The pneumococcus. Past, present and future

Streptococcus pneumoniae (Pneumococcus) is lancet-shaped, gram-positive, aerotolerant, facultative anaerobic organisms. Pneumococci are typically observed in pairs (diplococci) but may also occur singularly or in short chains. Almost all pneumococci are encapsulated, their surfaces being composed of complex polysaccharides. Encapsulated organisms are pathogenic for humans and laboratory animals, whereas organisms without capsular polysaccharides are not. Capsular polysaccharides are the primary basis for the pathogenicity of the organism. They are antigenic and their seroreactivity is the criterium for classifying pneumococci in serotypes.