STREPTOCOCCUS PNEUMONIAE "PNEUMOCOCCUS"

STREPTOCOCCUS PNEUMONIAE "PNEUMOCOCCUS"      The pneumococcus is carried in the nasopharynx by many healthy persons. The carrier rate varies between different population groups and between different times in the same group but most commonly ranges between 10 and 30%. Morphology:      The pneumococci are Gram-positive diplococci; often lanceolated with their distal ends narrowed. They are non-sporing, possessing a capsule of polysaccharide that permit typing with specific antisera. Cultural Characters:      Aerobe andfacultative anaerobe, optimum temperature for growth is 37°C. Does not grow on nutrient agar or MacConkey's agar, but grows on media containing 5-10% serum or blood. Colonies on blood agar are small (1 mm in diameter), smooth, low convex, transparent and α-haemolytic. With prolonged incubation the colonies become flattened or depressed centrally (draughtsman form). Different Characters Of Pneumococci And Viridans Streptococci:   Character Pneumococci Viridans Streptococci Morphology: Ovoid or lanceolated diplococci; short chains Short or long chains of rounded cocci Capsule: Present Usually absent Colonies: Become flattened or draughtsman form convex Optochin sensitivity: Sensitive Resistant Bile solubility: + - Inulin fermentation: + - Virulence in mice: + - Antigenic Structure:      Eighty three serotypes of pneumococci are distinguished by differences in the nature of the polysaccharide antigen that composes their capsules. The type of a Pneumococcus is determined by its reaction with type-specific antisera.      The test may be done by Neufeld's "quellung" or "swelling" reaction. When pneumococci of a certain type are mixed with specific antipolysaccharide serum of the same type (or with polyvalent antiserum) on a microscope slide, the capsule swells markedly. This reaction is usefull for rapid identification and for typing of the organisms, either in sputum or from culture. Pathogenesis:      The pneumococcus generally remains harmless in the carrier unless it is provoked by a viral infection such as influenza virus (secondary pathogen). They are the commonest bacterial pathogens in lobar and broncho-pneumonia and its complications like pleurisy, empyema, meningitis, arthritis, sinusitis, and brain abcess. Pneumococci produce disease through their ability to multiply in the tissues. They produce no toxins. The virulence of the organism is a function of its capsule which delays their phagocytosis. The organism may reach the blood stream via the lymphatic drainage of the lung (bacteraemia). Laboratory Diagnosis: Specimen:      May be either blood (bacteraemia), CSF (meningitis) and sputum (bronchopneumonia). Direct smears:      A Gram stained smear of sputum (or exudate or CSF) shows Gram-positive lanceolated diplococci and many polymorphonuclear leukocytes. Culture:      Specimen is cultured on blood agar and incubated aerobically + 5-10% CO2.      The isolated α-haemolytic colonies must be distinguished from viridans streptococci by optochin test, bile solubility test and inulin fermentation. Animal Pathogenicity Test:      Intraperitoneal injection of sputum into mice, the animals die in 18-48 hours; heart blood gives pure culture of pneumococci. Capsule Swelling Test:      It is useful for rapid identification and for typing of pneumococci in sputum or from culture.

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