A patient presents with signs of pneumonia. The bacterium obtained from sputum was a gram-positive cocci which showed alpha hemolysis on sheep agar. Which of the following test will help to confirm the diagnosis?: (A) Bile solubility, (B) Coagulase test, (C) Bacitracin test, (D) CAMP test
Answer is A. S. pneumoniae, however, differs from streptococci in its morphology (by having a specific polysaccharide capsule), bile solubility, and optochin sensitivity.

S. pneumoniae produces an autolytic enzyme amidase, which solubilizes the peptidoglycan of the cell wall; hence in old cultures, typical draughtsman colonies are formed. This autolytic activity can be augmented by surface active agents, such as bile and bile salts.
Bile solubility is a constant feature of pneumococci, and is positive in all the capsulated and some noncapsulated variants.
Pneumococci are catalase and oxidase negative.

Parija SC. Textbook of Microbiology & Immunology. Elsevier Health Sciences; 2014. Page:194-95