2.01 - Infections Of The Cardiorespiratory System Flashcards
Describe the basic features of Steptococcus pyogenes
Gram positive Chains Beta-haemolytic Group A Strep Mesophile Growth at neutral-slightly acidic pH
Why is the URT good for bacterial growth
Rich in nutrients: mucus, fluids, food
Predominantly aerobic
Body temperate
Neutral to slightly acidic pH
Describe the MCCE
The mucociliary escalator
Helps keep the lung sterile. Traps small particles we breathe. Mucous bounds particles are swept out by cilia (which cycle synchronously, continuously)
Describe the basic features of streptococcus pneumoniae
Gram positive Diplococci Alpha-haemolytic Aerobic Aerotolerant Part of the commensal flora of the URT
Describe the role of S. pneumoniae in the pathogenesis of the two major infections it can cause
• Infection of eustachian tube –> presence of Sp attracts
polymorphonuclear leukocytes (PMN) Sp resistant to phagocytosis
• Infection of lung –> Presence of Sp attracts alveolar macrophages. Sp resistant to phagocytosis.
Describe bacterial capsules
Capsules are comprised of repeating polysaccharide units that covers peptidoglycan cell wall
What are some common capsulated bacteria?
Haemophilus influenzae
Neisseria meningitidis
Streptococcus pneumoniae
What type of virulence factor are capsules
Impedins
They confer resistance to an important innate immune function, phagocytosis
When bacteria grow, a few bacterial cells will lyse. What is the consequence of this with regards to the immune system?
Lysis of S. pneumoniae releases cell wall components, leading to a vigorous local inflammatory response These components include: Peptidoglycan Techoic Acid Lipotechoic Acid
When S. pneumoniae cells lyse the release an aggression. What is it and what does it to to aid in the infective process?
Pneumolysin
It is cytotoxic to endothelial cells, so contributes directly to tissue damage. It eliminates the function of ciliated epithelium and disrupts the alveolar-capillary boundary and facilitates transfer to the bloodstream –> dissemination of infection. It is also cytotoxic to immune cells
What are some symptoms of pneumonia caused by S. pneumoniae?
Abrupt onset with high fever Chest pain Cough Shortness of breath Difficulty and pain on breathing
What are the methods of bacterial dissemination?
Physical mechanisms such as trauma
Intra- and intercellular spread
Infection of macrophages and spread through lymphatics
Haematogenous spread
Immunological
Local and systemic dissemination of bacterial toxins
Summarise the pathogenesis of S. pneumoniae
Endogenous entry
S. pneumoniae is part of the commensal microflora of upper respiratory tract where adhesins contribute to colonisation
When primary defense – mucociliary escalator – inhibited, Sp colonises sterile areas of upper/lower respiratory tract
Extracellular Replication
Capsule (Impedin) – confers resistance against secondary
defenses (phagocytes/PMNs)
Pneumolysin (aggressin) and cell wall components
(aggressins/modulins)
