Abstract
BACKGROUND: Staphylococcus saccharolyticus is an obligate anaerobic skin commensal that is rarely implicated in bloodstream infections, particularly in immunocompetent individuals without implanted medical devices. Due to its low virulence and fastidious growth requirements, it is often overlooked or dismissed as a contaminant. This report describes a rare case of S. saccharolyticus bacteremia and explores the underlying pathogenic mechanism. CASE PRESENTATION: A 50-year-old immunocompetent female presented with recurrent low-grade fever and oral mucosal ulceration. Pathogen detection was performed using plasma-based metagenomic next-generation sequencing (mNGS), which identified S. saccharolyticus at a relative abundance of 15 % (seven species-specific reads). The result was corroborated by anaerobic blood culture. Laboratory assessment revealed severe vitamin D deficiency (25-hydroxyvitamin D: 11.6 ng/mL). Initial treatment with ceftriaxone was ineffective. Following the initiation of intravenous moxifloxacin and oral vitamin D supplementation (cholecalciferol 2000 IU/day), the patient's fever resolved within five days, and high-sensitivity C-reactive protein (hsCRP) levels decreased markedly from 88.3 mg/L to 12.0 mg/L. Mechanistically, the combination of mucosal barrier disruption due to oral ulceration and vitamin D deficiency may have facilitated translocation of the anaerobic pathogen into the bloodstream. CONCLUSIONS: This case underscores the diagnostic value of mNGS in detecting low-biomass anaerobic infections and proposes a synergistic "mucosal barrier disruption-pathogen translocation" model. It also highlights the potential role of host-directed adjunctive therapy in managing bloodstream infections not associated with prosthetic material.