OP2 -Identification of Anaerobic Bacteria in Herniated Lumbar Discs of Patients Undergoing Microdiscectomy

Abstract

Introduction

Although studies have indicated that vertebral discs are sterile, emerging evidence suggests the presence of low-virulent anaerobes in herniated discs. This finding indicates that the presence of anaerobes could be attributed to the disease's pathophysiology and post-surgical effects in lumbar disc herniation (LDH), apart from traditional causative factors.

 Objective

This study aimed to identify the presence of anaerobes in herniated lumbar discs in patients undergoing lumbar microdiscectomy.

 Design, setting, and methods

A cross-sectional study was conducted from 2022 to 2024 in patients with LDH (n=101) undergoing lumbar microdiscectomy at selected hospitals in Sri Lanka. Anaerobic bacterial cultures were performed on all surgically excised discs and transported separately in both enrichment media [Robertson cooked meat media (RCM) and thioglycolate (TG) broth]. To rule out bacterial contamination, skin scrapings and muscle biopsies were collected as controls and processed concurrently with the disc cultures. Discs collected within RCM were directly sub-cultured. TG specimens were homogenized using a Seward 400 Stomacher machine and subsequently inoculated onto brucella blood agar and bacteroides bile esculin agar. The cultures were incubated under an anaerobic glove box, and culture negatives were confirmed after 14 days of incubation. Isolates were screened by colony morphology, Gram stain, and aerotolerance and then confirmed with the Rapid ID 32A kit.

Results

Of the total LDH cases (29/101), 28.71% yielded positive results for anaerobic culture, with 19/29 cultures testing positive in RCM and 14 in TG media, while four discs showed bacterial growth in both media. The study identified a diverse range of anaerobic bacterial isolates, including Actinomyces meyeri (7/29) 24.14%, Parvimonas micra (6/29) 20.69%, Gemella morbillorum (5/29) 17.24%, Capnocytophaga sputigena (4/29) 13.79%, Parabacteroides distasonis, Propionibacterium propionicum (2/29 each) 6.9%, Actinomyces naeslundii, Propionibacterium acnes and Veillonella spp. (1/29 each) 3.45%. None of the controls generated any anaerobic bacterial growth throughout the study.

 Conclusions

This study revealed diverse anaerobes in excised herniated lumbar discs, with Actinomyces meyeri as the predominant isolate, followed by other facultative and obligate anaerobes. Higher culture positivity in RCM than in TG indicates media-specific differences in anaerobe yield. The presence of anaerobes may implicate their role in LDH pathophysiology.

Acknowledgment: Grant No: ASP/01/RE/AHS/2021/87.