Polymicrobial <i>Streptococcus mitis</i> and <i>Vagococcus fluvialis</i> infective endocarditis

Background: Infective endocarditis (IE) is a life-threatening condition most commonly caused by Staphylococcus aureus, but other pathogens, including Streptococcus species, are increasingly recognized. The International Society for Cardiovascular Infectious Diseases (ISCVID) recently updated the list of “typical” IE pathogens, yet Vagococcus species remain excluded. This report aims to highlight the clinical significance of Vagococcus fluvialis in IE, addressing whether its isolation from blood cultures should prompt suspicion for endocarditis. Methods: We describe a case of polymicrobial IE in a man in his late 40s with a history of intravenous drug use and poor dentition. The patient presented with heart failure and a new diastolic murmur. Blood cultures grew Streptococcus mitis and V. fluvialis, identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and confirmed by 16S ribosomal RNA (rRNA) sequencing. Echocardiography revealed a large aortic valve vegetation and severe insufficiency. The patient underwent emergent aortic valve replacement and aortic root repair, followed by a 6-week course of intravenous ceftriaxone. Outcome measures included clinical recovery, echocardiographic findings, and microbiological clearance. Results: Both organisms were isolated from two sets of blood cultures. The patient experienced acute decompensation requiring intubation and surgery. Post-operatively, the ejection fraction was reduced (31%). Blood cultures cleared after initiation of antibiotics; the patient completed therapy in hospital and was discharged in good condition, though follow-up was limited by non-adherence. Conclusion: V. fluvialis bacteremia has been associated with IE in several published clinical case reports and may present with fulminant clinical courses. Its exclusion from current IE diagnostic criteria may contribute to underrecognition. Further surveillance and reporting are warranted.