<prompt> An elderly male presented with fever, dry cough and chest pain. The causative organism was detected in sputum which is cultured on charcoal yeast medium. The organism is:H. influenzaeMoraxella catarrhalisLegionellaBurkholderia cepacia  <response>: This is a case of Legionella infection. The established approach to diagnosis combines direct fluorescent antibody DFA with culture of infected tissues. Cultures must be made on buffered charcoal yeast extract BCYE agar medium that includes supplements amino acids, vitamins, L-cysteine, ferric pyrophosphate, which meets the growth requirements of Legionella. It is buffered to meet the acidic conditions--optimal for Legionella growth pH 6.9. The isolation of large Gram-negative rods on BCYE after 2 to 5 days that have failed to grow on routine media blood agar, chocolate agar is presumptive evidence for Legionella. Diagnosis is confirmed by DFA staining of bacterial smears prepared from the colonies. Ref: Ray C.G., Ryan K.J. 2010. Chapter 34. Legionella. In C.G. Ray, K.J. Ryan Eds, Sherris Medical Microbiology, 5e. 