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:

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.