Foundation in Microbiology 5ed

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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
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
Exotoxin
Lysogenic
conversion
Corynebacterium diphtheriae
A-B toxin.
Inhibits protein synthesis.
+
Streptococcus pyogenes
Membrane-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