Chapter 12: Microbial Pathogenicity PathogenicityThe ability to cause disease VirulenceThe extent of pathogenicity

Mucous membranes Skin Parenteral route Portals of Entry

ID 50 : Infectious dose for 50% of the test population LD 50 : Lethal dose (of a toxin) for 50% of the test population Numbers of Invading Microbes

Bacillus anthracis Portal of entryID 50 Skin10-50 endospores Inhalation10,000-20,000 endospores Ingestion250,000-1,000,000 endospores

Adhesins/ligands bind to receptors on host cells GlycocalyxStreptococcus mutans FimbriaeEscherichia coli Streptococcus pyogenes Neisseria gonorrhoeae Adherence of Microbe

Coagulates blood Digests fibrin clots HyaluronidaseHydrolyzes hyaluronic acid CollagenaseHydrolyzes collagen Pathogenicity Promoters

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pathogenicity Promoters IgA proteasesDestroy IgA antibodies SiderophoresTake iron from host iron- binding proteins Alter surface proteins

Penetration into the Host Cell Figure 15.2

Toxins ToxinSubstances that contribute to pathogenicity ToxigenicityAbility to produce a toxin ToxemiaPresence of toxin in the host's blood ToxoidInactivated toxin used as a vaccine i.e. diptheria and tetanus toxoid AntitoxinAntibodies against a specific toxin

Endotoxin Figure 15.4b

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Endotoxin

Endotoxins Figure 15.6

Endotoxins SourceGram negative bacteria LocationOuter membrane ChemistryLipopolysaccharide (LPS) → Lipid A Fever?Yes Neutralized by antitoxinNo LD 50 Relatively large

Exotoxins Figure 15.4a

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

Membrane-disrupting toxins Lyse host cells by: Making protein channels in the plasma membrane (e.g., ) Disrupting phospholipid bilayer S. aureus and Streptococci Types of Exotoxins

A-B toxins Disrupts internal cellular mechanisms; Clostridium botulinum produces an A-B neurotoxin Vibrio cholerae produces an A-B enterotoxin Types of Exotoxins Figure 15.5

Exotoxins Exotoxin Lysogenic conversion Clostridium botulinumA-B toxin - Neurotoxin+ Vibrio choleraeA-B toxin - Enterotoxin+

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Exotoxin SourceMostly Gram positive locationSecreted by cell ChemistryProtein Fever?Type I (Superantigens) Neutralized by antitoxinYes LD 50 Small

Fungal metabolic waste products may cause allergies Proteases Vaginal yeast infection Capsule prevents phagocytosis LINK Can cause skin or nervous tissue disease Found in soil and pigeon droppings Pathogenic Properties of Fungi

Aflatoxin; second link Aflatoxinsecond link Aspergillus flavus Infrequently, contaminated peanut butter recalled Neurotoxins mushrooms May be fatal if ingested Ergot toxin Claviceps purpurea Pathogenic Properties of Fungi

Avoid host defenses by Growing inside host cell i.e. Antigenic variation Avoiding host immune system campers: be careful what you drink! Pathogenic Properties of Protozoa

Presence of parasite may interfere with host function i.e. parasite clogs lymphatic vessels linklink Pathogenic Properties of Helminths Pathogenic Properties of Algae Neurotoxins produced by - Paralytic shellfish poisoning

Respiratory tract Coughing, sneezing Gastrointestinal tract Feces, saliva Genitourinary tract Urine, vaginal secretions, semen Skin Skin infections Blood Biting arthropods, needles/syringes Portals of Exit

Mechanisms of Pathogenicity