Is the Intervertebral Disc Really Sterile?

What the “Gut–Disc Axis” Is Teaching Us About Back Pain-

by Bill Frank, DC- Associate Professor Department of Neurobiology and Anatomy; Drexel University College of Medicine, West Reading Campus

Not long ago, I stood in front of a classroom teaching something I had said countless times before: “The nucleus pulposus—the center of the intervertebral disc—is sterile.” It’s one of those concepts we rarely question. The disc is relatively avascular. It’s enclosed. It’s protected. It exists, in many ways, in isolation.

And for years, that made perfect sense. But recently, I came across a paper that made me pause—and rethink that assumption entirely. A 2026 review titled “The Gut–Disc Axis: Unraveling the Microbiome’s Role in Lumbar Disc Herniation” brings together a growing body of research suggesting that both the gut microbiome and even local bacteria within the disc may influence disc health and pain (Ambrosio et al., 2026).

And once you read it, a simple question becomes unavoidable: “ If the disc is supposed to be sterile… why are bacteria being found inside it?”

From Isolation to Connection

As someone who teaches nutrition and gut health, I spend a lot of time talking about the microbiome—especially the gut microbiome—and its role in inflammation, immunity, and chronic disease. We’ve learned that the gut influences:

• metabolic health
• immune responses
• systemic inflammation

But now, research is expanding that conversation. There’s growing interest in what’s being called the gut–disc axis—a concept suggesting that the microbiome may influence spinal health both systemically and locally (Ambrosio et al., 2026; Li et al., 2024; Zhang et al., 2025). At the same time, studies of herniated discs are detecting bacteria where we never expected to find them (Capoor et al., 2017; Dudli et al., 2018). This doesn’t mean we abandon what we know. But it does mean we may need to expand the model.

The Unexpected Guest: Cutibacterium acnes

Cutibacterium acnes is not a rare organism. It lives quietly on our skin and is best known for its role in acne. But biologically, it has some important characteristics:

• It thrives in low-oxygen environments
• It can trigger chronic, low-grade local inflammation
• It forms biofilms – often associate with artificial joint prosthesis and iatrogenic infections (post-surgical)

And importantly – it has been detected in surgically excised disc material in multiple studies (Capoor et al., 2017; Dudli et al., 2018). Some research has also linked bacterial presence to Modic changes – inflammatory changes in adjacent vertebrae associated with chronic low back pain (Albert et al., 2013). The Neurospine review highlights these findings while also emphasizing a critical point: Results across studies are inconsistent, and contamination remains a concern (Ambrosio et al., 2026).

How Would Bacteria Get Into the Disc?

This is where the discussion becomes especially compelling – and where your original question lies at the center of the science. The review suggests that lumbar disc herniation itself may change the biology of the disc in important ways. Under normal conditions, the disc is relatively avascular, isolated, and immune-privileged (sterile). But when herniation occurs, the annulus fibrosus is disrupted, the nucleus pulposus material is exposed, and immune and vascular responses are activated.

At that point, the disc is no longer isolated. It becomes, as described in the paper –

exposed to systemic bodily systems and their respective microbiomes (Ambrosio et al., 2026). This creates a window where bacteria could potentially access disc tissue through hematogenous spread (via bloodstream), neovascularization after injury, or possibly be introduced during surgical handling. Each of these remains under investigation.

Two Interacting Systems: Systemic and Local

One of the most important contributions of this paper is the idea that we are not dealing with a single mechanism—but with interacting biological systems.

1. Systemic Influence: The Gut–Disc Axis

The gut microbiome plays a central role in regulating inflammation, immune signaling, and metabolic activity. Disruptions in the gut microbiome (dysbiosis) can increase pro-inflammatory cytokines, immune dysregulation, and systemic inflammatory burden. These changes have been linked to disc degeneration and pain (Ambrosio et al., 2026; Li et al., 2024; Tilg et al., 2020). Emerging work also suggests a causal relationship between gut microbiota composition and intervertebral disc degeneration (Zhang et al., 2025).

2. Local Influence: A Possible Disc Microenvironment

At the same time, there is growing evidence that bacteria may exist within the disc itself. These microbes may influence extracellular matrix breakdown, contribute to inflammation, and even affect pain pathways. However, as emphasized in multiple studies, it is still unclear whether this represents true colonization or contamination (Ambrosio et al., 2026; Capoor et al., 2017).

Rethinking Back Pain

For decades, we’ve viewed disc herniation as a mechanical problem. But this research suggests a more complete picture –  Mechanical + inflammatory + potentially microbial. Even if bacteria are not the primary cause, they may amplify inflammation, influence healing, and contribute to chronic pain states.

Why This Matters for Gut Health

This is where everything connects. If the gut microbiome influences systemic inflammation, immune function, and tissue health, then it is reasonable to consider that gut health may influence spine health.

Research suggests that microbiome imbalance may accelerate disc degeneration through inflammatory and immune-mediated pathways (Li et al., 2024; Zhang et al., 2025). For those of us focused on prevention, this reinforces a key principle – the body does not function in isolated compartments.

Supporting gut health may support inflammatory balance, tissue resilience, and recovery processes. Examples of nutritional choices include:

• whole, fiber-rich nutrition
• reducing ultra-processed foods
• supporting microbial diversity
• maintaining metabolic health

A Necessary Note of Caution

This is an evolving area of research. Not all studies agree. Detection methods vary. And causation has not been established. Even the Neurospine review emphasizes the need for standardized methods and further investigation (Ambrosio et al., 2026)

Final Thoughts

For years, we’ve been taught that the intervertebral disc is sterile. That concept shaped how we understand spine health. But science evolves. And what this emerging body of research suggests is not that we were wrong…but that we may have been incomplete.

The disc may not be as isolated as we once believed. And the microbiome – especially the gut microbiome – may play a role in spinal health that we are only beginning to understand.

For those of us focused on prevention, this reinforces a powerful message: supporting gut health is not just about digestion, it may be about supporting the entire musculoskeletal system.

In a previous post, I revisited Hippocrates’ famous statement that “all disease begins in the gut.” While we now understand that statement is not absolute, modern research continues to validate its underlying principle—that the gut plays a central role in systemic health.

Perhaps this emerging research on the gut–disc axis is another example of that principle in action. And for clinicians, it offers an important reminder – when evaluating patients with persistent or recurrent back pain, it may be worth asking not only what is happening in the spine—but what is happening in the gut.

References

• Ambrosio L, Schol J, Sima S, et al. The Gut–Disc Axis: Unraveling the Microbiome’s Role in Lumbar Disc Herniation. Neurospine. 2026. doi:10.14245/ns.2551584.792
• Albert HB, Lambert P, Rollason J, et al. Does nuclear tissue infected with bacteria following disc herniations lead to Modic changes (“Vertebral Endplate Changes / Modic Changes: An Audit Study Using …”) Eur Spine J. 2013.
• Capoor MN, Ruzicka F, Schmitz JE, et al. Propionibacterium acnes in intervertebral disc tissue. Spine. 2017.
• “Dudli S, Fields AJ, Samartzis D, et al. Pathobiology of Modic changes. (“Inflammatory Response of Disc Cells Against Propionibacterium acnes …”) Eur Spine J. 2018.
• Li W, et al. The gut–disc axis and intervertebral disc degeneration. Front Cell Infect Microbiol. 2024.
• Zhang T, et al. Gut microbiota and intervertebral disc degeneration: causal insights. Eur Spine J. 2025.
• Tilg H, Zmora N, Adolph TE, Elinav E. The intestinal microbiota in health and disease. Nat Rev Immunol. 2020.
• O’Connell RM, et al. Microbiome influences on musculoskeletal health. Nat Rev Rheumatol. 2025.