Last reviewed 01/2018

Pneumococcus is probably the most common and most important pathogen amongst the streptococci. It is a normal commensal of the upper respiratory tract.

Pneumococcus is a Gram-positive lanceolate diplococcus with an antigenic carbohydrate capsule which conveys virulence.

Pneumococcus shows alpha haemolytic activity but is distinguished from viridans streptococci by draughtsman / mucoid colonies, optochrin sensitivity and bile solubility.

Pneumococcus is not Lancefield groupable (1)


  • Tuomanen EI et al (1995). Pathogenesis of pneumococcal infection. NEJM, 332, 1280-2.