Bacterial disease-causing mechanisms

Bacterial disease-causing mechanisms

1. Adhesion

   • Attachment of bacteria to host surface
     • Bacterial adhesins
       • Gram +ve or Gram -ve
       • Glycoprotein or lipoprotein
     • Cellular receptors
       • Mannose, sialic acid
     • Glycocalyx
       • Streptococcus mutans
     • Fimbriae
       • E. coli
     • M & Opa proteins
       • Strep. pyogenes; Neiserria gonorrhoea
     • Biofilms

2. Evasion of host defences

   • Capsules
     • Bacterial cell becomes slippery
     • Resistance to phagocytosis
     • Prevents adherence of immune cells
   • Cell wall components
     • M protein (S.pyogenes)
       • Mediates attachment to epithelial cells
       • Inhibits phagocytosis
       • Increases virulence
   • Enzymes
     • Assist in bacterial cell spread throughout host tissue
     • Damage cell membrane - including WBCs

3. Damage Mechanisms

   • Direct
     • Attachment, invasion, multiplication of host cell
     • Production of (harmful) metabolic by-products
   • Toxins
     • Endotoxins
       • Part of cell wall
       • Released upon lysis inside phagocyte
       • Released when killed by antibiotics
       • Activates complement and coagulation cacscade
       • Causes damage to kidneys, lungs, GI tract
     • Exotoxins
       • AB type : Active part --> catalyses cell damage; Binding --> entry into target cell
       • Inhibit cell metabolic functions
       • Cytotoxins --> Diphtheria
       • Neurotoxin --> Tetanus
       • Enterotoxin --> Cholera
   • Induction of hypersensitivity reactions
     • Massive T cell stimulation
     • Excessive cytokine release
     • Staphylococcal Toxic Shock Syndrome Toxin
     • Streptococcal pyrogenic toxin/ erythrogenic toxin