Streptococcus pneumoniae Essay Example | Topics and Well Written Essays - 500 words

Streptococcus pneumoniae - Essay Example They are readily stained with aniline dyes and are Gram positive. The capsule may be demonstrated as a clear halo. They have complex growth requirements and grow only in enriched media. They are aerobes and facultative anaerobes, the optimum temperature being 37Â ºC. On blood agar after incubation for 18 hours, the colonies are small, dome shaped and glistening with an area of green discoloration along them. Some strains that develop abundant capsular material (types 3 and 7) form large mucoid colonies. Under anaerobic conditions, colonies on blood agar are surrounded by a zone of beta hemolysis due to oxygen labile hemolysin O. In liquid media, such as glucose broth, growth occurs as uniform turbidity. Streptoccocus pneumoniae ferment several sugars, forming acid only. Fermentation is tested in Hiss’s serum water or aerum agar slopes. They are bile soluble. Bile solubility is a constant property and hence is of diagnostic importance. Pneumococci are catalase and oxidase nega tive. They are delicate organisms and are readily destroyed by heat and antiseptics. The most important anitigen of pneumococcus is the type specific capsular polysaccharide. Pneumococci isolated from lobar pneumonia were originally classified into 3 types, I, II, and III and a heterogenous group IV. Memebers of Group IV were later classified into types, and 90 different serotypes are recognized. Typing may be carried out by i) agglutination of the cocci with a type specific antiserum; ii) precipitation of the SSS with the specific antiserum; or iii) the capsule swelling reaction described by Neufeld (1902). An abnormal protein (beta globulin) that precipitates with the somatic ‘C’ antigen of the pneumonia, appears in the acute phase sera of cases of pneumonia but disappears during convalescence. On repeated subculture, pneumococci undergo a smooth-to-rough (S-R) variation. The virulence of pneumococci depends on its capsule and the production of called