A case report of native vertebral osteomyelitis caused by Cutibacterium modestum

Background Cutibacterium modestum was named in 2020. C. modestum was previously called Propionibacterium humerusii . Several implant-associated infections caused by Cutibacterium species have been previously reported, but native vertebral osteomyelitis due to these bacteria has rarely been reported. Case presentation A 72-year-old man, who had previously received several nerve block injections for low back pain, was referred to our hospital for deterioration in back pain in the last 1 month. MRI findings were suggestive of L5-S1 vertebral osteomyelitis. Blood cultures and bone biopsy culture revealed the presence of Gram-positive bacilli. The isolate was identified as C. modestum by 16SrRNA gene sequencing. A diagnosis of vertebral osteomyelitis caused by C. modestum was made. Minocycline followed by oral amoxicillin was administered for 3 months. His symptom improved and did not recur after treatment completion. Conclusion A case of vertebral osteomyelitis caused by C. modestum was encountered. Although C. modestum is very similar to C. acnes , it could be accurately identified by 16SrRNA gene sequencing. This case represents the first documented C. modestum infection in humans.