What are the most common organisms causing hospital acquired pneumonia ?

Most common organisms isolated from respiratory specimens of patients known or suspected to have HAP are Pseudomonas aeruginosa, Staphylococcal aureus and Enterobacteriaceae (especially Klebsiella, E. coli and Enterobacter spp.)

Pseudomonas aeruginosa is the most common organism causing hospital acquired pneumonia 

Staph aureus ,klebsiella, pseudomonas aeroginosa

P aeruginosa, staphylococcus aureus, and klebsiella pneumoniae

klebsilla pneumonae due to prolonged ventilation

Staphylococcus Aureus / P. aeruginosa

It develops at least 48h after hospital admission... The most common pathogens are gram-negative bacilli and Staphylococcus aureus.

48 hours after admission, hospital-acquired pneumonia may be acquired from gram-negative bacilli such as Staphylococcus aureus.

staphylococcus and pseudomonas bacteria

Common organisms: Pseudomonas aeruginosa, Klebsiella Pneumoniae, E. Coli, S. marcescene

Less common organisms: Legionella species, Viral Pneumonia

Unusual causes: Enterobacter, Staph. aureus

Staphylococcus aureus, including methicillin-susceptible S aureus (MSSA) and methicillin-resistant S aureus(MRSA) Klebsiella