Definition: - Gram positive diplococci, often lancet shaped or arranged in chains, possessing a capsule of polysaccharides.
- Normal inhabitant of the throat and nasopharynx in healthy people.
- Leading cause of morbidity and mortality in persons of all ages.
- It is the most common cause of bacterial pneumonia and an important cause of otitis media, meningitis and septicaemia.
- S. pneumoniae - encapsulated gram-positive cocci, oval or spherical: - 0.5 - 1.2 µm diameter. - Lancet shaped, in pair or singles. - Pneumococci are very sensitive to the product of their fermentative metabolism, which result in Gram-negative reaction in older cultures. - Capsule readily demonstrated using India ink or use of homologous type-specific antibody in the Quellung reaction. - Smooth to rough variation (transformation) occurs in culture in presence of homologous antisera.
Not so well understood. The disease manifestations are caused primarily by host response to infection mainly in a form of inflammatory reaction mediated by pneumococcal antigens stimulating the complement system.
- Polyssacharide capsule inhibit phagocytosis
Smooth strains are highly virulent compared to rough strains which are easily phagocytosed.
Adherence - S pneumoniae attaches to the nasopharynx or the inner ear by interacting with the N-acetyl-glucosamine-galactose moiety of the cell surface glycolipid.
- In studies on the adhesin of S. pneumonia to human pharyngeal cells, differences observed between the adhesive capacities of the various strains could be correlated with the clinical origin of the strain.
1) Optochin sensitivity (Ethyl hydrocuprein hydrochloride) disk method.
2) Bile solubility - amidase is produced by pneumococci when stimulated by surface agents e.g. bile or bile salts - cleaves the bond between alanine and muramic acid in the peptidoglycan. This leads to lysis of the organism. Needs a neutral pH, 1% desoxycholate and viable young organisms.
Immunity: In adults natural immunity is high, without treatment 70% of pts recover. Type specific immunity to pneumococcal infection is long lasting.
Pneumococcal conjugate vaccine - using conjugate polyvalent vaccine with capsular polysacharides (23 types) which protects against 90% of pneumococcal infections. Efficacy 80-95%.
Indications -All pts at an increased risk of developing pneumococcal pneumonia
Those who have poor immunologic ability to respond to polysaccharides Ag to produces homotypic antibodies e.g chronic cardiac or respiratory diseases, SCD, Spleen hypofunction or asplenia, liver cirrhosis, DM, and chronic renal disease and Elderly.