mNGS technique was used to analyze the microbiome structure of intervertebral disc tissue in 99 patients with degenerative disc disease.

Objective: Whether bacterial hypotoxic infection in the intervertebral disc is the cause of disc degenerative disease (DDD) is controversial. The mNGS technique can provide valuable insights by obtaining more comprehensive evidence of the presence of bacteria in the intervertebral disc. This study was designed to analyze the characteristics of intervertebral microbiome structure in patients with lumbar disc degenerative disease and its correlation with clinical indicators.

Methods: A total of 104 patients with lumbar disc degenerative diseases were included in this study. The surgically removed lumbar intervertebral disc tissues were collected for clinical culture and metagenomic second-generation sequencing (mNGS), and the consistency of the two microbial detection methods was compared.According to the collected clinical information, patients were grouped according to the modified Pfirrmann grading, Modic typing and age, and the differences of microbial communities detected by mNGS among different groups were compared, including α diversity analysis, β diversity analysis, species abundance difference analysis, etc. Spearman correlation between clinical features and generic relative abundance was calculated.

Results: The effective culture results of 104 intervertebral disc tissue samples were only 19 cases positive, with a positive rate of 18.3% (19/104), and the mNGS detection results were positive in 99 cases, with a positive rate of 95.2% (99/104). According to the 19 samples with positive culture, nearly half 47.4% (9/19) of staphylococcus species were positive, and all the positive species were basically epidermal common colonization species or environmental common bacteria. At the same time, we conducted two times of mNGS sequencing for these 19 samples, and the consistency rate between the two sequencing results and the culture results was 84.2% (16/19). According to the results of mNGS detection, 250 species from 110 genera were detected in 99 positive samples. The results of group analysis showed that patients with lower degree of disc degeneration (modified Pfirrmann ≤ 4) and young patients (age < 45 years) had more abundant microbial communities in disc tissue (P < 0.05). Correlation analysis showed that there was a positive correlation between Arcobacter skirrowii and improved Pfirrmann classification at the species level (P < 0.01). There was a negative correlation between pseudomonas thermotolerans and modified Pfirrmann classification (P < 0.05). There was a positive correlation between Staphylococcus hominis and Modic typing scores (P < 0.05). Staphylococcus arlettae was negatively correlated with age (P < 0.05). At the genus level, Arcobacter had a significant positive correlation with the modified Pfirrmann grade and Modic classification (P < 0.05), Corynebacterium had a significant negative correlation with the modified Pfirrmann grade (P < 0.05), and Pseudomonas had a significant negative correlation with age (P < 0.05). After our follow-up of six months to one year, two of the patients included in this study eventually developed severe lumbar disc infection, and the rest did not develop infection.

Conclusions: This study proves that hypotoxic infection may be involved in the degeneration of intervertebral disc, and the bacterial species that cause this occult infection may be more abundant than previously thought. In addition, there was a significant correlation between the biome structure of these bacteria and clinical indicators. The hypothesis of the cause of this insidious infection has the potential to change the way the disease is treated.