A 70 year old man presents with complaints of chest pain, fever, cough with sputum. On examination of sputum pus cells with gram positive cocci are present. Blood agar showed positive result. How will you differentiate this from other gram positive cocci?

Pneumococci 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 pneumococcus colony on blood agar the colony lysis within a few minutes. Bile solubility is a constant propey of pneumococci and hence is of diagnostic impoance. The bile solubility test is based on the presence in the pneumococci of an autolytic amidase that cleaves the bond between alanine and muramic acid in the peptidoglycan. The amidase is activated by surface active agents such as bile / bile salts, resulting in lysis of the organisms. Ref: Ananthanarayanan & Paniker's textbook of microbiology Ed 8 Pg - 219.