Microbial Mechanisms of Pathogenicity 15 Microbial Mechanisms of Pathogenicity

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

OVERVIEW

OVERVIEW

Portals of Entry or How Microbes Enter a Host Mucous membranes Skin Parenteral route

Portals of Entry or How Microbes Enter a Host

Portals of Entry or How Microbes Enter a Host

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.

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

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

Adherence

How Bacterial Pathogens Penetrate Host Defenses

How Bacterial Pathogens Penetrate Host Defenses Capsule Cell Wall Components – M protein, Opa, mycolic acid

Chemicals that Promote Bacterial Invasions 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 Invasins – cause ruffling of membrane and enhance penetration

Penetration into the Host Cell Figure 15.2

HOST CELL DAMAGE

ROBBING THE HOST CELL OF NUTRIENTS Takes it from: Hemoglobin, lactoferrin, Transferrin, and Ferritin Siderophore with Iron

DIRECT DAMAGE DIRECT DAMAGE OCCURS AS BACTERIAL CELLS MULTIPLY AND RUPTURE INFECTED CELLS.

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.

DISEASES Table 15.4

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

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

Exotoxins A-B toxins Figure 15.5

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

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

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

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 Vibrio cholerae A-B toxin. Enterotoxin Staphylococcus aureus Superantigen.

Endotoxins Figure 15.6

Cytopathic Effects of Viruses Table 15.4

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

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

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

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

Pathogenic Properties of Algae Paralytic shellfish poisoning Dinoflagellates Domoic acid intoxication Diatoms Figure 27.15

Figure 15.9 (5 of 5)

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