Endocarditis Pathogenesis

Infective Endocarditis

• Coagulase-negative staphylococci are the most common cause of infective endocarditis (IE) on prosthetic heart valves.
• The pathogenesis of IE involves:
  • Colonization of mucous membranes and skin
  • Trauma resulting in bacteremia
  • Adherence of organisms to roughened endocardial surfaces
  • Promotion of adherence by fibrin, platelet aggregation, and endothelial damage
  • Platelet-fibrin deposition and bacterial division leading to vegetation development
  • Fragmentation of vegetations into the bloodstream, causing embolization of other organs
• Consequences of IE on the heart valves:
  • Cauliflower-shaped vegetations may develop, impairing valve function or breaking off into the systemic circulation
  • Ongoing inflammation may destroy the valve and cause valvular insufficiency
  • Small emboli may enter coronary arteries, causing myocardial infarction
  • Abscesses may develop in the heart muscle, impairing electrical conduction
• Consequences of IE in the brain:
  • Showering of the cortex with multiple micro-emboli, leading to confusion or coma
  • Large emboli may produce strokes or brain abscesses
  • Meningitis may occur from ongoing bacteremia or emboli
• Other consequences of IE:
  • Emboli may break off and obstruct renal arteries or cause kidney inflammation and damage
  • Emboli may also go to the spleen, extremities, eye, or other organs
  • Involved blood vessels may weaken, stretch, and burst

Bacterial Meningitis

• Pathogenesis:
  • Nasopharyngeal colonization
  • Local invasion
  • Bacteremia
  • Meningeal invasion
  • Bacterial replication in the subarachnoid space
  • Release of bacterial cell wall components
• Development of disease:
  • Release of bacterial cell components
  • Activation of macrophages to release cytokines
  • Subarachnoid space inflammation
  • Increased CSF outflow resistance
  • Cerebral vasculitis
  • Increased blood-brain barrier permeability
  • Increased brain edema
  • Confusion and coma
• Diagnosis:
  • Clinical features: headache, stiff neck, fever, and confusion
  • CT scan showing no evidence of a mass in the brain
  • Cloudy cerebral spinal fluid with increased numbers of white cells, high protein, and low glucose
  • Organisms seen on gram stain (may be negative if antibiotics have been administered)
  • CSF culture for bacteria, culture of blood also useful
  • PCR for bacteria in CSF may be used if cultures are negative
• Epidemiology:
  • Listeria monocytogenes affects the very young and the old (>50), often related to food outbreaks
  • Enteroviruses cause mild cases during summer and may occur in clusters
  • Arboviruses are seen primarily in localized areas where the virus, mosquitoes, and other hosts encounter optimal conditions

This quiz covers the formation of endocarditis, including the colonization of mucous membranes and skin, trauma, bacteremia, and the adherence of organisms to endocardial surfaces.