<unk>  is an infection of the lungs by<unk> 
Streptococcus pneumoniae is the most common<unk>  cause of pneumonia in all age groups except newborn infants. Streptococcus pneumoniae is a gram-positive<unk> which often lives in the throat of people who do not have pneumonia. Another important gram-positive cause of pneumonia is Staphylococcus aureus.
Gram-negative<unk> are seen less frequently; Haemophilus influenzae, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa and Moraxella catarrhalis are the most common. These<unk> often live in the gut and enter the lungs when contents of the gut (such as vomit) are inhaled.
The "atypical"<unk> are Coxiella burnetti, Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila. They are "atypical" because they commonly affect teenagers and young adults, are less severe, and require different antibiotics than typical<unk> such as Streptococcus pneumoniae.
Bacterial pneumonia
Viral pneumonia
Fungal pneumonia
Atypical pneumonia
Community acquired pneumonia
Community-acquired pneumonia
Aspiration pneumonia
Hospital-acquired pneumonia