This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
[{'content': "Legionnaire's disease is caused most commonly by- \nSelect and explain. \nA. Legionella pneumophila, B. Legionella micdadei, C. Pittsburgh agent, D. None of the above", 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Legionella pneumophila * Most common species infecting man is L pneumophila (most common serogroup 1). Other important species is L. micdadei (Pittsburgh pneumonia agent) which is partial acid fast.* At least 14 serogroups of L. pneumophila have been identified.* L. pneumophila serogroup 1 (SG 1) accounts nearly all severe infections.* L. pneumophila serogroup 6 is more commonly involved in hospital - acquired legionnaire's disease.", 'role': 'assistant'}]