chapter 15 microbial mechanisms of pathogenicity biology 205 chandler-gilbert community college
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Chapter 15Chapter 15Microbial Microbial
MechanismsMechanismsof Pathogenicityof Pathogenicity
Biology 205Biology 205
Chandler-Gilbert Community CollegeChandler-Gilbert Community College
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Microbial Mechanisms of Microbial Mechanisms of PathogenicityPathogenicity
PathogenicityPathogenicity: The ability to cause disease.
VirulenceVirulence: The extent of pathogenicity.
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Portals of EntryPortals of Entry
Mucous membranesMucous membranes SkinSkin Parenteral routeParenteral route
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Numbers of Invading Numbers of Invading MicrobesMicrobes
ID50: Infectious doseInfectious dose for 50% of the test population.
LD50: Lethal doseLethal 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 AnthracisBacillus Anthracis
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AdherenceAdherence
Adhesions/ligands bind to receptors on host cells GlycocalyxGlycocalyx: Streptococcus mutans FimbriaeFimbriae: Escherichia coli M proteinM protein: Streptococcus pyogenes Opa proteinOpa protein: Neisseria gonorrhoeae Tapered endTapered end: Treponema pallidum
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EnzymesEnzymes
CoagulaseCoagulase: Coagulate blood KinasesKinases: Digest fibrin clots HyaluronidaseHyaluronidase: Hydrolyses hyaluronic acid CollagenaseCollagenase: Hydrolyzes collagen IgA proteasesIgA proteases: Destroy IgA antibodies SiderophoresSiderophores: Take iron from host iron-
binding proteins Antigenic variationAntigenic variation: Alter surface proteins
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Penetration into the Host Cell
Figure 15.2
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ToxinsToxins
ToxinToxin: Substances that contribute to pathogenicity.
ToxigenicityToxigenicity: Ability to produce a toxin.
ToxemiaToxemia: Presence of toxin in the host's blood.
ToxoidToxoid: Inactivated toxin used in a vaccine.
AntitoxinAntitoxin: 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 largeFigure 15.4b
EndotoxinsEndotoxins
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ExotoxinExotoxin
Source: Mostly Gram +
Relation to microbe: By-products of growing cell
Chemistry: Protein
Fever? No
Neutralized by antitoxin?
Yes
LD50: SmallFigure 15.4a
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ExotoxinsExotoxins
A-B toxins
Figure 15.5
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ExotoxinsExotoxins
Membrane-disrupting toxins Lyse host’s cellsLyse host’s cells by
Making protein channels in the plasma membrane (e.g., leukocidins, hemolysins).
Disrupting phospholipid bilayer.
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ExotoxinsExotoxins
SuperantigensSuperantigens Cause an intense immune response due
to release of cytokines from host cells. Fever, nausea, vomiting, diarrhea,
shock, and death.
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ExotoxinsExotoxins
Specific for a structure or function in host cell
Figure 15.4a
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ExotoxinsExotoxins
ExotoxinLysogenic conversion
Corynebacterium diphtheriae
A-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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EndotoxinsEndotoxins
Figure 15.6
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Cytopathic Effects of Cytopathic Effects of VirusesViruses
Table 15.4
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Pathogenic Properties of Pathogenic Properties of FungiFungi
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 Pathogenic Properties of FungiFungi
Aflatoxin Aspergillus
Mycotoxins Neurotoxins: Phalloidin, amanitin
Amanita
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Pathogenic Properties of Pathogenic Properties of ProtozoaProtozoa
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 Pathogenic Properties of HelminthsHelminths
Use host tissue. Presence of
parasite interferes with host function.
Parasite's metabolic waste can cause symptoms.
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Pathogenic Properties of Pathogenic Properties of AlgaeAlgae
Paralytic shellfish poisoning Dinoflagellates
Domoic acid intoxication Diatoms
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Portals of ExitPortals 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 Mechanisms of PathogenicityPathogenicity
Figure 15.9