Unpredictable Virulence of a Benign Commensal: Streptococcus salivarius Bacteremia and Infective Endocarditis in an Immunocompetent Patient

Streptococcus salivarius is a gram-positive viridans group streptococcus that primarily colonizes the oral cavity and gastrointestinal tract and is generally regarded as a benign commensal organism. Although invasive infections have been reported, they typically occur in immunocompromised hosts or following invasive gastrointestinal or spinal procedures. We present a rare case of S. salivarius bacteremia complicated by meningitis and infective endocarditis in an elderly immunocompetent patient following a routine dental cleaning. A 74-year-old woman with a history of atrial fibrillation, hypertension, chronic obstructive pulmonary disease, and hypothyroidism presented with acute-onset severe headache, photophobia, nausea, and vomiting. Initial evaluation revealed leukocytosis and severe hypertension without focal neurological deficits. Within 24 hours, she developed acute encephalopathy. Blood cultures grew S. salivarius/vestibularis group. Cerebrospinal fluid analysis demonstrated marked neutrophilic pleocytosis and elevated protein, consistent with bacterial meningitis, though cultures were negative. Brain magnetic resonance imaging (MRI) raised concerns for purulent material, and computed tomography (CT) angiography revealed a small arterial communicating artery aneurysm. Transthoracic and transesophageal echocardiography identified mitral valve vegetation with moderate regurgitation, confirming infective endocarditis. The patient was treated with intravenous ceftriaxone with significant clinical improvement and eventual resolution of the vegetation on follow-up imaging. This case is notable for the occurrence of S. salivarius bacteremia and infective endocarditis in an elderly, immunocompetent patient, emphasizing that this organism, though typically nonpathogenic, can cause severe invasive disease even in the absence of traditional risk factors.