Systemic Bacteriology I

Key bacterial features

Shapes

  • Coccus/Cocci: spheres
  • Bacillus/Bacilli: rod shaped
  • Vibrio: slightly curved rod, gram-negative
  • Spirillum: rigid spiral bacterium
  • Spirochaete: flexible spiral bacterium

Defensive structures

  • Spore: inert structures, resistant to physical and chemical challenge
  • Capsule: outermost layer found in many bacteria, usually made of polysaccharides

Toxin

  • Promotes infection and disease by directly damaging host tissues and disabling the immune system

Aerobes and anaerobes

  • Aerobic: grow in oxygen
  • Obligate aerobes: require oxygen
  • Obligate anaerobes: killed by oxygen
  • Facultative anaerobes: tolerate oxygen

Identification of bacteria

  • Selective media: presence of specific substances permits the growth of one organism over another
  • Differential media: incorporation of chemicals produces visible changes in colonies that facilitates identification
  • Metabolic profiling: uses biochemical characteristics e.g. utilization of carbon sources
  • Serological tests: use an antibody-antigen interaction to help identify bacteria
  • DNA technology - genome sequencing
    • PCR: amplification of a section of genome
    • MLST: entire genome sequencing
  • MALDI-TOF: produces a characteristic signature based on the generation of ions from a sample (dependent on constituent proteins)