Prevalence of Propionibacterium acnes in Intervertebral Discs of Patients Undergoing Lumbar Microdiscectomy: A Prospective Cross-Sectional Study

Abstract

BackgroundThe relationship between intervertebral disc degeneration and chronic infection by Propionibacterium acnes is controversial with contradictory evidence available in the literature. Previous studies investigating these relationships were under-powered and fraught with methodical differences; moreover, they have not taken into consideration P. acnes’ ability to form biofilms or attempted to quantitate the bioburden with regard to determining bacterial counts/genome equivalents as criteria to differentiate true infection from contamination. The aim of this prospective cross-sectional study was to determine the prevalence of P. acnes in patients undergoing lumbar disc microdiscectomy.Methods and FindingsThe sample consisted of 290 adult patients undergoing lumbar microdiscectomy for symptomatic lumbar disc herniation. An intraoperative biopsy and pre-operative clinical data were taken in all cases. One biopsy fragment was homogenized and used for quantitative anaerobic culture and a second was frozen and used for real-time PCR-based quantification of P. acnes genomes. P. acnes was identified in 115 cases (40%), coagulase-negative staphylococci in 31 cases (11%) and alpha-hemolytic streptococci in 8 cases (3%). P. acnes counts ranged from 100 to 9000 CFU/ml with a median of 400 CFU/ml. The prevalence of intervertebral discs with abundant P. acnes (≥ 1x103 CFU/ml) was 11% (39 cases). There was significant correlation between the bacterial counts obtained by culture and the number of P. acnes genomes detected by real-time PCR (r = 0.4363, p<0.0001).ConclusionsIn a large series of patients, the prevalence of discs with abundant P. acnes was 11%. We believe, disc tissue homogenization releases P. acnes from the biofilm so that they can then potentially be cultured, reducing the rate of false-negative cultures. Further, quantification study revealing significant bioburden based on both culture and real-time PCR minimize the likelihood that observed findings are due to contamination and supports the hypothesis P. acnes acts as a pathogen in these cases of degenerative disc disease.

Lumbar Disc Herniation

“…Nearly 84% of these patients were found to have P. acnes [25]. Recently, a significant portion of herniated discs (11%) have been shown to have a high P. acnes bacterial load (> 1000 CFU/mL) [26]. Aghazadeh et al also found a high prevalence of P. acnes DNA and correlated it to vertebral edema as seen on preoperative MRI [27].…”

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

“…In 11 independent studies published between 2001 and 2016, involving 1188 combined patients undergoing discectomy or microdiscectomy, this Gram-positive bacterial species was isolated from ~25% of resected disc specimens [1–11]. However, these studies had significant methodical differences and the majority was statistically underpowered [1–9] Moreover, the use of qualitative microbiologic techniques—i.e.…”

“…acnes can be slow to grow and often proliferates in vivo as aggregated biofilms, which can be challenging to cultivate in vitro and require physical biofilm disassembly (e.g. through sonication or homogenization) prior to microbiologic plating [11–13]. As a result, standard specimen preparation and culture techniques could lead to false negative results.…”

“…Based on these methodological issues, it is not surprising that the prevalence rate of cultured P . acnes in previous publications ranges from 0 to 44% [11]. …”

Histological Identification ofPropionibacterium acnesin Nonpyogenic Degenerated Intervertebral Discs

“…Previous studies have demonstrated that the prevalence of low-virulence anaerobic bacterium ranged from 20% to 53% [1–7]. Among them, P. acnes has been found to account for as much as 84% of all isolated bacteria [7].…”