MICROBIOLOGY ROBERT W. BAUMAN Chapter 14 Pathogenicity
Microbial Mechanisms of Pathogenicity Pathogenicity -The ability to cause disease Virulence - The extent of pathogenicity Virulence Factors Adhesion factors Extracellular enzymes Toxins Antiphagocytic factors
Numbers of Invading Microbes ID 50 : Infectious dose for 50% of the test population LD 50 : Lethal dose (of a toxin) for 50% of the test population
Bacillus anthracis Portal of entry ID 50 Skin Inhalation 10-50 endospores 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
Adhesins Proteins Surface lipoproteins or glycoproteins, called ligands, bind host cell receptors Ability to change or block the ligand or its receptor can prevent infection Inability to make attachment proteins or adhesins renders the microorganisms avirulent
Exoenzymes 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
Toxin Toxins Substances that contribute to pathogenicity Toxigenicity Ability to produce a toxin Toxemia Toxoid Antitoxin Presence of toxin the host's blood Inactivated toxin used in a vaccine Antibodies against a specific toxin
Exotoxin Source *Mostly Gram + Metabolic product By-products of growing cell Chemistry Protein Fever? No Neutralized by antitoxin LD 50 Yes Small
Exotoxins Figure 15.4a
Exotoxins A-B toxins or type III toxins Figure 15.5
Exotoxins Superantigens or type I toxins Cause an intense immune response due to release of cytokines from host cells Fever, nausea, vomiting, diarrhea, shock, death
Exotoxins Membrane-disrupting toxins or type II toxins Lyse host s cells by: Making protein channels in the plasma membrane (e.g., leukocidins, hemolysins) Disrupting phospholipid bilayer
Exotoxins Corynebacterium diphtheriae Streptococcus pyogenes Exotoxin A-B toxin. Inhibits protein synthesis. Membrane-disrupting. Erythrogenic. Lysogenic conversion + + Clostridium botulinum A-B toxin. Neurotoxin + C. tetani A-B toxin. Neurotoxin Vibrio cholerae A-B toxin. Enterotoxin + Staphylococcus aureus Superantigen. Enterotoxin.
Endotoxin Figure 15.4b
Endotoxins Source Metabolic product Chemistry Fever? Neutralized by antitoxin LD 50 Gram Present in LPS of outer membrane Lipid Yes No Relatively large
Endotoxins Figure 15.6
Antiphagocytic Factors Certain factors prevent phagocytosis by the host s phagocytic cells Bacterial capsule Can be slippery making it difficult for phagocytes to engulf the bacteria Often composed of chemicals found in the body and not recognized as foreign Antiphagocytic chemicals Some prevent fusion of lysosome and phagocytic vesicles Leukocidins directly destroy phagocytic white blood cells
Cytopathic Effects of Viruses Table 15.4
Pathogenic Properties of Fungi Fungal waste products may cause symptoms Chronic infections provoke an allergic response Mycotoxins Neurotoxins: Phalloidin, α-amanitin Amanita Aflatoxin Aspergillus
Pathogenic Properties of Fungi Ergot toxin: alkaloid Claviceps Tichothecene toxins inhibit protein synthesis Fusarium Proteases Candida, Trichophyton Capsule prevents phagocytosis Cryptococcus
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 Neurotoxins produced by dinoflagellates Saxitoxin Paralytic shellfish poisoning
Mechanisms of Pathogenicity Figure 15.9