Ulcerative colitis (UC) is a type of inflammatory bowel disease (IBD). It involves chronic inflammation of the large intestine.

UC causes symptoms such as abdominal pain, urgent bowel movements, and bleeding from the rectum. Symptoms tend to get better and worse, during periods of remission and relapse.

The exact cause of UC is unknown. However, many experts believe that it results from an abnormal immune response to bacteria in the bodies of people who are genetically predisposed to develop this condition.

Below, we explore the roles that gut bacteria may play in the development and treatment of UC.

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The human digestive system is home to trillions of bacteria and other microbes. This community of microbes and the products that they produce are, collectively, called “the microbiome.”

Some bacteria in the gut can cause disease. Other bacteria are “friendly,” playing important roles in human health. For example, certain bacteria help the body digest food, produce vitamins, and regulate immune responses.

Many factors affect the types, numbers, and activities of bacteria in the gut. Mothers pass on gut bacteria to their babies, and a person’s genetics, diet, and exposure to antibiotics can also affect the composition of their gut microbiome.

When there is an irregular balance of bacteria and other microbes in the gut, this may contribute to the development of certain diseases.

“We know that the gut bacteria, or microbiome, of people with UC is different, compared to that of healthy people,” Dr. Kerri Glassner, a gastroenterology fellow at Houston Methodist Hospital, in Texas, told Medical News Today.

For example, people with IBD tend to have less diverse microbiomes, compared with healthy people. Their microbiomes also tend to be less stable, the authors of a review in the journal Nutrients report.

They typically have lower populations of friendly bacteria, such as Bifidobacterium, Lactobacillus, and Faecalibacterium prausnitzii. Meanwhile, they often have more potentially pathogenic bacteria — such as Escherichia coli.

Accordingly, people with UC tend to have lower levels of certain metabolites produced by friendly bacteria.

For instance, some bacteria break down food into short-chain fatty acids. These acids help the gut microbiome communicate with the immune system. People with active IBD have lower levels of short-chain fatty acids in their stool, according to a study in Gastroenterology.

Some of these changes may contribute to the development of UC, while others may result from the condition.

“There is some evidence to suggest that changes in gut bacteria may occur prior to the development of UC,” Dr. Glassner said.

“However, both UC itself, as well as treatments used for UC, can change the microbiome composition,” she continued. “This makes it challenging to determine how much of the changes we see in the gut bacteria are actually a cause or consequence of UC.”

As scientists learn more about the role of gut bacteria, the interest in treatments that focus on the microbiome is growing.

These treatments include:

  • antibiotics
  • probiotics
  • fecal microbiota transplantation (FMT)
  • dietary changes

The treatments above may help promote a healthful microbiome in people with UC, either individually or in combination with other treatments.

However, determining the effectiveness of these treatments will require further research.


Antibiotics are a type of medication that kills bacteria.

Doctors often prescribe them to people who undergo surgery for UC. They can also help treat certain complications of UC, such as abscesses.

In addition, some research suggests that antibiotics may help induce UC remission.

For example, when a group of researchers analyzed the results of past studies, it found that UC went into remission in 64% of participants who received broad-spectrum antibiotics, compared with 48% of participants who received a placebo.

However, while antibiotics may have short-term benefits for people with UC, disease-causing bacteria can become resistant to the medications over time, making the antibiotics less effective.

In addition, antibiotics can kill healthful, as well as harmful, bacteria.


Probiotics are live bacteria and other microbes that may provide health benefits. They’re sometimes combined with prebiotics. These are types of fiber that feed healthful bacteria in the gut.

When investigators from the University of Leeds reviewed research on probiotics in the treatment of UC, they found mixed results. Only some probiotics appeared to benefit people with the condition.

Specifically, people who took a product that contained multiple strains of Lactobacilli, Bifidobacteria, and Streptococcus salivarius were more likely to experience remission than those who took a placebo. This probiotic blend is sold under the brand names VSL#3 and Visbiome.

According to Dr. Arun Swaminath, director of the Inflammatory Bowel Diseases Program at Lenox Hill Hospital, in New York City, fully assessing the potential benefits and risks of probiotics will require more research.

“Many of my patients believe there is ‘no harm’ in probiotics, but I think we are only at the very beginning of understanding the long-term implications of carrying specific bacteria or combinations of bacteria,” Dr. Swaminath told MNT.


FMT involves collecting stool from a healthy donor and transplanting it into another person’s digestive system. The goal is to help “reset” the recipient’s microbiome.

Some early research suggests that FMT may help induce UC remission. However, larger and more high-quality studies are needed to assess its potential effects.

“FMT, or the transfer of donor stool from healthy individuals to those with UC, has shown limited benefit in clinical trials,” Dr. Glassner noted.

“However, benefits were seen only with stool from specific donors — and the exact composition of donor stool needed to correct the microbiome changes associated with IBD needs further evaluation,” she continued.

For now, FMT remains an experimental treatment for UC. The American Gastroenterological Association (AGA) recommend that it only be used in the context of a clinical trial.

Dietary changes

Over the long term, dietary habits play a major role in shaping the microbiome. Drastic short-term changes can also affect the balance of bacteria in the gut.

However, fully understanding how the diet affects the composition of gut bacteria, as well as symptoms and rates of remission in people with UC will require more research.

“Although there have been some small studies assessing the effect of diet in UC, there is currently not enough evidence to support one particular diet,” Dr. Glassner said.

“In general, we recommend that our patients with UC avoid diets high in sugar or highly processed foods and try to consume a healthy diet rich in fruits and vegetables,” she added.

As researchers continue to learn more about the role of bacteria in UC, new treatment options may become available.

Along the way, doctors and other scientists might eventually:

  • identify specific types of probiotics that benefit people with UC
  • design better strategies for identifying ideal FMT donors
  • develop new medications based on anti-inflammatory molecules produced by bacteria
  • develop new targeted therapies that kill disease-causing bacteria
  • design individualized treatment plans based on each person’s gut bacteria

In the meantime, the AGA advise doctors to prescribe one or more medications to treat UC. For example, a doctor might prescribe 5-aminosalicylic acid, tumor necrosis factor inhibitors, corticosteroids, and other treatments.

Although experts are still unsure of the exact cause of UC, gut bacteria likely play a role.

Certain treatments that target gut bacteria have shown some promise for reducing symptoms of UC. These include antibiotics, probiotics, and FMT.

However, evaluating the potential benefits and risks of these treatments will require further research.

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