This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacterial infection, Subject name: Medicine
[{'content': 'Best test for mycoplasma infection is? \nSelect and explain. \nA. PCR of respiratory secretions, B. Gram stain of transtracheal aspirate, C. Culture of transtracheal aspirate, D. CXR', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Acute M. pneumoniae infection can be diagnosed by PCR detection of the organism in respiratory tract secretions. Oropharyngeal, nasopharyngeal, and pulmonary specimens are all acceptable for diagnosing M. pneumoniae pneumonia. M. pneumoniae culture requiring special media is not recommended for routine diagnosis because the organism may take weeks to grow and is often difficult to isolate from clinical specimens. In contrast, PCR allows rapid, specific diagnosis earlier in the course of clinical illness.', 'role': 'assistant'}]