Most common cause of pneumonia:

  1. Community acquired
    a) Typical pneumonia is due to Streptococcus pneumoniae > Hemophilus influenzae.
    b) Atypical pneumonia is due to Mycoplasma > Chlamydia.

  2. Nosocomial is due to gram negative rods e.g. Enterobacteriaceae (E.coli and Klebsiella)

  3. Aspiration pneumonia is due to Anaerobic infections (Peptostreptococcus, Bacteroides, Prevotella, and Fusobacterium).

  4. With underlying Chronic alcoholism and COPD is due to Klebsiella pneumoniae.

  5. With underlying Bronchiectasis and cystic fibrosis is due to Pseudomonas aeruginosa.

  6. Ventilator associated pneumonia is due to Pseudomonas aeruginos