Bifidobacteria (sometimes referred to as Bifido species) is a type of bacteria that are naturally found in the human microbiome and have been labelled as friendly, probiotic or commensal bacteria – that is, they are a natural part of our microbiome and are thought to confer benefits on their host.
As well as being a normal part of the human microbiome, Bifodobacteria is, as far as we know currently, one of the most important types of bacteria to support a healthy microbiome.
Bifidobacteria are defined as gram-positive, meaning that they respond positively to a die and retain its colour. They are also non-motile (non-moving), often branched (Y-shaped), but also rod-shaped and anaerobic (do not require oxygen for growth).
Bifidobacteria utilises a unique pathway, called the bifid shunt, and a key enzyme is known as fructose-6-phosphate phosphoketolase (F6PPK) to carry out their functions. This pathway and enzyme are used in identifying the presence and actions of this species of bacteria.
Whilst they are not genetically linked to and therefore not technically classified as lactic acid bacteria, Bifidobacteria produce lactic acid (not gas) as their main end-product. In this way, this type of bacteria is also found in and used to produce yoghurts, cheeses and other fermented foods.
Types of Bifidobacteria
Bifidobacteria are part of the class of bacteria known as Actinobacteria and more than 60 different species have been discovered by scientists to date through a process known as genome sequencing. Some of the main species found in the human gut microbiome include:
Gram-positive, anaerobic, rod-shaped bacteria found in the large intestines of most mammals, including humans.
Bifidobacterium animalis and Bifidobacterium lactis are both subspecies of Bifidobacterium animalis.
Gram-positive, non-motile, anaerobic, rod-shaped bacteria found in clusters, pairs and independently. Mostly found in the colon, lower small intestine and breast milk and known to metabolise human milk oligosaccharides (HMOs).
Gram-positive, anaerobic, rod-shaped, non-motile bacteria that forms branches with the bacteria around it. Can metabolise some human milk oligosaccharides (HMOs) and feed on carbohydrates released by other bacteria.
Gram-positive, anaerobic, rod-shaped bacteria considered to be one of the earliest colonisers of the GI tract of infants, with some sub-species (such as subsp. infantis) being responsible for HMO metabolism.
Where are Bifidobacteria found?
As they are anaerobic (live in the absence of oxygen), Bifidobacteria are normally found in the intestines, the mouth and the vagina in mammals, including humans, as these are all anaerobic environments.
Since Bifidobacteria were first isolated from the faeces of breast-fed infants in 1899, they have been thought to be among the first species of microbes to colonise the human gastrointestinal (GI) tract following birth.
Bifidobacteria dominate the total gut bacterial population of healthy breast-fed infants (up to 90%), much more so than those who are bottle-fed.
By the time we are adults, Bifidobacteria represent only around 3-6% of the total gut microbial population – and this proportion declines further as we age.
What do Bifidobacteria do?
As they are found in far greater numbers in breast-fed infants, Bifidobacteria are believed to be specific for digesting sugars (carbohydrates) in breast milk (galacto-oligosaccharides) that are important to support a baby’s growth.
Gut wall development
Bifidobacteria are also thought to help the development of the gut wall as it becomes less permeable and to prevent the development of infection via the gut wall.
Reduced dominance after weaning
The dominance of Bifidobacteria decreases following weaning as the increase in solid food intake leads to an increase in the diversity of bacteria in the microbiome.
The sugars (carbohydrates) that the Bifidobacteria digest are fermented to produce lactic acid, which is then used by the body for a number of functions, the main one of which is thought to be brain metabolism.
It is thought that the ability to utilise a large variety of substances for energy means that Bifidobacteria are able to compete with other GI bacteria and thus maintain their position as one of the primary strains of bacteria found in the gut microbiome throughout our lives.
Metabolise plant-derived sugars
The Bifidobacteria population itself adapts as solid food is introduced, to include species that can metabolise plant-derived sugars, such as Bifidobacterium longum, subsp. longum. In addition, some Bifidobacteria (such as B. bifidum) alter their function towards mucin degradation, supporting the turnover of mucous cells on the gut lining.
Bifidobacteria in supplements
As a result of their beneficial activity and the fact that they have GRAS status (Generally Recognised as Safe), Bifidobacteria strains are often found in friendly bacteria supplements, either on their own or in combination with other strains (often Lactobacillus and Acidophilus).
These supplements may be used to restore good bacteria in the gut that may have been affected by gastrointestinal infections (diarrhoea and vomiting) or medications, such as antibiotics.