Bacterial Pathogenicity: Features Increasing Pathogenicity

Bacterial Features Increasing Pathogenicity

The Balance Between Health and Disease

  • The state of being well versus being unwell is a balance between disease and health.
  • A young and healthy person's host resistance typically outweighs microbe virulence.
    • Host: An organism harboring a microbe (typically humans).
  • When microbe virulence exceeds host resistance, disease occurs.

Adherence: Sticking to the Host

  • Adherence enables bacteria to stick to the host.
  • Capsules, slime layers, and fimbriae facilitate adherence.
  • Adherence is crucial for bacteria invading via mucous membranes.
    • The body attempts to remove bacteria through sneezing or coughing.
    • Firmly attached bacteria avoid expulsion and persist.
Mechanisms of Adherence
  • Staphylococcus pyogenes attaches to proteins on human epithelial cells.
  • Adhesins: Molecules on bacteria that bind to specific chemicals on host cells.
    • Adhesins have specific structural shapes for attachment.
    • Found on fimbriae or pili.
  • Pili: Hair-like structures with adhesive tips that match proteins on cell surfaces.
Examples of Adherence
  • Escherichia coli (E. coli) strains with pili attach to the bladder and kidney, causing urinary tract infections (UTIs).
  • E. coli strains lacking pili are flushed out and do not cause UTIs.
  • Only specific strains of E. coli cause UTIs due to their ability to stick.

Slime Layers and Biofilms

  • Bacteria secrete a sticky substance made of polysaccharide polymers and glycocalyx.
Biofilm Formation
  • Bacteria stick together to form a layer, then layer upon layer, creating a biofilm.
  • Biofilms cement bacteria together into a sticky layer on surfaces or tissues.
Examples and Implications
  • Streptococcus mutans: Responsible for tooth decay.
    • Uses a glycocalyx of polysaccharide to attach to the tooth surface, colonizing and producing acid.
    • Forms plaque and causes tooth decay.
Biofilms on Medical Devices
  • Biofilms form on heart valves, endotracheal tubes, urinary catheters, and central venous catheters.
  • Once formed, biofilms are almost impossible to remove.
Protection Mechanisms
  • The glycocalyx forms a physical barrier that human defense cells cannot penetrate.
  • Biofilms protect against antibiotics.
    • The polysaccharide layer prevents antibiotic diffusion.
  • Biofilms pose a significant problem in healthcare.