|
Bacteria are the most common causes of pneumonia, but these infections can also be caused by other microbial organisms. It is often impossible to identify the specific culprit bacteria. Many bacteria are categorized by the staining procedure used to visualize bacteria under a microscope. The stains determine if they are gram-negative or gram-positive bacteria. This gives the physician an idea of the severity of the pneumonia and how to treat it.
Gram-Positive Bacteria: These bacteria appear blue on the stain. The following are common gram-positive bacteria:
- The most common cause of pneumonia is the gram-positive bacterium Streptococcus pneumoniae (also called S. pneumoniae or pneumococcal pneumonia ). It was thought to cause 95% of community-acquired bacterial infection, but research now indicates it is far less, accounting for about half of all cases. (Some studies suggest it may account for even fewer, 10% to 30% of cases.)
- Staphylococcus aureus , the other major gram-positive bacterium responsible for pneumonia, accounts for about 10% of bacterial cases. It is one of the main causes of pneumonia that occurs in the hospital (nosocomial pneumonia). It is uncommon in healthy adults but can develop about five days after viral influenza, usually in susceptible individuals, such as people with weakened immune systems, very young children, hospitalized patients, and drug abusers who use needles.
- Streptococcus pyogenes or Group A Streptococcus.
Gram-Negative Bacteria: These bacteria stain pink . Gram negative bacteria are common infectious agents in hospitalized or nursing home patients, children with cystic fibrosis, and people with chronic lung conditions.
- The most common gram-negative species causing pneumonia is Haemophilus influenzae (generally occurring in patients with chronic lung disease, older patients, and alcoholics).
- Klebsiella pneumoniae may be responsible for pneumonia in alcoholics and in other people who are physically debilitated.
- Pseudomonas aeruginosa is a major cause of pneumonia that occurs in the hospital (nosocomial pneumonia). It is common in pneumonia patients with chronic or severe lung disease.
- Moraxella catarrhalis is found in everyone's nasal and oral passages. Experts have identified this bacteria as a cause of certain pneumonias, particularly in people with lung problems, such as asthma or emphysema.
- Neisseria meningitidis is one of the most common causes of meningitis (central nervous system infection), but the organism has been reported in pneumonia, particularly in epidemics of military recruits.
- Other gram-negative bacteria that cause pneumonia include E. coli (a cause in newborns), Proteus (found in several damaged lung tissue), and Enterobacter.
Infection with the Streptococcus pneumoniae bacterium, also called pneumococcus, is the most common cause of bacterial pneumonia. Pneumococcus usually causes lobar pneumonia, attacking an entire lobe or portion of a lobe of the lung; in double pneumonia, pneumococcus attacks both lungs. Pneumococcal lobar pneumonia often occurs in winter after an acute, viral upper respiratory infection. Usual symptoms include a shaking chill followed by a fever of about 40°C (104°F), pain in the chest while breathing, a cough, and blood-streaked sputum.
Other bacteria that cause pneumonia include Klebsiella pneumoniae, Haemophilus influenzae, Legionella pneumophilia (the bacterium that causes Legionnaires' disease), and various staphylococci and streptococci bacteria. Infections with these organisms primarily cause bronchopneumonia. Onset of symptoms is generally slower than with lobar pneumonia, and the fever is lower.
|
