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Herniated or Slipped Disk and the Possible Role of Bacteria

Linda Crampton is a writer and former teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

Illustration of a vertebra with a herniated disk and an MRI (magnetic resonance imaging) picture of a real herniation

Illustration of a vertebra with a herniated disk and an MRI (magnetic resonance imaging) picture of a real herniation

Herniated Disks and Bacteria

A herniated or slipped disk in the spine is often a painful condition. The outer part of the disk ruptures, and the inner part protrudes and presses on a nerve. Physical therapy and anti-inflammatory medicines frequently reduce the pain and help the body to heal itself. Unfortunately, sometimes the pain persists and the problem becomes chronic. In this situation, spinal surgery may be recommended.

Researchers from the University of Southern Denmark have found bacterial infections in some herniated disks. They believe that 20% to 40% of chronic back pain cases associated with a herniation are produced by a bacterial infection. The scientists also say that antibiotics (or at least the one that they tested) can reduce the pain.

Some investigators are intrigued by the possibility of a link between bacteria and back pain caused by a herniated disk. Other investigators besides the Danish ones have found bacteria in damaged disks. Some scientists haven't found bacteria in the disks, however, and they suspect that there have been procedural errors in some experiments. More research is necessary to clarify the situation.

Seven cervical vertebrae are found in the neck, twelve thoracic ones in the upper back, five lumbar ones in the lower back, five fused ones in the sacrum, and three to five fused ones in the coccyx. According to the Mayo Clinic, most herniated disks occur in the lower back, but some occur in the neck.

Two vertebrae and an intervertebral disk

Two vertebrae and an intervertebral disk

A Spinal or Intervertebral Disk (or Disc)

Some people refer to rules stating when "disk" and "disc" should be used, but these rules aren't universally followed. I refer to a spinal "disk" like MedlinePlus (a National Institutes of Health site) and the Mayo Clinic often do, but the spelling is really a matter of personal preference.

Disks are short, cartilaginous cylinders that are located between the vertebrae, or bones, of the spine. They lie on top of the body of a vertebra. The disks absorb shock created by movements such as running and jumping and also prevent the vertebrae from grinding against each other and breaking down.

The parts of a spinal disk are listed and described below. They are shown in the illustration above and in the first image in this article.

  • The annulus fibrosis is the tough and fibrous outer surface of the disk.
  • The nucleus pulposus is the gelatinous inner portion of the disk.
  • The nucleus pulposus is made of loosely arranged fibers in a gel made of molecules called mucoprotein.
  • Mucoproteins consist of both protein and a type of carbohydrate called a glycosaminoglycan. Glycosaminoglycans make liquids viscous.

What Is a Herniated Disk?

Back pain may be due to arthritis or a problem with back muscles, ligaments (which attach bones to one another), or tendons (which attach muscles to bones). A doctor's diagnosis is needed to identify the cause of back pain and to confirm that a back problem is actually due to a herniated disk.

Herniated disks are also known as slipped, ruptured, or prolapsed disks. A slipped disk hasn't moved out of place, despite its name. Instead, the outer layer of the disk has ruptured, allowing the softer inner tissue to bulge outwards. A prolapse is a condition in which an entire organ moves out of place. The term "herniated disk" is probably the best one in reference to the spine because it's the most accurate. A hernia is a condition in which part of an organ protrudes through the structure that encloses it.

The body attempts to heal the broken surface of a disk and remove the expelled material. Before the area is repaired, however, the person may be in pain. The pain arises due to the inner tissue of the disk pressing on a spinal nerve and irritating it.

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A herniated disk in a lumbar vertebra as viewed from the side

A herniated disk in a lumbar vertebra as viewed from the side

Herniated disks are most common in middle-aged people. Being overweight increases the risk of a disk rupture. A sudden strain or repetitive activities may be the immediate cause of the injury, however.

Possible Symptoms of the Disorder

Some people have no symptoms from a herniated disk. The rupture may be small or may not affect a nerve. In other people, there may be pain for a while, but the pain may disappear as the body repairs the rupture and breaks down the material that was released from the disk. The healing process may take weeks or even months. Unfortunately, some people experience chronic pain from a herniated disk.

The nerve irritation caused by the hernia can produce pain, numbness, and tingling. There may also be weakness in the muscles controlled by the affected nerves. If a disk in the neck is herniated, the pain often appears in a shoulder and arm. If the damaged disk is in the lower back, the person frequently feels pain in their buttocks, thigh, and leg. Sometimes pain will appear in the foot as well.

If the pressure on a nerve in the lower back is intense, the person may lose control of urination or defecation. These conditions are medical emergencies and require immediate attention. Coughing, sneezing, laughing, urinating, and defecating can all increase the pain from a herniated disk.

Bacteria and Chronic Back Pain

The results of the Danish experiment seem to have intrigued many researchers. Some scientists have concerns about the discoveries, however. They say that despite the careful techniques used in the Danish experiment, bacteria may have appeared in their disk samples due to contamination. This possibility shouldn't be discounted. The idea that bacteria are present in herniated disks is very interesting, though.

The research done so far suggests that in order for an intervertebral disk to be infected by bacteria (if this actually happens), it must first rupture. The rupture causes the initial pain when the contents of the disk affect a nerve. The Danish researchers say that as the body heals the injury, blood vessels extend into the disk. Bacteria in the blood can therefore enter the disk, where they multiply and cause an infection. Inflammation, swelling, and tiny fissures have been observed in the bones of the vertebrae around herniated disks. The investigators believe that bacterial infections cause these conditions.

One treatment for a herniated disk that's causing continuous problems is to surgically remove the displaced tissue. The Danish researchers examined the spinal tissue taken from people who had undergone surgery for chronic back pain. They followed "stringent antiseptic sterile protocols" to avoid contamination of the samples with bacteria from another source. The researchers found that nearly half of the samples were infected by bacteria. In addition, they discovered that more than eighty percent of the infected samples contained a bacterium called Propionibacterium acnes—the same bacterium that is involved in acne. The bacterium is sometimes known as Cutibacterium acnes.

Propionibacterium acnes normally lives on our skin, in our mouths, and in our large intestine. It can also enter our blood. The researchers think that the bacterium travels to damaged spinal disks in the bloodstream and then releases chemicals that trigger inflammation.

Testing the Use of Antibiotics for Pain Relief

In another experiment, the Danish researchers gave antibiotics to people who had suffered from back pain for at least six months and had evidence of spinal disk damage and vertebral swelling around the damage. (The subjects weren't tested for the presence of bacteria in their spine.) Other people with these same conditions were given a placebo.

Antibiotic treatment for 100 days reduced pain and other problematic conditions significantly in people given an antibiotic compared to those given a placebo. The increased benefits were still present and in some cases had even improved one year after the initial evaluation.

It's important to note that the people in the test had specific problems in their spine. Antibiotics haven't yet been tested on other people with back pain. In addition, since the overuse of antibiotics has led to frightening resistance to the medications in bacteria, it's vital that antibiotics aren't prescribed for back pain patients "just in case" they help them.

It’s thought that some categories of antibiotics can reduce inflammation in addition to reducing infection. Reducing inflammation when no bacteria were present may have reduced pain in the Danish experiment.

Certain antibiotics might help some types of chronic back pain. They mustn't be taken unnecessarily, however.

Certain antibiotics might help some types of chronic back pain. They mustn't be taken unnecessarily, however.

Possible Problems in the Research

Research involving humans is often difficult because so many factors are involved. For example, bacteria are tiny and ubiquitous creatures and often appear where they're not wanted. Very careful procedures are needed to prevent contamination of a tissue sample when the sample is extracted or examined.

Good experiments use a placebo. A placebo is a harmless substance that has no medical benefit when administered to a patient. Some subjects in an experiment are given a placebo and some are given the test treatment. The subjects don't know which type of treatment they are receiving. This procedure enables the researchers to take the "placebo effect" into account when analyzing the results of the experiment. Sometimes knowing that something may help us enables us to feel better, even when the treatment has no known benefit.

All experiments involving humans need to be double blind. A double blind experiment is one in which neither the subjects nor the person administering a treatment know its identity. Unfortunately, the Danish antibiotic experiment may not have been completely double blind. Some of the subjects that were given antibiotics may have suspected that they had received a medication because they experienced diarrhea as a side effect of the treatment. This suspicion may have affected the outcome of the experiment.

Surveys of Scientific Literature

2015 Research

The Danish research was reported in 2013. Since that time, other researchers have found bacteria in herniated disk material. In 2015, a group of Australian doctors and researchers analyzed the scientific literature with respect to the possible link between bacteria in herniated disks and chronic pain. They found that bacteria are commonly detected in herniated disks. They say that at the moment there is "modest" evidence supporting the idea that the bacteria contribute to a patient's pain. They also say that further research is needed to demonstrate that the bacteria that have been discovered are not the result of tissue contamination.

2019 Research

A 2019 study published in the European Spine Journal also explored the relevant scientific literature. The investigators noticed the heterogeneity (different conditions) used in the studies. Tissue is taken from a patient's injured disk during surgery and then cultured to see if bacteria are present. One problem that the investigators observed was the variation in sampling techniques. Another was that different culture conditions were used in different experiments. Some of the conditions may not have supported the survival or growth of Propionibacterium acnes.

Despite the problems mentioned above, the investigators noted that bacteria were found in a significant number of disk samples. They concluded that bacteria might cause disk pain, but this is uncertain due to the heterogeneity of the experimental conditions.

2020 Research

In 2020, a research team published their results obtained from living but brain-dead patients. Instead of looking for bacterial cells in the disks of the patients, they looked for RNA (ribonucleic acid) made by the bacteria. Since the patients were legally dead, the scientists were able to extract a lot of material from the disks. They found evidence of a bacterial community inside the disks. They also found that the community in healthy disks was different from that in degenerated or herniated ones. The results of the research were published in the European Spine Journal.

A side and back view of three vertebrae that shows the intervertebral disks

A side and back view of three vertebrae that shows the intervertebral disks

A Controversial Topic

While the results of the Danish investigations are interesting and have impressed many people, they don't prove that bacteria contribute to the pain of herniated disks. The source of the bacteria and the effects of different types of antibiotics need to be clarified. Even if bacteria are present in damaged disks, it doesn't necessarily mean that they are responsible for the patient's pain.

Some scientists believe that it's highly likely that bacteria found in tissue from herniated disks are present due to contamination of the samples during the testing process. Some researchers have looked for bacteria in damaged disks and found none, and some have found that at least some antibiotics don't help patients' pain. Other researchers are not so certain that the presence of bacteria in herniated disk tissue is due to contamination and believe that more studies under specific conditions are necessary. The 2020 research in particular is interesting.