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Bacterial pathogenesis


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  • 1. ‫بسم ا الرحمن الرحيم‬ BACTERIAL PATHOGENESIS Prof. Khalifa Sifaw Ghenghesh Dept. of Medical Microbiology, Faculty of Medicine, Tripoli University, Tripoli-Libya
  • 2. The Pathogen: • A Disease Producing Microorganism. Pathogenicity: • Capacity to Initiate Disease. Virulence: • Capacity to Harm the Host. • Refer to Degree of Pathogenicity. Opportunistic Pathogens: • Common or Non Pathogenic Microbes. e.g. Normal Flora of the Body.
  • 3. Infection: • The Lodgement and Multiplication of a Parasite in or on the Tissues of a Host. Disease: • A Rare Consequence of Infection. Measurement of Virulence: • The Median Lethal Dose (LD50) is Used. • Number of Microorganisms or Micrograms of Toxin Required to Kill 50% of Infected Animals.
  • 4. Koch's Postulates Isolated • diseased not healthy people Growth • pure culture Induce disease • susceptible animals Re-isolated • susceptible animals
  • 5. PATHOGENICITY Virulence factors (Determinants of pathogenicity) Number of initial organisms Immune status
  • 7. Virulence factors help bacteria to: • Invade the host, • Cause disease, and • Evade host defenses.
  • 8. Toxigenicity. 1 Tissue injury: • Exotoxins: • Include several types of protein toxins and enzymes produced and/or secreted from pathogenic bacteria. • Include cytotoxins, neurotoxins, and enterotoxins.
  • 9. • Endotoxins: • Lipopolysaccharide • Gram-negative bacteria • Endotoxic (Septic) Shock: • Hypotension (tissue pooling of fluids) • Disseminated intravascular coagulation • Fever • Lack of effective oxygenation • Overall system failure
  • 10. Differentiation of Exotoxins and Endotoxins. Exotoxins Endotoxins --------------------------------------------------------------------------------------- -Excreted by living cells. -Relatively unstable. -Highly antigenic; stimulate the formation of high-titer antitoxin. -Converted into antigenic, nontoxic toxoids. -Highly toxic. -Do not produce fever in host. -Released after death of bacteria. -Relatively stable. -Do not stimulate formation of antitoxin. -Not converted into toxoids. -Weakly toxic. -Often produce fever in host.
  • 11. Invasiveness. 2 Capacity of a pathogen to spread in the host tissues after establishing infection. Surface components that allow the bacterium to invade host cells can be encoded on plasmids, but more often are on the chromosome.
  • 12. Penetration and spread Epithelium Salmonella typhi Salmonella enteritidis Vibrio cholerae
  • 13. 3. Capsules Antiphagocytic structures Polysacchride
  • 14. Adhesion. 4 The Relatively Stable, Irreversible Attachment of Bacteria to a Surface. • Fimbrial Adhesins • Nonfimbrial Proteinaceous Adhesins.
  • 15. BACTERIUM adhesin receptor EPITHELIUM
  • 16. E. coli with fimbriae (Pili)
  • 17. 5. Siderophores Iron-binding factors that allow some bacteria to compete with the host for iron, which is bound to hemoglobin, transferrin, and lactoferrin.
  • 18. 6. Other Aggressions Mainly Enzymes: • • • • • Hyaluronidase >> Spreading Factor. Coagualse >> Thrombin - Like Enzyme. Fibrinolysin >> Streptokinase. Proteases >> Hydrolyse Immunoglobulins. Others