Which gram-positive bacteria can cause bacterial pneumonia?

Updated: Oct 25, 2019
  • Author: Justina Gamache, MD; Chief Editor: Guy W Soo Hoo, MD, MPH  more...
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Answer

Although several of the organisms discussed in this section may be implicated in pneumonia, only a few of them are responsible for the vast majority of cases.

Gram-positive bacteria that can cause pneumonia include the following:

  • Streptococcus pneumoniae: This organism is a facultative anaerobe identified by its chainlike staining pattern. Pneumococcosis is by far the most common cause of typical bacterial pneumonia.

  • Staphylococcus aureus: S aureus is a facultative anaerobe identified by its clusterlike staining pattern. S aureus pneumonia is observed in intravenous drug abusers (IVDAs) and individuals with debilitating disorders. In patients who abuse intravenous drugs, the infection probably is spread hematogenously to the lungs from contaminated injection sites. Methicillin-resistant S aureus (MRSA) has had a large impact on empiric antibiotic choices at many institutions.

  • Enterococcus (E faecalis, E faecium): These organisms are group D streptococci that are well-known normal gut florae that can be identified by their pair-and-chain staining pattern. The emergence of vancomycin-resistant Enterococcus (VRE) is indicative of the importance of appropriate antibiotic use.

  • Actinomyces israelii: This is a beaded, filamentous anaerobic organism that grows as normal flora in the gastrointestinal (GI) tract and can colonize the oral cavity in patients with periodontal disease. A israelii is known to form abscesses and sulfur granules.

  • Nocardia asteroides: N asteroides is a weakly gram-positive, partially acid-fast bacillus (AFB) that forms beaded, branching, thin filaments. It is known to cause lung abscesses and cavitations. Erosion into the pleura can also occur, resulting in hematologic spread of the organism.


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