Streptococcus cristatus: An uncommon cause for a common hospital admission

Common organisms associated with community-acquired pneumonia include Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus. Pneumonia can rarely be caused by an organism such as Streptococcus cristatus, as in our case. This organism belongs to the Mitis group within the Streptococcus genus and typically coexists with humans in the oral cavity. We present a case of Streptococcus cristatus bacteremia and community acquired pneumonia in a previously healthy 40-year-old male, for whom infective endocarditis has been ruled out, and who was successfully treated with ceftriaxone. While most reported cases of Streptococcus cristatus involve infective endocarditis, our case is the first identified instance of community acquired pneumonia caused by Streptococcus cristatus. This case highlights that pneumonia with Streptococcus cristatus, typically considered a commensal in the oral mucosa microbiota of humans, is possible, as seen in our case. Unlike previous cases in the literature, our patient did not have infective endocarditis, which is the common presentation of this bacterium. Instead, he solely presented with pneumonia, marking the first reported case in the literature of Streptococcus cristatus causing pneumonia.