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: (A) Novobiocin, (B) Optochin, (C) Bacitracin, (D) Oxacillin
Answer is B. 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