Nosocomial pneumonia is most commonly caused by:

Answer is A (Gram -ve bacilli): Nosocomial pneumonias are common in immunocompromised patients and are characterized by colorization of the nasopharynx by 'Grum negative bacilli' followed by trickling of upper airway secretions into lower airways, resulting in pneumonia' - `In a national survey in United States, 64% of all microorganisms isolated from the lungs of patients with nosocomial pneumonias were grant negative bacilli' - Remember: Changing trend: S. aureus (gram positive cocci) is the most common cause of nosocomial pneumonia in the United States - Harrison 16th/1539 Thus while overall gram negative bacilli are the most common of cumulative agents for nosocomial pneumonias, Staph aureus is the most common individual etiological agent