Bifidobacterium consists of about 45 species and belongs to phylum Actinobacteria. They are indigenous components of human and animal gastrointestinal micro flora. They are gram +ve, non-sporing, non-motile, rod-shaped and catalase-negative anaerobes, which produce acetic acid and lactic acids from carbohydrates without the generation of carbon-dioxide¹. Genus can be distinguished from other bacterial groups  like Lactobacilli, Actinomycetes and anaerobic Corynebacterium  by Fructose-6-phosphate phosphoketolase (F6PPK ) assay^2,3.

Tissier isolated Bifidobacterium from healthy breastfed infants in the year 1899. It is also isolated from infant feces, breast milk, cow’s milk, yogurts, sour cream, cheese desserts, ice cream and powdered milk⁴. Bifidobacteria species is predominant in the guts of breastfed infants^5,6,7.

Bifidobacteria turn out medicinal drug chemicals, enzymes, vitamins B and K and carboxylic acid which decreases the growth of fungus, also helps in digestion and facilitates absorption of nutrients^8,9. Probiotics are “live microorganisms that, once consumed in sufficient quantity, offer health benefits to their host”¹⁰ .

Selection criteria for probiotics

While choosing the probiotics strain for human purpose, it ought to be isolated from the microflora that probably stick to the human intestinal wall. The strain ought to be properly isolated and known before use^11,12,13,14 .

There are a variety of standards to be followed throughout while choosing microorganism for probiotics. Strains of eubacterium and Bifidobacterium are usually used. Members of alternative genus like Bacillus licheniformis have conjointly been investigated to be used as probiotics^7,15. Selected strains should be non-pathogenic and non-toxic. Bifidobacterium is generally considered safe^16,7. Before choosing alternative probiotics, toxicologic studies should be performed¹⁷.

Commercially important probiotics

The world population have become alert to the relation between nutrition and physiological state. Probiotic cultures are exploited extensively by the dairy farm business as tools for the production of novel purposeful products. Historically probiotics are incorporated in dairy products, milk and cheese; besides milk-based probiotic products, attempts are being made to use and develop nonmilk probiotic products. A variety of carriers of probiotics have been examined recently together with edible spreads and meat. New product like cereals, fruits and vegetables are in   the developmental stages¹⁸ .

The Beneficial effects of probiotics
Probiotics offer familiar health benefits like prevention and amelioration of intestine diseases. They have hypocholesterolemic, anticancer and antioxidative effects. Probiotics are reported to be helpful in atopic dermatitis, wound and scar-healing, and possess skin-rejuvenating properties^19,20. The major health attributes of probiotics are shown in Fig.1.

Fig. 1. Health attributes of Probiotics

Bifidobacterium
Bifidobacterium species are one of the most abundant microbes in natural microflora of colon. The bacteria in 25% of adult feces and 80% of infant feces are Bifidobacterium^35,36. Bifidobacterium species plays an important role in human health by prevention of intestinal infections, decreasing cholesterol, stimulating immune system therfor decreasing cancer risk³⁴. The beneficial effects of Bifidobacterium sp
(Table 1).

Table (1):
Beneficial effects of Bifidobacterium sp

Health benefits of Bifidobacterium
Bifidobacteria in diarrhoea
Many studies have reported Bifidobacteria  is used to treat various gasterointestinal disorders²¹. This is mainly due to the administration of B. breve and B. longum. A review containing 8,014 infants, children and adult with acute diarrhea were given probiotics which contains Bifidobacterium strains, the result were found to reduce the duration of diarrhea²². Antibiotic associated diarrhea in children and adult patients are also recommended to take probiotics along with antibiotics this have proven antibiotic donot interfere with the probiotics²³.

Bifidobacteria  in colorectal cancer
Probiotics supress the growth of bacteria which convert procarcinogens into carcinogens thereby reducing the amount of carcinogens in the intestine¹⁷.  Many species of Bifidobacterium have been found to reduce the incidence of tumour in the liver, colon, small intestine and mammary gland of rats²⁴. Bacterial enzymes like ג–glucuronidase and nitroreductase play a vibrant role in the development of cancer by hydrolaysing carcinogenic compounds. Studies have reported that probiotics, including species of Bifidobacteria, decrease the activity of these enzymes thereby reducing various cancers²⁵.

A recent study has reported that probiotic supplements containing B.  longum and other species of Bifidobacterium, suppress the total number of colon cancer cells in rats²⁶. Many studies have concluded that certain strains of probiotics can be used as an adjuvant in cancer treatment²².

Bifidobacteria in allergic disorders
The shift of Th1/Th2 cytokine balance towards Th2 response is associated with allergic disorders which cause  the activation of Th2 cytokines and release of interleukin 4, 5 and 13 and also IgE production²⁷. Studies have reported that long term consumption of Bifidobacterium lactis significantly reduces the allergic symptoms in children. A study evaluated the clinical and immunological changes of atopic dermatitis after consuming probiotics containing B.animalis and L.acidophilus found to play a major role in the treatment of atopic dermatitis^28,29,30,31 .

Bifidobacterium in Hepatic Encephalophathy

Probiotics found to be effective against the treatment of hepatic encephalophathy³².  Intake of different Lactobacillus and Bifidobacterium strains in an acute liver injury rat model has shown various effects on bacterial translocation and hepatocellular damage³³. In another study five days of probiotic therapy with Bifidobacterium strains in alcoholic patients have significantly lowered AST and ALT activity at the end of treatment³⁴ .

Characterization of  Strain

Bile and acid tolerance

Gastric acid and bile play a significant role  in the body’s defence  against ingested microorganisms. In order to use bacteria as probiotics, it should be made to resist bile salts¹⁹. Bile salt plays a fundamental role in the defence mechanism of the gut.

Production of antimicrobial substances

Variety of antimicrobial substances has been produced by probiotic bacteria. Some of those compounds includes short fatty acids, bacteriocins, hydrogen peroxides etc. These have the ability to compete against gastrointestinal microbes and thereby inhibit pathogen bacteria^37,38.

Bifidobacteria produce antimicrobial proteins such as bacteriocins, which are substances for the inhibition of food borne pathogens³⁹. Bacteriocins promotes antimicrobial activity through pore formation which causes cell lysis and prevents biosynthesis of cell wall⁴⁰.

Adhesion properties of Bifidobacteria
The adhesion onto mucin is used to evaluate the ability of the strains to colonise  the intestine. This property is an important factor for the selection of probiotics⁴¹. Mucin in the intestine of hosts provides protection from enteric pathogens via steric hindrance specific binding for viruses and bacteria. Certain Bifidobacterium strains like B. bifidum, B. longum has afcA and engBF genes which express mucin degrading glycosidase ⁴².

Carbohydrate metabolism
Bifidobacteria are saccharolytic  and play a significant role in the fermentation of carbohydrates in colon. It can also ferment different sources of carbon such as xylo-oligosaccharides. Bifidobacteria degrade hexose sugars through  “bifid shunt” a metabolic pathway. In this, Fructose 6 phosphoketolase is broken down to fructose 6 phosphate in the presence of inorganic phosphate⁴³. F6PPK assay using different chemicals like CTAB and Triton X-100 (Sigma) is a reliable test for genus identification of bifidobacteria ³⁵.

Culture media for Bifidobacterium species
Due to the non-availability of appropriate selective media, the isolation of Bifidobacterium sp from various niches has been a difficult task. Several media for the enumeration of Bifidobacterium sp are tested, and Wilkins Chalgren’s agar, containing 100 mg/L Mupirocin, is used as selective medium of Bifidobacterium species from milk and cheese ⁴⁴. Reinforced Clostridial Agar and MRS Agar containing cysteine, Columbia agar medium containing lithium chloride and sodium propionate are used as selective media in dairy products and in quality control laboratories⁴⁵. MTPY medium is used for isolating Bifidobacteria from hens’ gastrointestinal tract^46,47.

A study by Wasilewska et al (2003)⁴⁸ developed another selective medium from milk: Raffinose Propionate lithium Mupirocin. In the year 2003, Ewa isolated Bifidobacteria from infant feces by two newly-modified Gerche’s media:

1).One with stimulating Bifidobacteria growth maltodextring instead of lactose.

2).Addition of lithium chloride (3g/L) and Penicillin G, Sodium salt (50 U/L).

Culture medium used in different samples for the enumeration of Bifidobacterium sp is shown in Table 2.

Table (2):
Culture medium used in different samples for enumeration of Bifidobacterium sp

Species of Bifidobacteria
More than thirty two Bifidobacterium species have been identified by scientists^49,50. Distribution of principal species of Bifidobacterium is represented in Table 3 and major findings on Bifidobacterium sp in Table 4.

Table (3):
Distribution of species of Bifidobacterium

Table (4):
Major Findings on Bifidobacterium species

Bifidobacterium Sp in probiotic foods
Bifidobacterium bifidum grew better in milk under anaerobic conditions than standard strains. This strain gave the best results when it was added at 5-10% to milk and when stored at pH 5.0-5.3, and storage at lower pH adversely affected growth and acid production. Kanbe etal (2007)⁵¹ reviewed the characteristics of Bifidobacterium spp. growth factors and evidence for its beneficial effects on protein metabolism, vitamin metabolism, fecal excretion, kidney problems and the immune response. Fernandes etal (1987) ⁵²and Guo etal (2010)⁵³ mentioned that Lactobacillus spp. along with B. bifidum constituted health benefits. Hughes and Hoover (2011)⁵⁴ discussed Bifidobacteria, a group of lactose-utilizing bacteria, with emphasis on classification. Recent research has focused on these organisms and the benefits obtained from the ingestion of bifid-containing food products. Misra and Kuila (2001)⁵⁵ summarized the biological activities, the role of Bifidobacteria, preparation and the antimicrobial activity and therapeutic properties of bifidus milk. Consumption of bifidus milk with a high number (108 cfu/g) of this organism will provide L (+)-lactic acid, antibiotic factor and live Bifidobacteria in addition to other nutritional components. The combined action of these factors will create favorable conditions for the proliferation of intestinal Bifidobacteria, and discourage the growth of harmful organisms ⁵⁶.Bifidobacteria and functional foods
Functional foods are “food containing some health promoting components, also called as super food, designer foods etc., and functional by means of adding probiotics¹⁰. Certain Lactic acid bacteria including Lactobacillus and Bifidobacterium genus are used as functional ingredients in probiotic food products⁹. Bifidobacterium sp, isolated from different food products, is shown in Table 5. The main challenge associated with the application of probiotic cultures in functional food is their viability during processing. B. animalis subsp. lactis BB-12 is a widely used probiotic strain in food manufacture because of its viability⁵⁷.

Table (5):
Bifidobacterium species isolated from different food products

General features of Bifidobacterial genomes
The NCBI knowledge base presently holds 254 publicly-out Bifidobacteria ordering sequences, of which lxi represents a complete ordering sequence. 3 or a lot of complete ordering sequences are Bifidobacterial species, like B. animalis, B. adolescentis B. breve,B.bifidum,B. longum and B. angulatum. The typical size of a Bifidobacterial ordering is 2.2 Mb, with appreciable differences in size. For instance, B.indicum LMG11587 has an ordering size 1.73 Mb, whereas B. scardoviiJCM12489 has 3.16 Mb. Bifidobacterium orderings generally have 52–58 RNA genes per genome, except the ordering of B. longum subsp. infantis ATCC15697, which has seventy nine tRNA genes. The amount of rRNA operons among Bifidobacterial genomes generally ranges from 2 to 5, and it has been recommended that the amount of rRNA operons present on a genome correlate to the variation of a specific species to environmental conditions^58,59.