A 70 years old patient presents with high grade fever, dry cough and abdominal pain. Sputum sample collected from patient, shows gram negative organisms that are able to grow only on charcoal yeast extract medium. The most likely organism is:

Ans. (b) Legionella Dry cough, high grade fever and growth on charcoal yeast medium suggest legionella. Legionella have fastidious requirements and grow on complex media such as buffered charcoal, yeast extract (BCYE) agar with L. cysteine and antibiotic supplements with 5% CO2 at pH 6.9, 35degC and 90% humidity.