Microbial Mechanisms of Pathogenicity
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint ® Lecture Slide Presentation prepared by Christine L. Case M I C R O B I O L O G Y a n i n t r o d u c t i o n ninth edition TORTORA FUNKE CASE 15 Microbial Mechanisms of Pathogenicit y
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Transcript of Microbial Mechanisms of Pathogenicity
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
PowerPoint® Lecture Slide Presentation prepared by Christine L. Case
M I C R O B I O L O G Ya n i n t r o d u c t i o n
ninth edition TORTORA FUNKE CASE
15Microbial
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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Portal of Entry ID50
Skin 10-50 endospores
Inhalation 10,000-20,000 endospores
Ingestion 250,000-1,000,000 endospores
Bacillus Anthracis
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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.
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.
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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
Endotoxins
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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
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Exotoxins
A-B toxins
Figure 15.5
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Exotoxins
Membrane-disrupting toxins
Lyse host’s cells by
Making protein channels in the plasma membrane
(e.g., leukocidins, hemolysins).
Disrupting phospholipid bilayer.
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Exotoxins
Superantigens
Cause an intense immune response due to release
of cytokines from host cells.
Fever, nausea, vomiting, diarrhea, shock, and death.
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Exotoxins
Specific for a structure or function in host cell
Figure 15.4a
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Exotoxins
ExotoxinLysogenic conversion
Corynebacterium diphtheriaeA-B toxin.
Inhibits protein synthesis.+
Streptococcus pyogenesMembrane-disrupting.
Erythrogenic.+
Clostridium botulinum A-B toxin. Neurotoxin +
C. tetani A-B toxin. Neurotoxin
Vibrio cholerae A-B toxin. Enterotoxin +
Staphylococcus aureus Superantigen. +
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Endotoxins
Figure 15.6
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Cytopathic Effects of Viruses
Table 15.4
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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
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Pathogenic Properties of Fungi
Aflatoxin
Aspergillus
Mycotoxins
Neurotoxins: Phalloidin, amanitin
Amanita
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Pathogenic Properties of Protozoa
Presence of protozoa.
Protozoan waste products may cause symptoms.
Avoid host defenses by
Growing in phagocytes
Antigenic variation
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Pathogenic Properties of Helminths
Use host tissue.
Presence of parasite interferes with host function.
Parasite's metabolic waste can cause symptoms.
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Pathogenic Properties of Algae
Paralytic shellfish poisoning
Dinoflagellates
Domoic acid intoxication
Diatoms
Figure 27.15
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Portals of Exit
Respiratory tract
Coughing and sneezing
Gastrointestinal tract
Feces and saliva
Genitourinary tract
Urine and vaginal secretions
Skin
Blood
Biting arthropods and needles or syringes
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Mechanisms of Pathogenicity
Figure 15.9
