Propionibacterium acnes biofilm is present in intervertebral discs of patients undergoing microdiscectomy

Abstract

BackgroundIn previous studies, Propionibacterium acnes was cultured from intervertebral disc tissue of ~25% of patients undergoing microdiscectomy, suggesting a possible link between chronic bacterial infection and disc degeneration. However, given the prominence of P. acnes as a skin commensal, such analyses often struggled to exclude the alternate possibility that these organisms represent perioperative microbiologic contamination. This investigation seeks to validate P. acnes prevalence in resected disc cultures, while providing microscopic evidence of P. acnes biofilm in the intervertebral discs.MethodsSpecimens from 368 patients undergoing microdiscectomy for disc herniation were divided into several fragments, one being homogenized, subjected to quantitative anaerobic culture, and assessed for bacterial growth, and a second fragment frozen for additional analyses. Colonies were identified by MALDI-TOF mass spectrometry and P. acnes phylotyping was conducted by multiplex PCR. For a sub-set of specimens, bacteria localization within the disc was assessed by microscopy using confocal laser scanning and FISH.ResultsBacteria were cultured from 162 discs (44%), including 119 cases (32.3%) with P. acnes. In 89 cases, P. acnes was cultured exclusively; in 30 cases, it was isolated in combination with other bacteria (primarily coagulase-negative Staphylococcus spp.) Among positive specimens, the median P. acnes bacterial burden was 350 CFU/g (12 - ~20,000 CFU/g). Thirty-eight P. acnes isolates were subjected to molecular sub-typing, identifying 4 of 6 defined phylogroups: IA1, IB, IC, and II. Eight culture-positive specimens were evaluated by fluorescence microscopy and revealed P. acnes in situ. Notably, these bacteria demonstrated a biofilm distribution within the disc matrix. P. acnes bacteria were more prevalent in males than females (39% vs. 23%, p = 0.0013).ConclusionsThis study confirms that P. acnes is prevalent in herniated disc tissue. Moreover, it provides the first visual evidence of P. acnes biofilms within such specimens, consistent with infection rather than microbiologic contamination.

Bacterial biofilms: a possible mechanism for chronic infection in patients with lumbar disc herniation – a prospective proof‐of‐concept study using fluorescence in situ hybridization

“…Microscopy revealed inflammatory cells spread throughout the tissue and in close proximity to the aggregates. Morphology of bacterial aggregates resembled those observed in a previous study of infected ligament reconstructions , but differed from those previously observed in LDH tissue . We hypothesize that the presence of an EPS matrix may obscure the morphology of individual cells as other studies also demonstrate difficulty in resolving single bacterial cells from FISH staining in several types chronic infections .…”

The bacteria-positive proportion in the disc tissue samples from surgery: a systematic review and meta-analysis

“…Although the culture result is controversial, many other methods like HE and modified Brown-Brenn staining [7], confocal scanning laser microscopy [14], fluorescence in situ hybridization [35], liquid chromatography-tandem mass spectrometry (LC-MS/MS) [36] and PCR assay [12,15,36,37] have provided the evidence for the presence of bacteria. Studies have also demonstrated the differences between genotypes of P. acnes from intervertebral discs and skin.…”

“…Every study reported more than one kind of bacteria except the studies by Javanshir [13] and Lin [9] (See supplementary Table 2). Two studies included more than 300 cases [3,14]. One study [15] had more than 200 cases, and four studies reported more than 100 cases [9,13,16,17].…”

Letter to the Editor concerning “Low virulence bacterial infections in cervical intervertebral discs: a prospective case series” by Chen Y, Wang X, Zhang X, et al. (Eur Spine J; 2018: doi:10.1007/s00586-018-5582-4)

“…Nonetheless, if an attempt is to be made to investigate the prevalence of low virulence infection, such as P. acnes, with cervical discs, then we feel the methodological and data analysis issues described here may have compromised any clear conclusions, especially as P. acnes does appear to be significantly represented within infected discs [2].…”

“…To ensure that the 95% confidence interval estimate of the proportion positive cases is within 5% of the true proportion, a sample size of approximately 350 cases is necessary. Indeed, in our previous work we looked at 368 patients to draw statistically relevant conclusions [2]. 3.…”