Streptococcus pneumoniae is a gram positive bacterium that is responsible for the majority of pneumonia which is acquired from community.
Characterestics
# cells are gram positive . # lancet shaped cocci
# diplococci ( usually they are seen as a pairs of cocci) # they may also occurs singly and in short chains.
# in blood agar culture, they are alpha hemolytic #individual cells are between 0.5 and 1.25 micrometers in diameter.
# they do not form spores # they are nonmotile. # the do not display M protein and they hydrolyse insulin.
Nutritional factors
Streptococcus pneumoniae relies carbohydrates as a carbon source and devotes thirty percent of all transport mechanisms to carbohydrate import.
Virulence factors
Capsule is the major virulence factor of streptococcus pneumonia resistance to phagocytosis. ' cell wall 'is also playing an important role as a virulence factor.
# activation of the alternative compliment pathway resulting an anaphylatoxin production. During complement activation, the anaphylatoxins C3a and C5a which enhance vascular permiability. Induce mast cell degranulation and recruit and activate polymorphonuclear leukocytes at the inflammation site.
Epidemiology
# s. pneumonia colonise in nasopharynx. They are transmitted by contaminated droplet . # dissemination is facilitated by crowding. # disease result only when host resistance is lowered by vural infections, pulmonary congestions,stress,malnutrition,immunodeficiency.
#splenectomy and sickle cell disease are important predisposing factor.
# type 3 is the most virulent
susceptibility to antibiotics.
Resistance to penicillin and cephalosporin. Most patients with mild or moderate pneumococcal pneumonia may respond to oral amoxicillin and most of with severe Pneumonia may be successfully treated with intravenous ceftriaxone, cefotaxim, or amoxicillin - clavulanic acid.
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