6.2-6.4 ( bacteria as pathogens + antibiotics)

• pathogen


  micro organism which causes disease.
• how do bacteria harm host cells?

  • invade and destroy host tissue
  • produce toxins
• what are the types of toxins?

  • endotoxin
  • exotoxin
• Endotoxin

  • lipopolysaccharides
  • on cell membrane of gram negative bacteria
  • released when bacterial cells die
  • cause local inflammation
• exotoxin

  • secreted by living bacteria
  • release toxins in host cell
  • systemic affect
• examples of endotoxins

  • salmonella spp
  • triggers release of cytokines
  • releases endotoxins into host cell when bacteria dies
• examples of exotoxins

  • staphylococcus spp
  • releases exotoxins which are proteins.
• types of antibiotics

  • bactericidal
  • bacteriostatic
• bactericidal antibiotics

  • kills bacteria
• bacteriostatic antibiotics

  • prevent bacteria multiplying
  • doesn't kill bacteria
• examples of bacteriostatic antibiotic. how does it work?

  • tetracycline
  • prevents ribosomes forming in Gram + and - bacteria
  • prevents protein synthesis
  • so tRNA cant attach
  • inhibits growth and division
• examples of bactericidal antibiotics. how do they work?

  • penicillin
  • prevents formation of peptidoglycan
  • in gram negative bacteria
• causes for antibiotic resistance

  • random mutation
  • bacteria gaining advantageous allele and pass on
  • directional selection
• causes for antigen variability

  • dna base sequence change due to mutation
  • so difference codon sequence
  • different primary structure and tertiary structure
  • different antigen shape
• how does antigen variability affect getting disease?

  memory cells aren't complimentary to antigen anymore so no longer immune.
• What is primary resistance?


  structures which make bacteria resistant
• what is secondary resistance?


  bacteria that was once susceptible is now becoming resistant
• secondary resistance development


  • random mutation in dna
  • selection pressures
  • new advantageous allele
  • passed on to offspring
  • increased allele freuquency