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: Medicine
A 60 year old male patient admitted in ICU develops fever and productive cough 48 hours after admission in the hospital. Which of the following is the most common causative organism? 
Select and explain. 
A. Mycoplasma, B. Pseudomonas, C. Staphylococcus, D. Hemophhilus Influenza
B: Pseudomonas
Answer: B: Pseudomonas 
Explanation: Hospital acquired pneumonia is polymicrobial in origin and is most commonly caused by gram negative bacilli such as Pseudomonas, Klebsiella and E coli. Other causative organisms inlcudes anaerobic bacteria and Staphyloccoccus aureus.