Pneumococcus can be differentiated from streptococcus by

Bile solubility test: Streptococcus pneumoniae are bile soluble. If a few drops of 10% sodium deoxycholate solution are added to 1 ml of an overnight broth culture, the culture clears due to the Lysis of cocci. Alternatively, if a loopful of 10 % deoxycholate solution is placed on a Streptococcus pneumoniae colony on blood agar, the colony lyses within a few minutes. Bile solubility is a constant propey of Streptococcus pneumoniae and is of diagnostic impoance from other streptococci. The test should be carried out at neutral PH using deoxycholate and living young cells in saline suspension. Principal: based on the presence of an autolytic amidase in Streptococcus pneumoniae that cleaves the bond between an alanine and muramic acid in the peptidoglycan. The amidase is activated by surface active agents such as bile or bile salts. Reference: Textbook of Microbiology; Anathanarayan and panicker's; 10th edition; Page no: 224