a.k.a. pneumonococcus.
Obligate parasite of human
Nasopharynx in carriers.
Droplets from nose in carriers.
Capsule is antiphagocytic (protection from PMN in absence of anti-capsular antibodies), and antigenic.
85 capsular serotypes, 20 of which accounts for majority of infections.
Peptidoglycan hydrolase in bacterial cell wall.
Normally inactive.
Can be triggered fo by surface-active agents, beta-lactam antibiotics, or aging.
Causes (s. pneumoniae) cell lysis, producing pneumolysin.
Normally within the cytosol of intact s. pneumoniae.
Released by autolysin.
Causes lysis by attacking mammalian cell membrane.
Most common cause of pneumonia and otitis media
More susceptible individuals - malnutrition, alcoholism, post viral respiratory infections, immunocompromised, sickle cell disease, splenectomy.
Often preceded by an upper respiratory viral infection.
-> due to increased volume and viscosity of secretion and inhibited action of bronchial cilia.
Most commonly caused by s. pneumoniae.
Other common causes are Haemophilus influenzae, and Moraxella catarrhalis
Haemophilus influenzae used to be the leading cause, until vaccination.
S. pneumoniae is the second most common cause.
Neisseria meningitidis is the most common cause.
Lancet-shaped, tend to occur in pairs.
Encapsulated.
alpha-hemolytic.
No Lancefield type group.
Growth inhibited by low concentrations of the surfactant, optochin.
Lysed by bile.
Capsular swells when treated with type-specific antisera (Quellung reaction)
First line: 3rd generation cephalosporins, e.g. cefotaxime, ceftriaxone
Second line: vancomycin
Resistence to penicillin G common.
PMN = polymorphonuclear leukocyte
Things to revise/add later:
Bibliography: LWW microbiology
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Created | 20040329 |