Overview
This lecture explains how bacteria adapt to and damage the human body, focusing on their methods of entry, colonization, toxin production, immune evasion, and the resulting disease symptoms.
Bacterial Adaptation & Host Interaction
- Bacteria adapt over time by gaining or losing genetic traits for survival in specific environments.
- Virulence factors are traits that enable bacteria to cause disease by damaging the host.
- Disease severity depends on affected tissue, bacterial strain, inoculum size, and host immune status.
Mechanisms of Entry & Colonization
- The human body’s defenses include skin, earwax, stomach acid, tears, and mucous membranes.
- Bacteria can enter via ingestion (Salmonella, Shigella), inhalation (Streptococcus, Legionella), wounds (Clostridium tetani), insect bites, needlestick injuries, or sexual transmission.
- Bacteria use fimbriae, pili, and adhesins to attach to host surfaces.
- Biofilms, sticky bacterial communities, protect bacteria from antibiotics and immunity (e.g., on catheters, dental plaque).
Bacterial Damage & Toxin Production
- Some bacteria destroy tissue via byproducts like enzymes, gas, and acids (e.g., Staphylococci, Streptococci).
- Toxins can damage host cells locally or throughout the body when distributed by blood.
- Cell wall components, like peptidoglycan (gram-positive) and lipopolysaccharide/endotoxin (gram-negative), trigger strong immune responses.
- Exotoxins, which are proteins, can cause cell lysis, cell death, or alter cell function.
- Superantigens are toxins that excessively activate the immune system, leading to toxic shock syndrome.
Immune Evasion Strategies
- Bacteria may alter surface proteins, hide within host cells, or inactivate antibacterial defenses.
- Capsules mimic host cells, helping bacteria avoid immune detection.
- Some bacteria (e.g., Staphylococcus aureus) create physical barriers at infection sites.
Key Terms & Definitions
- Virulence factor — A trait that increases a bacterium's ability to cause disease.
- Inoculum size — Number of bacterial cells required to establish an infection.
- Biofilm — A community of microorganisms encased in a protective matrix.
- Exotoxin — A toxic protein secreted by bacteria, causing damage to host cells.
- Endotoxin (lipopolysaccharide) — A component of gram-negative bacterial cell walls that triggers immune responses.
- Superantigen — A toxin causing excessive immune activation and toxic shock.
- Capsule — A slime layer surrounding some bacteria, aiding in immune evasion.
Action Items / Next Steps
- Review bacterial entry, colonization, and immune evasion mechanisms.
- Prepare for the next lecture on specific bacterial infection examples in humans.