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Chapter 15 Microbial Mechanisms of Pathogenicity Biology 205 Chandler-Gilbert Community College Microbial Mechanisms of Pathogenicity Pathogenicity: The ability to cause disease. Virulence: The extent of pathogenicity. Portals of Entry Mucous membranes Skin Parenteral route 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 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 Penetration into the Host Cell Figure 15.2 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. Endotoxins Source: Relation to microbe: Gram – Present in LPS of outer membrane Chemistry: Lipid Fever? Yes Neutralized by antitoxin? No LD50: Relatively large Figure 15.4b Exotoxin Source: Relation to microbe: Chemistry: Mostly Gram + By-products of growing cell Protein Fever? No Neutralized by antitoxin? LD50: Yes 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 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 + Superantigen. + Corynebacterium diphtheriae Staphylococcus aureus 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 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 Mechanisms of Pathogenicity Figure 15.9