Types of Bacteria That Cause Pneumonia

The most common types of bacteria that cause pneumonia are Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Chlamydia and Legionella pneumophila.

Streptococcus pneumoniae

• Streptococcus pneumoniae is a coccoid bacterium shaped like a lancet, being elongated and slightly curved. When it divides, Streptococcus pneumoniae generally forms groups of twos, although single bacteria and short chains may also form. Scientists can identify Streptococcus pneumoniae from its positive response to the Gram test (which indicates a high amount of peptidoglycan, a mesh-like substance that forms and strengthens the cell wall), its sensitivity to bile and the optochin chemical, and its reaction with red blood cells.

  According to the U.S. Centers for Disease Control (CDC), Streptococcus pneumoniae most commonly afflicts the elderly, infants, blacks, American Indians and Alaska natives. Other high-risk groups include those infected with HIV or sickle-cell disease.

Haemophilus influenzae

• Haemophilius influenzae is a pleomorphic bacterium, meaning it can assume different shapes. As a cocco-bacillus, it can appear as either a sphere or as a rod. It is non-motile, having no means of movement, and it responds negatively to the Gram test.

  Haemophilius influenzae is also a facultative anaerobe, which refers to its behavior in the presence of oxygen. Facultative anaerobes can grow with or without oxygen, but the less oxygen present, the more rapidly they grow.

  According to Vidya R. Devarajan, MD, the most infectious strain is H influenza type b (Hib). Hib disease occurs most commonly in Australian Aborigines, African Americans and American Indians.

Mycoplasma pneumoniae

• Mycoplasma pneumoniae are among the few bacteria that can live without a cell wall. These bacteria are pleomorphic, having a number of different shapes, even within the same environment. Additionally, they respond negatively to the Gram test, and as facultative anaerobes, they grow best where there is little or no oxygen. Mycoplasma pneumoniae are among the tiniest bacteria that can reproduce without a living host cell.

  Mycoplasma pneumoniae cause walking pneumonia. Walking pneumonia is less severe than other forms of the disease, and its symptoms resemble a nasty cold or flu, including fever, chills, rashes and body pains. Aside from bed rest, no additional treatment is generally needed.

Chlamydia

• Three members of the Chylamydia genus--Chlamydia trachomatis, Chalmydia pneumoniae and Chlamydia psittaci--cause pneumonia. Chlamydia trachomatis is a culprit behind infant pneumonia, which causes coughing and wheezing but generally no fever. Chlamydia pneumoniae and Chlamydia psittaci, on the other hand, are known to cause walking pneumonia.

  Because they contain little peptidoglycan, Chlamydia bacteria respond negatively to the Gram test. They also cannot produce their own energy, or adenosine triphosphate (ATP), making them "energy parasites" that require host cells for reproduction. For this reason, Chlamydia bacteria were once thought to be viruses.

  All three are cocci shaped and nonmotile.

Legionella pneumophilia

• Legionella pneumophilia is a pleomorphic bacteria common in watery environments. It is rod-shaped and motile by means of a single flagellum, and it responds negatively to the Gram test. Unlike other bacteria that cause pneumonia, Legionella pneumophilia is aerobic, meaning it requires the presence of oxygen to survive.

  Like Mycoplasma pneumoniae and the Chlamydia bacteria, Legionella pneumophilia causes walking pneumonia.