Bifidobacteria are a group of Gram-positive, anaerobic, and non-motile bacteria that are commonly found in the human gastrointestinal tract. These are some important cellular and colonial characteristics, plus typical requirements for growth.

Cellular characteristics:

  • Bifidobacteria are rod-shaped bacteria with a length of 2-3 µm and a width of 0.5-1 µm.
  • They are non-spore-forming and non-flagellated.
  • They have a thick peptidoglycan layer in their cell wall and lack an outer membrane.
  • They are able to ferment carbohydrates and produce lactic acid, acetic acid, and other organic acids.

Colony characteristics:

  • Bifidobacteria form white or cream-colored colonies on agar plates.
  • The colonies are typically small (0.5-1.0 mm in diameter) and convex with a smooth surface.
  • Bifidobacteria colonies are often surrounded by a clear zone of inhibition due to the production of organic acids that inhibit the growth of other bacteria.

Growth requirements:

  • Bifidobacteria are obligate anaerobes, meaning they require an oxygen-free environment to grow.
  • They grow best at a pH of 6.0-7.0 and at a temperature of 37 °C.
  • Bifidobacteria are fastidious bacteria and require a complex medium containing a variety of nutrients such as amino acids, vitamins, and minerals to grow.
  • They are able to utilize a wide range of carbohydrates, including lactose, fructose, and oligosaccharides.

There are more than 50 known species of bifidobacteria, but some of the most common and well-studied species include:

  1. Bifidobacterium adolescentis … from the human large intestine, and is known for its ability to break down complex carbohydrates.
  2. Bifidobacterium animalis … from intestinal tracts of animals, but can also be found in human faeces. It has been shown to have probiotic properties and is used in many commercial probiotic products.
  3. Bifidobacterium bifidum … from the human large intestine and is one of the first bacteria to colonise the gut of infants. It has been shown to have beneficial effects on the immune system and may help prevent gastrointestinal infections.
  4. Bifidobacterium breve … from human milk and has been shown to be beneficial for the health of infants. It has also been shown to have probiotic properties in adults.
  5. Bifidobacterium lactis … from dairy products and is used in many commercial probiotic products. It has been shown to have beneficial effects on the immune system and may help alleviate symptoms of lactose intolerance.
  6. Bifidobacterium longum … from the human gastrointestinal tract and has been shown to have probiotic properties. It may help improve gut health and alleviate symptoms of irritable bowel syndrome.
Figure 1: B. longum subsp. longum … colonial morphology (A), cellular morphology (B) and SEM image (C) – image source: Zhao et al. (2021) in Frontiers of Microbiology 12:756519.

Several species of bifidobacteria are commonly used as probiotics in food and supplements, including:

  1. Bifidobacterium bifidum (Figure 2)
  2. Bifidobacterium lactis
  3. Bifidobacterium longum (Figure 1)
  4. Bifidobacterium animalis subsp. lactis
  5. Bifidobacterium breve
  6. Bifidobacterium infantis
Figure 2: SEM image of B. bifidum – image source: Ali et al. (2015) in the Iranian Journal of Pharmaceutical Research 13:843.

These species have been shown to have probiotic properties and may help support digestive health, boost the immune system, and alleviate certain gastrointestinal conditions. However, the effectiveness of specific strains and doses of bifidobacteria as probiotics may vary depending on the individual and the specific health condition being targeted. Here are some of the potential human health benefits of bifidobacteria:

  1. Digestive health: Maintain digestive health by producing enzymes that help break down complex carbohydrates, and by producing lactic acid and other compounds that help create a favorable environment for beneficial bacteria to thrive.
  2. Immune system support: Modulate the immune system, potentially reducing the risk of allergies, infections, and autoimmune diseases.
  3. Mental health: Produce neurotransmitters such as 4-aminobutanoic acid (commonly referred to as GABA) and serotonin, which can help regulate mood and alleviate symptoms of anxiety and depression.
  4. Metabolic health: Improve insulin sensitivity, reduce inflammation, and improve lipid profiles, potentially reducing the risk of metabolic disorders such as type 2 diabetes.
  5. Infant health: Bifidobacteria are among the first bacteria to colonize the gut of infants, and have been shown to play a key role in promoting healthy development of the immune system, digestive system, and brain.

There’s no doubt that bifidobacteria are important members of the human gut microbiota, and they have been associated with a number of digestive health benefits. Bifidobacteria may also help reduce the incidence and severity of diarrhea associated with antibiotic use, as demonstrated in a randomized controlled trial (Szajewska, Kołodziej, & Gieruszczak-Białek, 2015).

We may not think of gut microbiota as playing a role in mental health, but indeed they do. It is understood that bifidobacteria may regulate mood and alleviate symptoms of anxiety and depression by producing certain neurotransmitters, such as GABA and serotonin. For example, it’s been found that Bifidobacterium infantis administration to rats resulted in increased GABA receptor expression in the brain, leading to a reduction in anxiety-like behavior (Bravo et al., 2011). In humans, results from a randomized controlled trial were that administration of a probiotic mixture containing Bifidobacterium bifidum, Bifidobacterium lactis, and Lactobacillus acidophilus for four weeks significantly reduced symptoms of depression and anxiety compared to placebo (Messaoudi et al., 2011a). In another study, the results indicated that administration of a probiotic containing Bifidobacterium longum and Lactobacillus helveticus for eight weeks improved mood and cognitive function in healthy volunteers (Messaoudi et al., 2011b).


Bravo, J. A., Forsythe, P., Chew, M. V., Escaravage, E., Savignac, H. M., Dinan, T. G., … & Cryan, J. F. (2011). Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proceedings of the National Academy of Sciences of the USA 108:16050-16055.

Messaoudi, M., Violle, N., Bisson, J. F., Desor, D., Javelot, H., & Rougeot, C. (2011b). Beneficial psychological effects of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in healthy human volunteers. Gut Microbes 2:256-261

Messaoudi, M., Lalonde, R., Violle, N., Javelot, H., Desor, D., Nejdi, A., … & Cazaubiel, M. (2011a). Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects. British Journal of Nutrition 105:755-764.

Szajewska, H., Kołodziej, M., & Gieruszczak-Białek, D. (2015). Systematic review with meta-analysis: Lactobacillus rhamnosus GG in the prevention of antibiotic-associated diarrhoea in children and adults. Alimentary Pharmacology & Therapeutics 42:1149-1157.