Community-acquired pneumonia caused by mixed aerobic bacteria

Mixed bacterial pneumonia caused by organisms other than anaerobes has been infrequently reported. We describe six cases and review the literature. Two patients had co-infection with S pneumoniae and L pneumophila. Two were infected with S pneumoniae and K pneumoniae and the others simultaneously harbored M tuberculosis and N asteroides. The first two sets of patients had bacteria isolated from usually sterile sites (blood and lung), while the latter harbored repeatedly isolated organisms not usually felt to be part of the normal respiratory flora. Mixed infection may help explain the substantial mortality still seen from pneumonia. This is especially true if Legionella, mycobacteria, or Nocardia species are encountered where routine smears and cultures may not aid in the diagnosis. Poor clinical response to specific antibacterial therapy in pneumonia should trigger further investigation for other potential pathogens.