Introduction:

Microbial etiology has been recently postulated as a cause of degenerative disc disease (DDD) leading to randomized trials of probiotics and antibiotics to treat chronic LBP. Recently the presence of disc microbiome in both healthy and diseased discs has been established by next-generation sequencing. However, the origin of disc microbiome has not been investigated. This study aims to trace the origin of human IVD microbiome.

Methods:

Lumbar discs from brain dead organ donor volunteers and patients undergoing microdiscectomy/spinal fusion were procured for this study. Normal discs (ND) group had 26 NP (Nucleus Pulposus) tissues and 17 EP (Cartilaginous Endplates) tissues excised from 10 MRI normal asymptomatic organ donor volunteers. Amplicon-sequencing was done to explore the microbial population in endplate (EP) tissues of human intervertebral disc (IVD) using NGS sequencing platform. A comparative analysis of the NP microbiome with that of EP microbiome was performed.

Results:

In total, four dominant phyla were detected in our samples: Proteobacteria, Firmicutes, Actinobacteriota and Bacteroidetes. Proteobacteria was identified as the dominant phyla in both NP and EP disc with 72% and 68% mean relative abundance respectively. Overall NP and EP had similar microbiome. A marginally higher relative abundance of Actinobacteria in NP and minor difference in relative abundance of Firmicutes were the only differences found between EP and NP. The predominant bacterial genus was again Pseudomonas in both EP and NP. However, the second predominant genus was Anoxybacillus in EP in contrast to Brevundimonas  in NP. Higher abundance of bacteria in EP compared to NP measured by beta diversity was noted.

Conclusion:

Our study explores the route of microbial entry into intervertebral disc. We found that the microbiome of nucleus pulposus and end plates are similar suggesting that the endplate could be gateway for establishment of disc microbiome.