The microbiome is home to numerous bacterial species, each contributing their own unique health-promoting properties. In fact, according to the Biochemical Journal, it has been reported that the number of bacteria in the human gut microbiota could exceed 10¹⁴ which is approximately “10 times more bacterial cells than the number of human cells and over 100 times the amount of genomic content (microbiome) as the human genome.” However, other studies report a more equal ratio of human to bacterial cells. Regardless of the exact number, the microbiome of the gut is unquestionably the largest population of microorganisms in the human body. When well-balanced, the variety of microbes gives the body fortitude and strength as it supports the immune system, fights against inflammation, provides a barrier against pathogens, helps metabolize nutrients, and produces critical nutrients among other tasks.

Bifidobacteria Throughout Life

Within this bacterial population are abundant numbers of species that belong to the genus Bifidobacteria. You might even say they are the indigenous genus of the microbiome, although their total numbers and varying species alter with age. Bifidobacteria dominate in the intestine of a breast-fed infant since the fucosylated oligosaccharides of breast milk are substrates for B. longum.  B. breve and B. bifidum are also well-colonized in infants but these species give way to B. catenulatum and B. adolescentis during the adult years. B. longum seems to remain abundant throughout life.

Bifidobacteria in Infants and Children

Bifidobacteria is the first genus of bacteria transferred from the mother’s vaginal canal, breast milk, placenta, and amniotic fluid to the infant highlighting the importance of vaginal birth and breastfeeding for establishing a healthy microbiome. Of special interest is the fact that the establishment of Bifidobacteria in an infant may be delayed if the mother has a polymorphism in the Fucosyltransferase 2 (FUT2) gene. This gene encodes for an enzyme that transfers fucose to glycans in breast milk. As mentioned earlier, glycans are metabolized by Bifidobacteria.

The antimicrobial and immunomodulatory properties of some Bifidobacteria species, such as B. breve, are vital for life stages where immunity may be weak or compromised. Infants are one example. These bacteria are even more valuable for the newly developing immune system since they are not able to transfer antibiotic resistance, which is becoming a concern among some probiotic species. B. breve is also important for the prevention of numerous gastrointestinal conditions in children including diarrhea, colic, celiac disease, obesity, and allergies.

Bifidobacteria in Adults

Though their quantities decrease with age, Bifidobacteria are equally beneficial in adults and exert numerous biological actions that can prevent some of the most common gastrointestinal conditions.

Colon Cancer

Bifidobacteria has shown promise in the prevention and/or as an adjunct therapy in the treatment of colorectal cancer in both in vitro and in vivo animal studies. In these studies, Bifidobacteria displayed anti-mutagenic activity, protected DNA from carcinogen-induced damage, and inhibited the genotoxic effects of carcinogens. Bifidobacteria were also shown to alleviate constipation and improve colon regularity in randomized, controlled trials of human subjects which offers another explanation for its ability to prevent colorectal cancer.

Diarrhea

B. longum has been shown to prevent and mitigate diarrhea caused by Clostridium difficile in in vitro and in vivo studies. Not only did Bifidobacteria therapy significantly reduce the quantity of C. difficile, but also the clostridial toxin titres dropped. Interestingly, the study found that B. longum induced an acidic pH which fostered the inhibitory actions; however, when the pH was neutralized, the therapeutic actions were lost.

Irritable Bowel Syndrome (IBS)

IBS is one of the most commonly reported gastrointestinal conditions involving abdominal pain, alternating diarrhea and constipation, bloating, and/or distension. The lack of adequate Bifidobacteria in the microbiome has been suggested as a risk factor for developing IBS and consequently, this same bacterial genus is useful in managing IBS. In fact, an inverse relationship between Bifidobacteria and abdominal pain were found such that subjects with abdominal pain “had over five-fold less Bifidobacteria compared to those without pain.” In a randomized single-blinded, placebo-controlled, crossover study of patients with IBS, a prebiotic mixture was given for 4-weeks and found to significantly increase fecal levels of Bifidobacteria. Clinical outcomes included “significant improvements in stool consistency, flatulence, bloating, composite symptom score and subjective global assessment.”

Bifidobacteria are a large genus of bacteria responsible for maintaining a healthy gut and immune system through various mechanisms. The importance of this genus cannot be underestimated and is evidenced by the fact that Bifidobacteria are the first microorganisms to populate the human gut from the moment we take our first breath.