Different phylotypes of Cutibacterium acnes cause different modic changes in intervertebral disc degeneration

The contribution of Cutibacterium acnes (C. acnes) infection to intervertebral disc degeneration (IDD) and the antibiotic therapy has evoked several controversies in recent years. While some microbiology studies report bacterial disc infection within IDD patients, others attribute the positive results to contamination during prolonged cultures. In addition to the clinical controversy, little was known about the mechanism of C. acnes-caused Modic changes (MCs) if C. acnes was the pathogenic factor.

This study aimed to investigate the inflammatory mechanism of MCs induced by different phylotypes of C. acnes in patients with IDD.

Specimens from sixty patients undergoing microdiscectomy for disc herniation were included, C. acnes were identified by anaerobic culture, followed by biochemical and PCR-based methods. The identified species of C. acnes were respectively inoculated into the intervertebral discs of rabbits. MRI and histological change were observed. Additionally, we detected MMP expression in the rabbit model using reverse transcription-quantitative polymerase chain reaction (RT-qPCR).

Of the 60 cases, 18 (30%) specimens were positive for C. acnes, and we identified 4 of 6 defined phylogroups: IA, IB, II and III. The rabbits that received Type IB or II strains of C. acnes showed significantly decreased T1WI and higher T2WI at eighth weeks, while strain III C. acnes resulted in hypointense signals on both T1WI and T2WI. Histological examination results showed that all of the three types of C. acnes could cause disc degeneration and endplates rupture. Moreover, endplate degeneration induced by type IB or II strains of C. acnes is related with MMP13 expression. Meanwhile, strain III C. acnes might upregulated the level of MMP3.

This study suggested that C. acnes is widespread in herniated disc tissues. Different types of C. acnes could induce different MCs by increasing MMP expression.