This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'Community acquired pneumonia is most commonly caused by: September 2005 and March 2008 \nSelect and explain. \nA. Staphylococcus aureus, B. Streptococcus pneumoniae, C. H.influenza, D. Klebsiella', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B: Streptococcus pneumoniae The term community-acquired pneumonia is usually reserved for people who have pneumonia caused by one of the more common bacteria or viruses. Streptococcus pneumonia is the most common cause of community-acquired acute pneumonia. Gram-negative rods (Enterobacteriaceae and Pseudomonas species) and S.aureus are the most common isolates in hospitalacquuired pneumonia; unlike community-acquired pneumonias, S.pneumoniae is not a major pathogen in hospitalacquuired pneumonia. Haemophilus influenzae, Chlamydia pneumoniae, and Mycobacterium pneumoniae are the other common bacterial causes. Common viral causes include respiratory syncytial virus (RSV), adenoviruses, influenza A and B viruses, metapneumovirus, and parainfluenza viruses.', 'role': 'assistant'}]