INTRODUCTION
Lower back pain is the leading cause of disability worldwide and is often associated with age-related intervertebral disc degeneration in humans. Vertebral endplate damage may precede disc degeneration, triggering inflammation and Modic change. Modic change (MC) are pathological alteration to vertebral bone marrow, visible on MR scan. Modic type 1, 2 and 3 are recognised with type 1 (MC1) being the most inflammatory. Previous microbiological studies have cultured bacteria, particularly Cutibacterium acnes, from inververtebral discs excised in patients with Modic change. It is hypothesized that endplate damage creates a "leaky" environment, allowing microbes to enter and potentially provoking an inflammatory reaction (MC1). The aim of the study was to determine whether human degenerative discs with adjacent MC1 demonstrate occult infection compared to discs without MC1.
METHODS
In this study, 118 patients undergoing first episode of lumbar disc surgery were recruited. Prior to surgery routine clinical data and questionnaires were collected on diet, medication, and antibiotic exposure. All patients underwent spine MR scanning as part of routine clinical care and the 3 types of MC defined by consultant radiologists. Stools were collected pre-operatively, and measured with metagenomics sequencing. During surgery disc and endplate material were collected, and skin swabs was obtained from patients and operating theatre staff for microbial DNA sequencing. Targeted full-length16S rRNA sequencing by PacBio was used to determine the composition of any bacteria. The sequences were then QCed, trimmed and annotated with DADA2 pipeline and SILVA database.
RESULTS
The most abundant bacteria detected in spine disc was Cutibacterium acnes, present in 97 out of 110 disc samples, confirming its presence in degenerative discs. Differential abundance tests revealed that in discs with adjacent MC1 (n = 29) compared to the discs without any adjacent MC (n = 44), the abundance of Staphylococcus epidermidis is significantly higher (adjusted p < 0.05) when adjusted for age, sex, and BMI. In discs with any type of MC in the adjacent endplate and vertebra (n= 55) compared to those without any MC (n= 44), the abundance of Aureimonas A sp001425485 was significantly higher while another species, Pseudomonas yamanorum had lower abundance (adjusted p < 0.05).
In our initial results 393 taxa were identified from spine and skin samples. There was a significant difference of the microbial composition between spine and skin samples (p = 0.001) by PERMANOVA test suggesting the detected microbes in spine discs are unlikely due to contamination from skin and environment during sample collection.
DISCUSSION
This work confirmed the presence of bacteria in the degenerate discs using culture-free methods based on DNA. Further analysis will be done by sequencing more skin swabs from patients and operating staff to rule out the cross-contamination and define the source of the bacteria in the spine samples if possible.