Gram-positive
Streptococcus pneumoniae
Staphylococcus aureus
Gram-negative
Haemophilus influenzae
Klebsiella pneumoniae
Escherichia coli
Pseudomonas aeruginosa 
Moraxella catarrhalis
Atypical pneumonia<unk>  pneumoniae<unk> 
Mycoplasma pneumoniae
Coxiella burnetti 
Legionella pneumophila
Streptococcus pneumoniae
Staphylococcus aureus
Haemophilus influenzae
Klebsiella pneumoniae
Escherichia coli
Pseudomonas aeruginosa 
Moraxella catarrhalis<unk>  pneumoniae<unk> 
Mycoplasma pneumoniae
Coxiella burnetti 
Legionella pneumophila
Common
Influenza
Respiratory syncytial virus
Parainfluenza
Rarer
Adenovirus
Metapneumovirus
Severe acute respiratory syndrome (SARS)
Middle east respiratory syndrome coronavirus (MERS)
2019-nCoV (COVID-19)
Cause other diseases, but sometimes cause pneumonia
Herpes simplex virus
Varicella-zoster (VZV)
Measles
Rubella
Cytomegalovirus
Smallpox
Dengue
Influenza
Respiratory syncytial virus
Parainfluenza
Adenovirus
Metapneumovirus
Severe acute respiratory syndrome (SARS)
Middle east respiratory syndrome coronavirus (MERS)
2019-nCoV (COVID-19)
Herpes simplex virus
Varicella-zoster (VZV)
Measles
Rubella
Cytomegalovirus
Smallpox
Dengue
Histoplasmosis
Coccidioidomycosis
Blastomycosis
Pneumocystis jirovecii pneumonia (PCP)
Sporotrichosis
Cryptococcosis
Aspergillosis
Candidiasis
Ascariasis
Schistosomiasis
Toxoplasma gondii<unk> sis
Anthrax (Bacillus anthracis)
Brucellosis (Brucella species)
Q fever (C. burnetti)
Pasteurellosis (Pasteurella multocida)
Melioidosis (Burkholderia pseudomallei)
Rocky Mountain Spotted Fever (R. rickettsii)
Pulmonic Plague (Yersinia pestis)
Influenza A
Hantavirus
Chlamydophila psittaci
Gram-positive
Chlamydophila pneumoniae
Streptococcus pneumoniae
Mycobacterium marinum
Staphylococcus aureus
Chlamydia trachomatis
Gram-negative