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?

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.