Pneumococcus

• pneumococcus (Streptococcus pneumoniae) is widely considered the most common and clinically significant pathogen among the streptococci
• acts as a normal commensal organism residing in the human upper respiratory tract
• microbiologically characterized as a Gram-positive, lanceolate-shaped diplococcus protected by an antigenic carbohydrate capsule that serves as its key virulence factor
• exhibits alpha-haemolytic activity on blood agar, but is distinguished from viridans group streptococci by optochin sensitivity, bile solubility, and characteristic draughtsman/mucoid colony morphology
• does not possess a specific Lancefield cell wall carbohydrate antigen and is therefore not Lancefield groupable

Reference:

1. Fry NK et al. The pneumococcus and its critical role in public health. Methods Mol Biol. 2019;1968:205-213.