Mechanisms of Pathogenicity Notes

Mechanisms of Pathogenicity

• Chapter Overview
  • Topics: Microbiome, Host-Microbe Interactions, Pathogenicity, Opportunistic Infections, Virulence Factors, Toxins, Quorum Sensing, Stages of Infectious Disease.

Microbiota

• Definition
  • Microbiota refers to microorganisms that inhabit our bodies, replacing the outdated term "microflora."
• Types
  • Normal Microbiota: Also known as resident microbiota; permanent residents in specific body areas.
  • Transient Microbiota: Temporary inhabitants; can be present under certain conditions but not permanently.
• Acquisition of Microbiota
  • All sterile before birth, acquiring microbiota from the birthing process and environment afterward.
  • Differences in microbiota based on the method of delivery (vaginal vs. cesarean).

Host-Microbe Interactions

• Contamination: Presence of an organism without causing harm.
• Infection: Microorganism multiplies in host, potentially leading to illness (e.g., staph aureus on a cut).
• Disease: Health disturbance caused by infection; symptoms worsen and disrupt normal bodily functions.
• Infestation: Term reserved for parasitic infections (e.g., tapeworms).

Pathogenicity

• Definition: Capability of an organism to cause infection or disease.
• Factors Affecting Pathogenicity:
  • Ability to invade and multiply in hosts.
  • Quantity of microbes needed for infection (e.g., Shigella can cause illness from one cell).
  • Ability to evade the immune system (e.g., HIV infects immune cells).

Opportunistic Infections

• Definition: Infections caused by normally harmless organisms that become pathogenic under certain conditions.
• Factors for Opportunistic Infections:
  • Immunocompromised individuals: Vulnerabilities due to age, disease, or medications.
  • Unusual locations: Normal microbiota can cause infections if introduced into wrong sites (e.g., E. coli in the urinary tract).
  • Disturbance of Normal Microbiota: Antibiotics can wipe out beneficial microbiota, allowing opportunistic pathogens to flourish (e.g., yeast infections after antibiotics for UTIs).

Types of Infectious Diseases

• Communicable Diseases: Spread easily from person to person.
  • Contagious: Highly communicable (e.g., influenza).
  • Less contagious examples (e.g., pneumonia).
• Non-communicable Diseases: Cannot be spread person to person (e.g., tetanus, malaria).

Virulence Factors

• Definition: Factors that help pathogens cause disease.
• Examples:
  • Pili: Used for attachment to host tissues (e.g., Neisseria gonorrhoeae).
  • Glycocalyx: Enables adherence to surfaces and evasion of the immune system (slime layer vs. capsule).
  • Enzymes:
  • Urease: Neutralizes stomach acid.
  • Hyaluronidase: Breaks down connective tissue, facilitating spread.
  • Collagenase: Destroys collagen, aiding penetration into tissues.

Toxins

• Endotoxins: Found in gram-negative bacteria, released upon death (e.g., E. coli). Associated with low toxicity but serious effects.
• Exotoxins: Secreted by living bacteria, highly toxic (e.g., botulinum toxin).
  • Categories:
  • Neurotoxins: Affect the nervous system (e.g., botulinum toxin).
  • Cytotoxins: Affect cells (e.g., hemolysins, leukocidins).
  • Enterotoxins: Affect intestinal cells (e.g., cholera toxin, staphylococcal enterotoxin).
• Mycotoxins: Fungal toxins causing health issues (e.g., aflatoxins linked to liver cancer).

Quorum Sensing

• Definition: Communication among bacteria using chemical signaling molecules.
• Importance in coordinating group behavior and developing strategies against hosts.
• Concept of anti-quorum sensing molecules as potential broad-spectrum antibiotics.

Stages of Infectious Disease

1. Incubation Period: Time from infection to symptom onset; number of pathogens is low but increasing.
2. Prodromal Phase: Mild signs/symptoms; contagious.
3. Period of Illness: Most acute symptoms; pathogen loads peak.
4. Period of Decline: Symptoms decrease; susceptible to secondary infections.
5. Period of Convalescence: Recovery phase; pathogen levels drop back to normal.

Additional Concepts

• Antigenic Drift: Minor antigenic changes over time due to mutations.
• Antigenic Shift: Major changes resulting from gene mixing between different strains, leading to new viral strains (e.g., influenza).