Copyright © 2010 Pearson Education, Inc. MICROBIAL MECHANISMS OF PATHOGENICITY Chapter 15

Copyright © 2010 Pearson Education, Inc. Mechanisms of Pathogenicity  Pathogenicity: The ability to cause disease  Virulence: The extent of pathogenicity, the amount of “damage” done

Copyright © 2010 Pearson Education, Inc. Portals of Entry  Mucous membranes- nose/ mouth/ lungs/ intestines  Skin  Parenteral route- injection/ IV/ wound  Preferred portal of entry

Copyright © 2010 Pearson Education, Inc. Portals of Entry  Streptococcus pneumoniae  if inhaled can cause pneumonia  if enters the G.I. Tract, no disease  Salmonella typhi  if enters the G.I. Tract can cause Typhoid Fever  if on skin, no disease

Copyright © 2010 Pearson Education, Inc. Portal of EntryID 50 Skin10–50 endospores Inhalation10,000–20,000 endospores Ingestion250,000–1,000,000 endospores Bacillus anthracis

Copyright © 2010 Pearson Education, Inc. Portal of EntryID 50 Botulinum0.03 ng/kg Shiga toxin250 ng/kg Staphylococcal enterotoxin1350 ng/kg Toxins Shiga:1/160 th of human hair

Copyright © 2010 Pearson Education, Inc. Adherence  Adhesins/ligands bind to receptors on host cells  Glycocalyx: Streptococcus mutans  Fimbriae: Escherichia coli  M protein: Streptococcus pyogenes  Form biofilms

Copyright © 2010 Pearson Education, Inc. Adherence Figure 15.1

Copyright © 2010 Pearson Education, Inc. Adherence Figure 15.1

Copyright © 2010 Pearson Education, Inc. Adherence Figure 15.1

Copyright © 2010 Pearson Education, Inc. Capsules  Prevent phagocytosis  Streptococcus pneumoniae  Haemophilus influenzae  Bacillus anthracis

Copyright © 2010 Pearson Education, Inc. Cell Wall Components  M protein resists phagocytosis  Streptococcus pyogenes  Opa protein inhibits T helper cells  Neisseria gonorrhoeae  Mycolic acid (waxy lipid) resists digestion  Mycobacterium tuberculosis

Copyright © 2010 Pearson Education, Inc. Enzymes  Coagulase: Coagulates fibrinogen  Kinases: Digest fibrin clots  Hyaluronidase: Hydrolyzes hyaluronic acid  Collagenase: Hydrolyzes collagen  IgA proteases: Destroy IgA antibodies

Copyright © 2010 Pearson Education, Inc. Membrane Ruffling Figure 15.2

Copyright © 2010 Pearson Education, Inc. Antigenic Variation  Alter surface proteins Figure 22.16

Copyright © 2010 Pearson Education, Inc.  Invasins  Salmonella alters host actin to enter a host cell  Use actin to move from one cell to the next  Listeria Penetration into the Host Cell Cytoskeleton Figure 15.2 Salmonella

Copyright © 2010 Pearson Education, Inc. Direct Damage  Disrupt host cell function  Produce waste products  Toxins

Copyright © 2010 Pearson Education, Inc. The Production of Toxins  Toxin: Substance that contributes 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

Copyright © 2010 Pearson Education, Inc. Figure 15.4 Exotoxins and Endotoxins

Copyright © 2010 Pearson Education, Inc. Exotoxins  Specific for a structure or function in host cell Figure 15.4a

Copyright © 2010 Pearson Education, Inc. Membrane-Disrupting Toxins  Lyse host’s cells by  Making protein channels in the plasma membrane –Leukocidins –Hemolysins –Streptolysins  Disrupting phospholipid bilayer

Copyright © 2010 Pearson Education, Inc. Superantigens  Cause an intense immune response due to release of cytokines from host cells  Symptoms: fever, nausea, vomiting, diarrhea, shock, and death

Copyright © 2010 Pearson Education, Inc. Endotoxins and the Pyrogenic Response Figure 15.6

Copyright © 2010 Pearson Education, Inc. LAL Assay  Limulus amoebocyte lysate assay  Amoebocyte lysis produces a clot  Endotoxin causes lysis

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. Pathogenic Properties of Fungi  Ergot toxin  Claviceps  Aflatoxin  Aspergillus  Mycotoxins  Neurotoxins: Phalloidin, amanitin  Amanita

Copyright © 2010 Pearson Education, Inc. Pathogenic Properties of Protozoa  Presence of protozoa  Protozoan waste products may cause symptoms  Avoid host defenses by  Growing in phagocytes  Antigenic variation

Copyright © 2010 Pearson Education, Inc. Pathogenic Properties of Helminths  Use host tissue  Presence of parasite interferes with host function  Parasite's metabolic waste can cause symptoms

Copyright © 2010 Pearson Education, Inc. Pathogenic Properties of Algae  Paralytic shellfish poisoning  Dinoflagellates  Saxitoxin Figure 27.13

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. Mechanisms of Pathogenicity Figure 15.9