Chapter 15Chapter 15Microbial Microbial

MechanismsMechanismsof Pathogenicityof Pathogenicity

Biology 205Biology 205

Chandler-Gilbert Community CollegeChandler-Gilbert Community College

Microbial Mechanisms of Microbial Mechanisms of PathogenicityPathogenicity

PathogenicityPathogenicity: The ability to cause disease.

VirulenceVirulence: The extent of pathogenicity.

Portals of EntryPortals of Entry

Mucous membranesMucous membranes SkinSkin Parenteral routeParenteral route

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.

Portal of Entry ID50

Skin 10-50 endospores

Inhalation 10,000-20,000 endospores

Ingestion 250,000-1,000,000 endospores

Bacillus AnthracisBacillus Anthracis

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

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

Penetration into the Host Cell

Figure 15.2

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.

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

ExotoxinExotoxin

Source: Mostly Gram +

Relation to microbe: By-products of growing cell

Chemistry: Protein

Fever? No

Neutralized by antitoxin?

Yes

LD50: SmallFigure 15.4a

ExotoxinsExotoxins

A-B toxins

Figure 15.5

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.

ExotoxinsExotoxins

SuperantigensSuperantigens Cause an intense immune response due

to release of cytokines from host cells. Fever, nausea, vomiting, diarrhea,

shock, and death.

ExotoxinsExotoxins

Specific for a structure or function in host cell

Figure 15.4a

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. +

EndotoxinsEndotoxins

Figure 15.6

Cytopathic Effects of Cytopathic Effects of VirusesViruses

Table 15.4

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

Pathogenic Properties of Pathogenic Properties of FungiFungi

Aflatoxin Aspergillus

Mycotoxins Neurotoxins: Phalloidin, amanitin

Amanita

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

Pathogenic Properties of Pathogenic Properties of HelminthsHelminths

Use host tissue. Presence of

parasite interferes with host function.

Parasite's metabolic waste can cause symptoms.

Pathogenic Properties of Pathogenic Properties of AlgaeAlgae

Paralytic shellfish poisoning Dinoflagellates

Domoic acid intoxication Diatoms

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

Mechanisms of Mechanisms of PathogenicityPathogenicity

Figure 15.9