Bacterial pneumonia

Bacterial pneumonia
Classification and external resources
Specialty Infectious disease
ICD-10 J13-J16
ICD-9-CM 481-483
eMedicine emerg/465
MeSH D018410

Bacterial pneumonia is a type of pneumonia caused by bacterial infection.[1]

Signs and symptoms



Streptococcus pneumoniae (J13) is the most common bacterial cause of pneumonia in all age groups except newborn infants. Streptococcus pneumoniae is a Gram-positive bacterium that often lives in the throat of people who do not have pneumonia.

Other important Gram-positive causes of pneumonia are Staphylococcus aureus (J15.2) and Bacillus anthracis.


Gram-negative bacteria are seen less frequently: Haemophilus influenzae (J14), Klebsiella pneumoniae (J15.0), Escherichia coli (J15.5), Pseudomonas aeruginosa (J15.1), Bordetella pertussis, and Moraxella catarrhalis are the most common.

These bacteria often live in the gut and enter the lungs when contents of the gut (such as vomit or faeces) are inhaled.


"Atypical" bacteria are Coxiella burnetii, Chlamydophila pneumoniae (J16.0), Mycoplasma pneumoniae (J15.7), and Legionella pneumophila.

Many people falsely believe they are called "atypical" because they are uncommon and/or do not respond to common antibiotics and/or cause atypical symptoms. In reality, they are "atypical" because they do not gram stain as well as gram-negative and gram-positive organisms.

Pneumonia caused by Yersinia pestis is usually called pneumonic plague.


Bacteria typically enter the lung with inhalation, though they can reach the lung through the bloodstream if other parts of the body are infected. Often, bacteria live in parts of the upper respiratory tract and are continuously being inhaled into the alveoli. Once inside the alveoli, bacteria travel into the spaces between the cells and also between adjacent alveoli through connecting pores. This invasion triggers the immune system to respond by sending white blood cells responsible for attacking microorganisms (neutrophils) to the lungs. The neutrophils engulf and kill the offending organisms but also release cytokines that result in a general activation of the immune system. This results in the fever, chills, and fatigue common in bacterial and fungal pneumonia. The neutrophils, bacteria, and fluid leaked from surrounding blood vessels fill the alveoli and result in impaired oxygen transportation.

Bacteria often travel from the lung into the blood stream (bacteremia) and can result in serious illness such as sepsis and eventually septic shock, in which there is low blood pressure leading to damage in multiple parts of the body including the brain, kidney, and heart. They can also travel to the area between the lungs and the chest wall, called the pleural cavity.


Antibiotics are the treatment of choice for bacterial pneumonia and ventilation (oxygen supplement) as supportive therapy. The antibiotic choice depends on the nature of the pneumonia, the microorganisms most commonly causing pneumonia in the geographical region, and the immune status and underlying health of the individual. In the United Kingdom, amoxicillin is used as first-line therapy in the vast majority of patients acquiring pneumonia in the community, sometimes with added clarithromycin. In North America, where the "atypical" forms of community-acquired pneumonia are becoming more common, clarithromycin, azithromycin, or fluoroquinolones as single therapy, have displaced the amoxicillin as first-line therapy. Local patterns of antibiotic-resistance should always be considered when initiating pharmacotherapy. In hospitalized individuals or those with immune deficiencies, local guidelines determine the selection of antibiotics.

Gram-positive organisms

Streptococcus pneumoniae — amoxicillin (or erythromycin in patients allergic to penicillin); cefuroxime and erythromycin in severe cases. Staphylococcus aureusflucloxacillin (to counteract the organism's β-lactamase).

Gram-negative organisms

Atypical organisms

People who have difficulty breathing due to pneumonia may require extra oxygen. An extremely sick individual may require artificial ventilation and intensive care as life-saving measures while his or her immune system fights off the infectious cause with the help of antibiotics and other drugs.


Prevention of bacterial pneumonia is by vaccination against streptococcus pneumoniae (pneumococcal polysaccharide vaccine for adults and pneumococcal conjugate vaccine for children), Haemophilus influenzae type B, meningococcus, bordetella pertussis, bacillus anthracis, and yersinia pestis.


  1. "bacterial pneumonia" at Dorland's Medical Dictionary
  2. "Bacterial Pneumonia". Lung Disease & Respiratory Health Center. WebMD. p. 2.
  3. Corey, Ralph (1990). "Ch. 39: Hemoptysis". In Walker HK, Hall WD, Hurst JW. Clinical Methods: The History, Physical, and Laboratory Examinations (3rd ed.). Boston: Butterworths. ISBN 0-409-90077-X.

External links

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