Microbial Mechanisms of Pathogenicity - Study Notes

Microbial Mechanisms of Pathogenicity

Key Terms

  • Pathogenicity: Ability to cause disease.

  • Virulence: Degree of pathogenicity.

Portals of Entry

  • Mucous Membranes: Includes respiratory, digestive, reproductive, urinary tracts, and eyes.

  • Skin: Both broken and unbroken skin, including pores and follicles.

  • Parenteral Route: Entry via punctures, bites, cuts, wounds, or surgical procedures.

Common Pathogens and Their Portals of Entry

Table 15.1: Lists various pathogens, their entry portals, associated diseases, and incubation periods. Examples include:

  • Respiratory Tract:

    • Streptococcus pneumoniae - Pneumococcal pneumonia (Variable incubation)

    • Influenza virus - Influenza (18-36 hours)

    • Mycobacterium tuberculosis - Tuberculosis (Variable)

  • Gastrointestinal Tract:

    • Vibrio cholerae - Cholera (1-3 days)

    • Salmonella spp. - Salmonellosis (6-14 days)

    • Hepatitis A virus - Hepatitis A (2-28 days)

  • Genitourinary Tract:

    • Neisseria gonorrhoeae - Gonorrhea (3-8 days)

    • Human Immunodeficiency Virus (HIV) - AIDS (10 years latent)

  • Skin/Parenteral Route:

    • Clostridium tetani - Tetanus (3-21 days)

    • Rabies virus - Rabies (10 days-1 year)

Dose Testing

  • ID50: Infectious dose for 50% of the test population.

  • LD50: Lethal dose for 50% of test population.

  • Example: Bacillus anthracis

    • ID50 via skin: 10-50 endospores

    • ID50 via inhalation: 10,000-20,000 endospores

    • ID50 via ingestion: 250,000-1,000,000 endospores

Virulence Factors

  • A. Glycocalyx: Protection via sugar coating, can form biofilms:

    • Capsule (Organized, e.g., Streptococcus pneumoniae)

    • Slime Layer (Less organized, e.g., Pseudomonas aeruginosa)

  • B. Enzymes: Contribute to virulence by damaging host tissues:

    • Coagulases: Form clots to protect pathogens.

    • Kinases: Breakdown clots to allow spread.

    • Hemolysins: Damage red blood cells.

    • M-protein: Helps Streptococcus pyogenes resist phagocytosis.

  • C. Pili: Hair-like structures that aid adherence through specific binding to host cell receptors.

  • D. Toxins:

    • Exotoxins: Protein toxins secreted by bacteria; highly toxic and specific effects (e.g., Clostridium botulinum).

    • Endotoxins: Part of Gram-negative cell wall (Lipid A) that produces general systemic effects like fever.

Cytopathic Effects (CPE)

  • CPE: Structural or functional changes in host cells due to viral infection (e.g., cell lysis, inclusion bodies, cell fusion).

Mechanisms of Pathogenicity Overview

  1. Portals of Entry: Multiple routes including mucous membranes, skin, and parenteral route.

  2. Adherence and Evasion: Involves adherence mechanisms and evasion of host defenses.

  3. Damage to Host Cells: Via toxins, enzymes, and direct cell damage.

  4. Portals of Exit: Generally the same as portals of entry.

Virulence and Disease Process

  • Pathogens employ various mechanisms such as antigenic variation, intracellular growth, and immune evasion to establish infections and cause diseases.

  • Siderophores: Compete with host's iron to support bacterial growth.

This concludes the detailed overview of Chapter 15 on microbial mechanisms of pathogenicity. Please refer to specific tables and diagrams in the textbook for visual representations and further details on pathogens and their mechanisms.