0908 - Infections of the Cardiorespiratory System Flashcards
What are the names and gram stain appearance of the 4 most common pathogens commonly associated with respiratory infections?
Strep. pneumoniae - Gram positive diplococci
Haemophilus Influenzae - Gram negative coccobacilli
Moraxella Catarrhalis - Gram negative diplococci (Upper respiratory tract)
Neisseria meningitidis - Gram negative diplococci (Lower respiratory tract)
What are the relevant virulence factors for Streptococcus pneumoniae?
KEY EXAM Concept - One example of impedin, aggressin, and modulin to illustrate pathophysiology of Sp Pneumoniae
The Capsule. Most important. Impedin as it confers resistance to phagocytosis, allowing more bacteria to survive and multiply. And 90 capsule types mean few opportunities for acquired immunity.
Capsule also generates the immune response (aggressin).
Adhesin proteins mediate adherence.
Cell lysis acts as an agressin. Cell wall components peptidoglycan, techoic acid, lipotechoic acid generate vigorous local inflammatory response. Pneumolysin is cytotoxic to endothelial cells via pneumolysin. Together they eliminate the muco-cilliary escalator and disrupt alveola-capillary boundary, facilitating transfer to bloodstream.
Lysis also acts as modulin - pneumolysin is cytotoxic to immune cells, and peptidases interfere with immune signalling.
What are the two most common sources of lower respiratory infection?
Endogenous (opportunistic) - normal flora take advantage of a breakdown in the muco-ciliary escalator to colonise normally sterile areas of respiratory tract (or eustacian tube).
Exogenous - purely pathogenic microorganism invades the body (e.g. shaking someones hand after they sneeze)
What are the clinical signs of Strep pneumoniae pneumonia?
Abrupt onset with high fever
Chest pain
Cough
Dyspnoea - shortness/difficulty and pain
Generally history of previous viral infection
Often over 65 or less than 5 years of age.
How does Strep. pneumoniae evade the primary, secondary, and tertiary immune responses?
Primary - breakdown in muco-ciliary escalator. Often caused by virus, but Sp can also do this once established.
Secondary - Capsule (impeden) gives resistance against phagocytosis and neutrophils. Pneumolysin (agressin) and cell wall components (agressin/modulin) induce vigorous immune response and cause local damage - facilitate disemination, further harm to muco-ciliary escalator, and spread to others.
Tertiary - Different capsule types evade acquired immunity.
How can Strep. Pneumonia lead to baceraemia and meningitis?
Once infection established, partial cell lysis releases pneumolysin. Cytotoxic to endothelial and immune cells, breaks down barrier between alveoli and capillaries. Haematogenous spread (bacteraemia). Sp has a tropism for CNS,
