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Microbial Systems of Pathogenicity

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  1. Microbial Mechanisms of Pathogenicity Dr. Ackman

  2. Definitions • Pathogenicity • Ability of a microorganism to cause disease by overcoming the defenses of a host • Virulence • The degree or extent of pathogenicity

  3. Portals of Entry • Pathogens • Must gain access to host • Adhere to host tissue • Penetrate or evade host defenses • Damage host tissue

  4. Portals of Entry • Portal of Entry • Routes microorganisms can penetrate the body • 1- mucous membranes • 2- skin • 3- parenteral route

  5. Mucous membrane entry • Mucous membranes • Respiratory tract • Easiest and most frequent route of infection • Inhaled through nose or oral cavity • Duct particles, moisture droplets • Common cold, pneumonia, tuberculosis, influenza and smallpox

  6. Mucous Membrane Entry • Mucous membrane • Gastrointestinal route • In food or water • Contaminated fingers • Most are inactivated by stomach acid, enzymes, bile • Poliomyelitis, hepatitis A, amoeboid dysentery, cholera

  7. Mucous Membrane Entry • Mucous membrane • Genitourinary tract • Contracted sexually • Intact or broken mucus membranes • STI (sexually transmitted infections) • HIV, genital warts, genital herpes, syphilis, and gonorrhea

  8. Skin • Skin • Unbroken skin – barrier to microorganisms • Hair follicles and sweat gland ducts • Some pathogens penetrate normal skin • Hookworm larva • Some pathogens grow on keratin of skin • Ringworm • Abscesses, burns

  9. Parenteral Route • Parenteral route • Microorganisms deposited directly below skin • Puncture wounds, injections, bites, wounds, and surgery • Tetanus, rabies, Hepatitis B, and malaria

  10. Preferred Portal of entry • Some organisms must enter via preferred route to cause disease • Some organisms may cause disease with many different route of entry

  11. Preferred Portal of Entry

  12. Numbers of Invading Organisms • Disease more likely with more organisms (pathogens) • ID50- infectious dose for 50% of a sample population • Measures virulence of a microorganism • Anthrax • Cutaneous (skin) ID50 10-50 endospores • Inhalation ID50 10,000-20,000 endospores • Gastrointestinal ID50 250,000 – 1,000,000 endospores

  13. Numbers of Invading Microbes • LD50 – lethal dose for 50% of a sample population • Measures potency of toxins • LD50 • Botulinum toxin = 0.03 ng/kg • Shiga toxin = 250 ng/kg • Staphylococcal enterotoxin = 1350 ng/kg

  14. Adherence of microorganisms • Microorganisms after entry into host must adhere to host • Adherence • Attachment of microorganisms after entry to host • Surface molecules • Ligands and adhesins bind specifically for receptors on host cells. • Glycocalyx, pili, fimbrae, flagella

  15. Adherence

  16. Adherence • Receptors of host cells • Usually a sugar • i.e. mannose • Altering receptor, adhesin, or both alters ability for infection to occur

  17. Adherence • An example • Streptococcus mutans attaches to teeth by its glycocalyx • Actinomyces have fimbrae that adhere to glycocalyx of S. mutans • Involved in dental caries (cavities) • E. coli have adhesins on fimbrae, attach to specific regions of small intestine

  18. Biofilms • Biofilms • Communities of microorganisms and their extracellular products that attach to non-living and living surfaces • Algae • Dental plaque • Medical catheters

  19. How pathogens penetrate host defenses • Capsules • Impair phagocytosis • Prevents phagocytic cell from attaching to microorganism • Made of glycocalyx • Streptococcus pneumoniae • Griffith’s experiment of genetic transformation

  20. How pathogens penetrate host defenses • Components of Cell Wall • M – protein • Mediates attachment to epithelium • Resists phagocytosis • Opa • Outer membrane protein • Helps in attachment • Waxes • Resist digestion by phagocytes • Mycobacterium

  21. How pathogens penetrate host defenses • Enzymes • Extracellular enzymes (exoenzymes) • Dissolve material between cells, form or dissolve clots • Coagulase • Converts fibrinogen to fibrin clot • Isolates microorganism from host defenses • Kinases • Break down fibrin • Hyaluronidase • Breaks down cell to cell adhesions in connective tissue • Collagenase • Produced by several Clostridium sp • Breaks down protein collagen • IgA proteases • Destroy antibodies

  22. How pathogens penetrate host defenses • Antigenic variation • Pathogens alter surface proteins • Several versions of Opa protein • New antibodies must be produced • Gonorrhea • Sleeping sickness • Influenza

  23. How pathogens penetrate host defenses • Penetration into host cells cytoskeleton • Invasins • Rearrange actin filaments • Facilitates movement of microorganism into cell

  24. How Pathogens Damage Host Cells • 1- utilize host’s nutrients • 2- direct damage in immediate vicinity of infection • 3- toxin production

  25. How pathogens penetrate host defenses • Using host’s nutrients • Siderophores • Bind iron away from host’s iron binding proteins • Direct Damage • Multiplication of microorganism within cell • Viruses • Bacterial • Protozoal

  26. Toxins • Toxin • Poisonous compound produced by microorganisms • Often the pathogenic component of a microorganism • Toxigenicity • Ability of a microorganism to produce a toxin • Toxemia • Presence of toxin within the blood

  27. Toxins • Toxins • Fever • Cardiovascular abnormalities • Diarrhea • Shock • Destroy blood cells • Destroy blood vessels • Disrupt nervous system

  28. Exotoxins • Exotoxins • Produced inside the bacteria as part of growth • Secreted by the bacteria into surrounding environment • Exotoxins are proteins • Enzymes that catalyze chemical reactions • Can be used over and over • Gram – or gram + bacteria • Genes carried on plasmid • Inhibit certain metabolic functions • Very toxic • Botulinum toxin 1 mg kill 1,000,000 people

  29. Exotoxins • Exotoxins • Readily diffuse into body fluids and tissue • Disease specific • Disease caused by the exotoxin, not the infection itself • Antitoxins • Body production of antibodies against the toxin • Toxoids • Toxin inactivated by heat or other chemicals (formaldehyde) • Still initiate production of antibodies • Injected into the body (toxoid vaccination) • Tetanus • Diphtheria

  30. Exotoxins • 3 types of exotoxins • 1- A-B Toxins • Also called type III toxins • Most exotoxins fall into this category • A component • Active enzyme component • B component • Binding component

  31. Exotoxins • A-B toxins • A-B toxin released by bacteria • B part binds to receptor of host cell • Toxin transported across membrane into cell • A-B components separate • A component inhibits protein synthesis and kills cell

  32. Exotoxins • Exotoxins • 2 – Membrane disrupting toxin • Type II toxins • Causes lysis of cells by disrupting cell membrane • Form protein channels • Staphylococcus aureus • Disrupt phospholipids • Clostridium perfringens • Leukocidins • Membrane disrupting toxins that kill phagocytic WBC’s • Hemolysins • Membrane disrupting toxins that kill erythrocyes RBC’s

  33. Exotoxins • Exotoxins • 3- Superantigens • Type I toxins • Provoke intense immune response • Protein in nature (antigens) • Stimulate T – cells • Release cytokines (too much) • Causes fever, nausea, vomiting diarrhea

  34. Exotoxins • Neurotoxins • Attack nerve cells • Cardiotoxins • Attack cardiac cells • Hepatotoxins • Attack liver cells • Enterotoxins • Attack lining of GI tract • Cytotoxin • Attacks wide variety of cells

  35. Specific Exotoxins • Diphtheria toxin • Cornybacterium diphtheriae • Requires lysogenic phage carrying tox gene • Cytotoxin inhibits protein synthesis in eukaryotic cells • Erythrogenic toxins • Streptococcus pyogenes • A,B,C toxins damage plasma membranes of capillaries under skin causing rash • Scarlet fever

  36. Specific Exotoxins • Botulinum toxin • Clostridium botulinum • Acts on neuromuscular junction • Prevents nerve impulse transmission • Inhibits release of neurotransmitter acetylcholine • Causes flaccid paralysis • Tetanus toxin • Clostridium tetani • Tetanospasmin • CNS blocks inhibitory neurons to skeletal muscle • Results in uncontrollable muscle contractions • Lock jaw

  37. Specific Exotoxins • Vibrio enterotoxin • Vibrio cholerae • Produces cholera toxin • Sub unit B attaches to epithelium of intestinal tract • Sub unit A causes cells to secrete large amounts of electrolytes causing diarrhea

  38. Specific Exotoxins • Staphylococcal enterotoxin • Staphylococcus aureus • Similar to cholera toxin

  39. Exotoxins

  40. Endotoxins • Endotoxins • Part of the outer membrane • Lipopolysaccharides (LPS) • Lipid A • Released when g- bacteria undergo lysis and multiplication • Antibiotics?

  41. Endotoxins • Endotoxins • Cause WBC to release cytokines • Toxic at these levels • Cause chills, fever, weakness, generalized aches, shock and death • Can cause activation of blood clotting mechanisms causing tiny blood clots • Disseminated intravascular clotting (DIC)

  42. Endotoxins

  43. Endotoxins vs. Exotoxins

  44. Plasmids • Plasmid genes may make bacteria resistant to some antibiotics • Plasmids may carry other virulence factors such as toxin production, fimbrae

  45. Lysogeny • Lysogeny • Bacteriophages incorporate DNA into bacterial chromosomes • Viruses remain latent within bacterium, not causing lysis • May create bacteria with new genome • Called lysogenic conversion • Some bacteria require infection by bacteriophage to be pathogenic • Diphtheria toxin

  46. Pathogenic Properties of Viruses • Cytopathic effects of viruses • Animal viruses usually cause death of host cell • Accumulation of multiplying viruses • Alter permeability of cell membrane • Inhibit host DNA or RNA • Cytopahtic effects (CPE) • Visible effects of viral infection • cytocidal or noncytocidal

  47. CPE’s • 1. Macromolecule synthesis halted • Mitosis inhibited (Herpes virus) • 2. Release of lysosomes within cell an destruction of cellular contents • 3. Inclusion bodies • Viral parts, nucleic acids • Various size and staining characteristics • Eosinophilic, basophilic • Negri bodies (Rabies)

  48. CPE’s • 4. Syncytium • Adjacent infected cells fuse • 5. Changes in host cell functions • 6. Cause the host cell to produce interferons • 7. Antigenic changes on plasma membrane • 8. Chromosomal changes in host cell and conversion of oncogenes • 9. Transformation of host cell • Cause spindle shaped cells • Lack contact inhibition

  49. Fungal pathogenic properties • Secretion of enzymes • Proteases • Capsules • Toxins • Ergot • Aflatoxin

  50. Protozoal Pathogenic Properties • Protozoal • Rupture of cells • Malaria • Digest cells and tissue • Alter surface antigens • 1,000 different antigens