What is Bacteroides fragilis & Is it good or bad?

May 31, 2023 2 min read

What is Bacteroides fragilis & Is it good or bad?

Bacteroides fragilis is generally considered to be a beneficial bacterium in the gut, as it is involved in many important functions such as digestion, immune system regulation, and protection against harmful microorganisms. In certain situations, B. fragilis can also become pathogenic and cause infections such as sepsis and abdominal abscesses, particularly in individuals with compromised immune systems or underlying health conditions.

Some of the functions and benefits of Bacteroides fragilis include:

  • Immune system modulation: Bacteroides fragilis has been shown to help regulate the immune system by promoting the development of regulatory T cells, which help to prevent excessive inflammation and autoimmune responses.
  • Protection against pathogens: Bacteroides fragilis produces various antimicrobial peptides that can help to protect against pathogenic bacteria in the gut.
  • Production of short-chain fatty acids: Bacteroides fragilis is capable of producing short-chain fatty acids (SCFAs), which have been shown to have various health benefits, such as improving gut barrier function and reducing inflammation.
  • Breakdown of complex carbohydrates: Bacteroides fragilis is able to break down complex carbohydrates that cannot be digested by the host, allowing for the release of nutrients that can be utilized by other members of the gut microbiota.

However, Bacteroides fragilis has been implicated in various diseases such as inflammatory bowel disease (IBD), colorectal cancer, and sepsis. Studies have shown that increased abundance of Bacteroides fragilis in the gut is associated with inflammation and the development of IBD. Furthermore, certain strains of Bacteroides fragilis have been found to carry virulence factors such as metalloproteases, lipases, and endotoxins, which can cause tissue damage and inflammation. In sepsis, Bacteroides fragilis is a common cause of infection and can lead to life-threatening complications.

Bacteroides fragilis is a complex bacterial species with both beneficial and harmful effects on the host. While it plays an important role in maintaining gut homeostasis, excessive or pathogenic strains can lead to inflammatory and disease states. Therefore, it is important to maintain a balance of Bacteroides fragilis and other gut bacteria to promote overall gut health.


Wu, H. J., & Wu, E. (2012). The role of gut microbiota in immune homeostasis and autoimmunity. Gut microbes, 3(1), 4-14.

Tursi, S. A., Tükel, Ç., & Raffatellu, M. (2017). The gut microbiome in infectious diarrhea and inflammation. Current opinion in gastroenterology, 33(6), 471-477.

He, Y., Wu, W., Wu, S., Zheng, H. M., Li, P., Sheng, H. F., ... & Zhou, H. W. (2018). Linking gut microbiota, metabolic syndrome and economic status based on a population-level analysis. Microbiome, 6(1), 172.

Round, J. L., & Mazmanian, S. K. (2009). The gut microbiota shapes intestinal immune responses during health and disease. Nature reviews immunology, 9(5), 313-323.

Gevers D, Kugathasan S, Denson LA, et al. The Treatment-Naive Microbiome in New-Onset Crohn's Disease. Cell Host Microbe. 2014;15(3):382-392. doi:10.1016/j.chom.2014.02.005

Wexler HM. Bacteroides: the good, the bad, and the nitty-gritty. Clin Microbiol Rev. 2007;20(4):593



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