Background: Low back pain (LBP) with or without lumbar disc herniation (LDH) is one of the most commonly found symptoms worldwide. The etiology is often unclear, but a low-grade infection caused by the anaerobic skin bacterium Cutibacterium acnes (formerly Propionibacterium acnes), sometimes found on culture during LDH surgery, has been suggested as a cause. Given worldwide concern over multidrug resistant bacteria, further investigation is highly warranted. Our study aimed to compare findings regarding bacterial presence in painful lumbar degenerative disc disease (DDD) in adults having LDH with findings in young patients with scoliosis, but without DDD or relevant lumbar pain. Methods: Between 2015 and 2017, 40 adults with LDH (median age 43, IQR 33-49) and 20 patients with scoliosis (median age 17, IQR 15-20) underwent surgery at seven Swedish hospitals. Samples were collected and cultured from skin, surgical wound, discs and vertebrae. Genetic relatedness of C. acnes isolates was investigated using single nucleotide polymorphism (SNP) analysis. DNA samples collected from discs/vertebrae were analysed using 16S rRNA-based PCR sequencing. Preoperative MRI findings were assessed for inflammatory Modic changes. Findings: No bacterial growth was found in 6/40 (15%) LDH patients, compared with 3/20 (15%) scoliosis patients. A single species, C. acnes, was found exclusively in the disc/vertebra from one patient in each group; in the LDH group, 29/40 (72%) patients had at least one sample with growth of C. acnes, while the corresponding figure in the scoliosis group was 14/20 (70%). There was no association between bacterial findings and Modic changes. Interpretations: The results suggest that finding bacteria like C. acnes in discs and vertebrae during surgery is likely due to contamination. Antibiotic use to treat LBP/LDH without signs of clinical discitis/spondylitis should be seriously questioned. Funding Statement: The study was funded by FORSS, a Swedish regional research foundation Declaration of Interests: The authors state: " no conflicts of interest to declare."Ethics Approval Statement: The study was approved by the ethical committee in Linköping (EPN, Ref. no. 2015/152-31). All patients gave their written informed consent.

Purpose To compare bacterial findings in pain-generating degenerated discs in adults operated on for lumbar disc herniation (LDH), and mostly also suffering from low back pain (LBP), with findings in adolescent patients with non-degenerated non-pain-generating discs operated on for scoliosis, and to evaluate associations with Modic signs on magnetic resonance imaging (MRI). Cutibacterium acnes ( Propionibacterium acnes ) has been found in painful degenerated discs, why it has been suggested treating patients with LDH/LBP with antibiotics. As multidrug-resistant bacteria are a worldwide concern, new indications for using antibiotics should be based on solid scientific evidence. Methods Between 2015 and 2017, 40 adults with LDH/LBP (median age 43, IQR 33–49) and 20 control patients with scoliosis (median age 17, IQR 15–20) underwent surgery at seven Swedish hospitals. Samples were cultured from skin, surgical wound, discs and vertebrae. Genetic relatedness of C. acnes isolates was investigated using single-nucleotide polymorphism analysis. DNA samples collected from discs/vertebrae were analysed using 16S rRNA-based PCR sequencing. MRI findings were assessed for Modic changes. Results No bacterial growth was found in 6/40 (15%) LDH patients, compared with 3/20 (15%) scoliosis patients. Most positive samples in both groups were isolated from the skin and then from subcutis or deep within the wound. Of the four disc and vertebral samples from each of the 60 patients, 235/240 (98%) were DNA negative by bacterial PCR. A single species, C. acnes , was found exclusively in the disc/vertebra from one patient in each group. In the LDH group, 29/40 (72%) patients had at least one sample with growth of C. acnes, compared to 14/20 (70%) in the scoliosis group. Bacterial findings and Modic changes were not associated. Conclusions Cutibacterium acnes found in discs and vertebrae during surgery for disc herniation in adults with degenerated discs may be caused by contamination, as findings in this group were similar to findings in a control group of young patients with scoliosis and non-degenerated discs. Furthermore, such findings were almost always combined with bacterial findings on the skin and/or in the wound. There was no association between preoperative Modic changes and bacterial findings. Antibiotic treatment of lumbar disc herniation with sciatica and/or low back pain, without signs of clinical discitis/spondylitis, should be seriously questioned. Graphic abstract These slides can be retrieved under Electronic Supplementary Material.