The MicroByte Series: Bifidobacterium longum: A Lifelong Friend

Oct 29, 2025

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6 min read

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Bifidobacterium longum is a versatile Gram-positive bacterium capable of supporting a wide array of human health functions. Driven by an advanced arsenal of carbohydrate metabolism pathways and protective polysaccharides, it effortlessly optimizes the gut environment, spreading rapidly through lifelong host microbiomes and multi-strain probiotic mixtures. Benefits range from localized inflammatory bowel disorders like ulcerative colitis to broad systemic improvements, including respiratory illness reduction and pollen allergy relief. Accurate classification leverages classic laboratory biochemistry and modern tools like advanced DNA sequencing. While optimization typically requires targeted probiotic therapy for subspecies like infantis and longum, robust safety relies heavily on screening immunocompromised individuals and tracking intestinal perforation risks.

History and naming

Bifidobacteria are important (and beneficial!) colonisers of the human gut, of which Bifidobacterium longum stands out as one of the most prolific, both in terms of beneficial potential and persistence in the body. Initially isolated by Reuter in 1963, it has since undergone an expansion of its taxonomic bounds. Also described by Reuter was ‘Bifidobacterium infantis’, similarly isolated from the infant gut. Later, Matteuzzi et al. isolated Bifidobacterium suis from pig faeces. These three species were unified into a single species in 2002 by Sakata and group, falling under B. longum, with longum, infantis, and suis serving as biotypes, meaning that they were too similar to be reliably characterised from each other at the time. In 2008, Mattarelli and group showed that despite their genotypic closeness, advances in both sequencing and biochemistry now allowed for these three musketeers to assume their role as distinguishable subspecies, still falling under the same B. longum moniker. In 2015, B. longum subsp. suillum was proposed as the fourth subspecies, being isolated again from pig faeces, but has since reportedly also been isolated from the human infant gut. The last subspecies to be added was Bifidobacterium longum subsp. iuvenis (meaning ‘of child’), isolated and characterised by Modesto et. al in 2023.

Colonisers- Friendly microbes that successfully attach, settle down, and multiply in a specific part of the body, such as the gut or skin.

Taxonomic bounds- The official scientific boundaries, rules, and categories used to accurately classify and group living organisms into specific families, genera, and species.

Faeces- Poop or solid waste material excreted from the body after food has been fully digested and nutrients have been absorbed.

Species- A specific group of closely related organisms that share distinct common characteristics and a high degree of genetic similarity.

Sequencing- An advanced laboratory method used to read and decode the exact order of chemical building blocks (the genetic code) in an organism's DNA or RNA.

Biochemistry- The branch of science that studies the complex chemical processes, substances, and reactions that naturally take place inside living organisms.

Subspecies- A distinct biological sub-category within a species, grouping organisms that share unique genetic variations but are still closely related.

Role in the Body

Bifidobacterium longum is famously the most predominant species in the gut of infants, but is retained even in adulthood, though its levels reduce. In fact, research now suggests that B. longum is a lifetime companion, having been isolated from the guts of the elderly and even centenarians. In the gut, it plays an important role in carbohydrate metabolism, with a genome packed with pathways that allow it to digest both animal- and plant-derived carbohydrates. It is capable of producing vital metabolites like SCFAs, which have diverse roles in overall health, and some strains produce molecules that have anti-inflammatory properties. They also help maintain the gut bacterial lining through the production of polysaccharides that protect bacteria from stressors in the gut and also facilitate communication between the bacteria themselves.

SCFA (Short-Chain Fatty Acids)- Beneficial organic acids produced when friendly gut bacteria ferment dietary fiber; they serve as primary fuel for gut cells and help manage body-wide inflammation.

Anti-inflammatory properties- The natural ability of a specific food, compound, or medicine to actively soothe and reduce swelling, heat, and irritation inside body tissues.

Polysaccharides- Complex carbohydrates made up of long, interconnected chains of sugar molecules that serve as a vital energy source or dietary fiber for gut bacteria.

Applications

B. longum subsp. infantis is known to have multiple benefits when administered to neonates or infants. This strain has shown promise in the handling of gastroschisis, a congenital defect of the GI tract, through restoration of the gut microbiota, and may help in the prevention of infant diarrhea. However, more rigorous trials are required to confirm these effects. B. longum subspecies mixtures, along with other Bifidobacteria, have also shown promising impact in reducing childhood IBS symptoms and improving quality of life measures. Similarly, multi-strain mixtures of which longum and infantis strains were part also helped reduce ulcerative colitis relapse. It is unclear as to the individual contributions of B. longum strains, as the beneficial impacts could be due to high amounts of bacteria delivered and multiple mechanisms through which each component strain acts beneficially. B. longum BB536 also showed gut and immune health benefits when administered to healthy infants. This same strain also showed promise in reducing the duration of infection and symptoms of respiratory illnesses in toddlers. In concert with other Bifidobacteria and Lactobacilli, strains of B. longum have also been shown to positively impact skin health, reducing dermatitis scores and improving eczema rates in children.

Similarly, B. longum has several benefits when supplemented to adults, over a variety of conditions. In the GI tract, standalone or multi-strain probiotics containing B. longum strains have been shown to improve symptoms of and reduce inflammation and dysbiosis related to common bowel inflammatory disorders like ulcerative colitis and Crohn’s disease, as well as improve quality of life and gastrointestinal symptoms of irritable bowel syndrome (IBS). B. longum BB536 has also been shown to reduce pollen allergy symptoms in Japanese adults. In combination with other Bifidobacteria and Lactobacillus strains, strains of B. longum were also shown to reduce the duration of the common cold and even improve mood and cognition. B. longum lysate applied topically was also shown to improve skin hydration and reduce sensitivity.

Bifidobacterium longum may also have health benefits for the elderly, such as regulating bowel movements and improving gut microbiota and immune parameters. As with children and adults, combinations with other probiotic strains also came with benefits, such as improved cognitive function and mood.

Neonates- Newborn infants, specifically during their first 28 days of life, who are in a highly delicate stage of immunological and physical development.

Gastroschisis- A rare birth defect where an infant is born with an opening or hole in the abdominal wall, causing the intestines to develop outside the baby's body.

Multi-strain mixtures- Probiotic supplements or formulas that combine several different types or specific strains of beneficial bacteria to provide a wider range of health perks.

Immune health- The overall strength, balance, and daily efficiency of the body's natural defense network in detecting and destroying harmful germs.

Dermatitis- A general medical term for skin irritation or inflammation, typically causing redness, swelling, and uncomfortable, itchy patches.

Eczema- A chronic inflammatory skin condition that causes the skin to become dry, intensely itchy, red, cracked, and highly prone to infections.

Dysbiosis- An unhealthy, disrupted state of balance in the microbial communities of the body, where harmful microbes outnumber the beneficial ones.

Ulcerative colitis- A chronic, long-term inflammatory bowel disease that causes painful sores (ulcers) and severe swelling solely within the lining of the large intestine.

Crohn’s disease- A chronic inflammatory bowel disease that triggers deep, widespread swelling anywhere along the entire digestive tract, from the mouth to the anus.

Pollen allergy- An overreactive immune response triggered by inhaling microscopic powder (pollen) from trees, weeds, or grasses, causing sneezing and watery eyes.

Lysate- A purified fluid mixture containing the contents of intentionally broken-open cells, often used in skincare to deliver beneficial bacterial components without live bacteria.

Risks

While several clinical trials now exist showing the potential benefits of Bifidobacterium longum supplementation for various aspects of human health, larger and longer trials would help further establish the efficacy of different B. longum strains. Many trials also involve combinations of probiotics, which render the individual impacts and mechanisms of individual B. longum strains unclear. Thus, single-strain interventions also require further study. Strain-level uses must also be understood, as different subspecies and strains of this bacterium have different functionalities. Analyses of safety show that this microbe is generally safe, but long-term studies are also required to monitor outcomes. Complications of human infection caused by Bifidobacteria are rare, but the existence of isolated cases necessitates precaution by practitioners in the case of patients with underlying conditions or those immunocompromised or at risk of having intestinal perforation.

Efficacy- The true capability or clinical power of a specific treatment, drug, or probiotic strain to produce a proven, desired health benefit under real conditions.

Immunocompromised- Having a significantly weakened or damaged immune system, making it much harder for the body to fight off infections and illnesses.

Intestinal perforation- A life-threatening medical emergency where a physical hole or tear develops completely through the structural wall of the stomach or intestines.

Taxonomic Classification

Domain: Bacteria

Phylum: Actinomycetota (or Actinobacteria)

Class:Actinomycetia

Order:Bifidobacteriales

Family:Bifidobacteriaceae

Genus:Bifidobacterium

Species: Bifidobacterium longum

Subspecies:Bifidobacterium longum subsp. infantis, Bifidobacterium longum subsp. iuvenis, Bifidobacterium longum subsp. longum, Bifidobacterium longum subsp. suillum, Bifidobacterium longum subsp. Suis

Microbe Profile

Gram Stain: +ve

Shape: Rod

Spore formation: No

Biofilm formation: Yes

Oxygen requirement: Anaerobic

Optimal temperature: 37°C to 42°C

Optimal pH: 6.5- 7.0

Nutrient usage: Heterofermentative

-Antara Arvind

Reference

Guo, H., Fan, M., Hou, T., Li, Y., Wang, S., Wang, X., Peng, H., Wang, M., Wu, T., & Zhang, Y. (2023). Efficacy and Safety of Bifidobacterium longum Supplementation in Infants: A Meta-Analysis of Randomized Controlled Trials. Foods, 12(24), 4451. https://doi.org/10.3390/foods12244451

Mattarelli, P., Bonaparte, C., Pot, B., & Biavati, B. (2008). Proposal to reclassify the three biotypes of Bifidobacterium longum as three subspecies: Bifidobacterium longum subsp. longum subsp. nov., Bifidobacterium longum subsp. infantis comb. nov. and Bifidobacterium longum subsp. suis comb. nov. INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY, 58(4), 767–772. https://doi.org/10.1099/ijs.0.65319-0

Mills, S., Yang, B., Smith, G. J., Stanton, C., & Ross, R. P. (2023). Efficacy of Bifidobacterium longum alone or in multi-strain probiotic formulations during early life and beyond. Gut Microbes, 15(1). https://doi.org/10.1080/19490976.2023.2186098

Modesto, M., Ngom-Bru, C., Scarafile, D., Bruttin, A., Pruvost, S., Sarker, S. A., Ahmed, T., Sakwinska, O., Mattarelli, P., & Duboux, S. (2023). Bifidobacterium longum subsp. iuvenis subsp. nov., a novel subspecies isolated from the faeces of weaning infants. INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY, 73(10). https://doi.org/10.1099/ijsem.0.006013

Odamaki, T., Bottacini, F., Kato, K., Mitsuyama, E., Yoshida, K., Horigome, A., Xiao, J., & Van Sinderen, D. (2018). Genomic diversity and distribution of Bifidobacterium longum subsp. longum across the human lifespan. Scientific Reports, 8(1). https://doi.org/10.1038/s41598-017-18391-x

Tena, D., Losa, C., Medina, M. J., & Sáez-Nieto, J. A. (2014). Peritonitis caused by Bifidobacterium longum: Case report and literature review. Anaerobe, 27, 27–30. https://doi.org/10.1016/j.anaerobe.2014.03.005

Zhang, Z., Hou, Q., Wang, Y., Xiang, F., & Guo, Z. (2022). Evaluation of Bacterial Diversity and Evolutionary Dynamics of Gut Bifidobacterium longum Isolates Obtained from Older Individuals in Hubei Province, China. Microbiology Spectrum, 10(1). https://doi.org/10.1128/spectrum.01442-21

Cheng, H., Liu, J., Mei, L., Liu, W., Yang, F., Ma, X., Zhang, Y., Xie, Y., Zhang, Y., & Xiong, Y. (2025). Optimization of Medium Composition for High Cell Density Culture of Bifidobacterium longum HSBL001 Using Response Surface Methodology. MicrobiologyOpen, 14(4). https://doi.org/10.1002/mbo3.70027

Chen, J., Chen, X., & Ho, C. L. (2021). Recent development of probiotic bifidobacteria for treating human diseases. Frontiers in Bioengineering and Biotechnology, 9. https://doi.org/10.3389/fbioe.2021.770248

BIFIDOBACTERIUM LONGUM

PROBIOTICS

Frequently Asked Questions

Why is Bifidobacterium longum considered a lifelong companion rather than just an infant gut bacterium?

While it is the most predominant microbe in infants, it adapts and persists throughout a human host's entire lifespan. Scientific research has successfully isolated this resilient bacterium from adults, the elderly, and even healthy centenarians.

How has the taxonomic classification of Bifidobacterium longum subspecies evolved over the years?

Three separate species were unified as identical biotypes in 2002 before advanced sequencing and biochemistry re-established them as distinct subspecies in 2008. Since then, newer subspecies like suillum and iuvenis have further expanded its lineage.

What major metabolic functions does Bifidobacterium longum perform to support human gut health?

Its genome is heavily packed with pathways optimized to digest a wide variety of both plant- and animal-derived carbohydrates. Through this process, it produces vital anti-inflammatory short-chain fatty acids (SCFAs) and protective structural polysaccharides.

How does the infantis subspecies specifically support newborn health conditions like gastroschisis?

This specialized probiotic strain shows great clinical promise in actively restoring healthy gut microbiota balance in fragile neonates. Its targeted administration can alleviate infant diarrhea and effectively support the management of congenital abdominal wall defects.

Although Bifidobacterium longum is generally safe, which specific patient populations require clinical precaution?

Medical practitioners must exercise caution when recommending supplementation to patients who are heavily immunocompromised. Extra precaution is also strictly required if a patient has an underlying risk of developing a life-threatening intestinal perforation.

BugSpeaks®

BugSpeaks®, developed by Leucine Rich Bio Pvt Ltd, South Asia’s first microbiome company, is headquartered in Bengaluru, India. Since 2014, the company has pioneered advanced analytics to analyze complex genomics data. Collaborating with leading research institutes globally, Leucine Rich Bio has leveraged its expertise to create BugSpeaks®, South Asia’s first gut microbiome test.

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