A person presents with pneumonia. His sputum was sent for culture. The bacteria obtained were gram-positive cocci in pairs and alpha hemolytic colonies on sheep agar. Which of the following will help in confirming the diagnosis

The pathogen is likely to be streptococcus pneumoniae, which is alpha hemolytic ( greenish discoloration due to incomplete hemolysis ) and gram-positive. Streptococcus pneumoniae is optochin sensitive. Optochin sensitivity: the sensitivity of Streptococcus pneumoniae to optochin is useful in differentiating it from other streptococci. When a disc impregnated with optochin is applied on a plate of blood agar inoculated with Streptococcus pneumoniae, a wide zone of inhibition appears on incubation. Reference: Textbook of Microbiology; Anathanarayan and panicker's; 10th edition; Page no: 223, 225