This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: FMGE 2019, Subject name: Pathology
MC cause of atypical pneumonia? 
Select and explain. 
A. Mycoplasma pneumoniae, B. Klebsiella pneumoniae, C. Hemophilus influenzae, D. Chylamydia
A: Mycoplasma pneumoniae
Answer: A: Mycoplasma pneumoniae 
Explanation: MC cause of Atypical pneumonia- Mycoplasma Pneumoniae aka "Eaton's agent". This organism does not have cell wall which makes them resistant to the treatment by Penicillin's. The infection will be treated by the use of Macrolide antibiotic (Azithromycin).