Key definitions

• Virulence: the capacity of a microbe to cause damage to its host
• Pathogen: a harmful organism that produces a pathology
• Commensal: an organism that is part of the normal flora
  • Often a mutualistic relationship
  • Endogenous
• Opportunistic pathogen: an organism that causes infection when opportunity/change in natural immunity arises
• Coagulase test: use to differentiate between Staph. aureus and coagulase negative Staph. (including Staph epidermis)
• Haemolysis: used to differentiate between Streptococci

Sepsis

• Small blood vessels become ‘leaky’ and loose fluid into tissues - decreased blood volume so heart has to work harder
• Poor tissue perfusion means blood supply to less essential organs is shut down
• Blood clotting system activated - uses all clotting factors, increasing risk of haemorrhage
• Patients with Gram-negative sepsis get very unwell very quickly due to endotoxin released when Gram-negative bacteria die

Fever

1. Antigen/LPS interacts with macrophages
2. Macrophages release cytokines into bloodstream
3. Cytokines travel to anterior hypothalamus
4. Prostaglandin E released - increases body’s thermal set point
5. Body perceives it as cold - starts to ‘shiver’
6. FEVER

Key gram-negative pathogens