Bifidobacteria are anaerobic, gram-positive, irregular or branched rod-shaped bacteria that are commonly found in the intestines of humans and most animals and insects. They were first isolated and described over one hundred years ago from human feces and were quickly associated with a healthy GI tract due to their numerical dominance in breast fed infants compared to bottle fed infants (Tissier, 1899; 1906). While they were first grouped in the genus Bacillus, the genus Bifidobacterium was proposed in the 1920’s (Orla-Jensen, 1924). However, there was not a taxonomic consensus for this new genus and for much of the 20th century, they were classified in the genus Lactobacillus, due to their rod-like shapes and obligate fermentative characteristics. However, the accumulation of studies detailing DNA hybridizations, GC content and unique metabolic capabilities resulted in the resurrection of the Bifidobacterium genus, which was included in the eight edition of Bergey’s manual in 1974. They are characterized by a unique hexose metabolism that occurs via a phosphoketolase pathway often termed the ‘bifid shunt’. Fructose-6-phosphate phosphoketolase (F6PPK) is a key enzyme of the ‘bifid shunt’ and its presence is the most common diagnostic test for this genus, as it is not present in other gram-positive intestinal bacteria. The genus is comprised of 31 characterized species, 11 of which have been detected in human feces (Tannock, 1999). B. longum is often the dominant species detected in humans and is the only species to regularly harbor plasmids. It is a leading member of the probiotic bacteria due to numerous studies that have provided a growing body of evidence for its role in a myriad of potential health benefits. These include diarrhea prevention in antibiotic treated patients (Black et al., 1991); cholesterol reduction (Dambekodi and Gilliland, 1998); alleviation of lactose intolerance symptoms (Jiang et al., 1996); immune stimulation (Takahashi et al., 1998); and cancer prevention (Reddy and Rivenson, 1993). This myriad of potential health benefits attributed to the B. longum species clearly illustrates that this species possesses many very interesting characteristics. The potential cancer prevention ability is very interesting and studies have suggested this may be due to the protection from different carcinogens, including methyl quinolines (Reddy and Rivenson, 1993), heterocyclic amines (Sreekumar and Hosono, 1998), nitrosamines (Grill et al., 1995), and azomethane (Singh et al., 1997). It is anticipated that identification and functional analysis of the genetic determinants involved in these activities will strengthen the evidence for the involvement of B. longum in these significant health benefits. Selection of suitable strains for probiotic purposes is very difficult as inherent characteristics of strains of B. longum that are necessary for its survival and competition in the human large intestine are currently very poorly understood (O’Sullivan, 2001). The use of the sequenced genome in microarray analysis should reveal the pertinent traits that are important for these bacteria to attain dominance in these complex ecosystems. http://genome.jgi-psf.org/draft_microbes/biflo/biflo.home.html Bifidobacterium longum keeps the human digestive system running smoothly One of the most important residents in the human gastrointestinal tract, B. longum keeps the digestive system running smoothly, blocks the growth of harmful bacteria, and boosts the immune system. The organism ferments sugars into lactic acid and has many health benefits for humans and is often the dominant bacterium found in humans. It is a Gram-positive, anaerobic, branched rod-shaped bacterium. Researchers have identified a number of proteins that are specialised to help B. longum interact with the human host and persist against harmful bacteria and future reseach will now closely look at which genes allow B. longum to live in different environments such as dairy products, vegetables and the human gastrointestinal tract. Bifidobacterium longum is among the first to colonise the sterile digestive tract of newborns and predominates in breast-fed infants. Formula-fed infants have a different microflora, and this may be related to the higher risk of diarrhea and allergies in these babies. Recognising the many benefits to good health, lactic acid bacteria are included in dairy foods and taken as supplements in powder, liquid extracts, or tablets and this has also resulted in people supplementing their diets with these microbes, which are also called probiotics (meaning 'in favour of life'). Live cultures in yogurt have been used as a remedy for hundreds of years to support immune function and doctors recommend bacterial supplements to patients who take antibiotics, suffer from bacterial, viral or fungal infections or have various digestive problems. Other potential uses of B. longum are being investigated in separate studies. Japanese researchers showed that the microbe might be useful as a gene delivery vector for cancer therapy. They injected the bacterium into the tail veins of rats and demonstrated that B. longum is accumulated in the tumor. Comparative studies of lactic acid bacteria may lead to better understanding the microbes' roles in food fermentation and human health. http://www.ebi.ac.uk/2can/genomes/bacteria/Bifidobacterium_longum.html |
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