fusarium
Proteases
Candida, Trichophyton
Capsule prevents phagocytosis.
Cryptococcus
Ergot toxin
Claviceps

20. Pathogenic Properties of Fungi
Aflatoxin
Aspergillus
Mycotoxins
Neurotoxins: Phalloidin, amanitin
Amanita

21. Pathogenic Properties of Protozoa
Presence of protozoa.
Protozoan waste products may cause symptoms.
Avoid host defenses by
Growing in phagocytes
Antigenic variation

22. Pathogenic Properties of Helminths
Use host tissue.
Presence of parasite interferes with host function.
Parasite's metabolic waste can cause symptoms.

23. Pathogenic Properties of Algae
Paralytic shellfish poisoning
Dinoflagellates
Domoic acid intoxication
Diatoms

24. Portals of Exit Respiratory tract Gastrointestinal tract
Coughing and sneezing
Gastrointestinal tract
Feces and saliva
Genitourinary tract
Urine and vaginal secretions
Skin
Blood
Biting arthropods and needles or syringes

25. Mechanisms of Pathogenicity
Figure 15.9