Deep Spinal Infection Caused by

Corynebacterium simulans is a commensal coryneform bacterium that commonly colonizes human skin and mucosal surfaces. Owing to limitations in conventional microbiological identification, it is often regarded as a contaminant, and clinically significant deep-seated infections caused by this organism are rarely reported. Here, we describe a case of lumbar infectious spondylitis caused by C. simulans in a 62-year-old male farmer who presented with a 2-month history of persistent low back pain accompanied by pain in both lower limbs. The patient had several potential predisposing factors including repeated unregulated needle-pricking bloodletting therapy, previously unrecognized hyperglycemia, and a family history of psoriasis. Lumbar magnetic resonance imaging and computed tomography revealed destructive infectious lesions involving the L3 and L4 vertebral bodies and L3/4 intervertebral disc. Blood culture initially yielded coryneform bacilli from a single anaerobic bottle, whereas repeated blood cultures were subsequently negative, supporting the possibility of contamination. However, given the compatible clinical manifestations, elevated inflammatory markers, and imaging evidence of spinal infection, percutaneous vertebral biopsy was performed. Routine bacterial culture of the deep-tissue specimen showed no growth, whereas metagenomic next-generation sequencing identified C. simulans with high sequence reads and relative abundance, supporting its etiological relevance in the appropriate clinical context. The patient was treated with intravenous vancomycin combined with glycemic control, followed by oral linezolid as step-down therapy. His symptoms gradually improved, inflammatory markers decreased toward the normal range, and follow-up magnetic resonance imaging showed reduced paravertebral soft tissue edema. No recurrence was observed during the 3-month follow-up period. This case highlights that Corynebacterium species detected in the blood or deep tissue specimens should not be readily dismissed as contaminants in patients with compatible evidence of infection. Deep tissue sampling combined with metagenomic next-generation sequencing (mNGS) may improve the detection of rare opportunistic pathogens and facilitate timely targeted antimicrobial therapy.