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Photo: Dan O'Sullivan,
University of Minnesota |
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.
References:
- Black, F., K.
Einarsson, A. Lidbeck, K. Orrhage, and C. E. Nord, 1991. Effect of lactic
acid producing bacteria on the human intestinal microflora during ampicillin
treatment. Scand. J. Infect. Dis. 23:247-254.
- Dambekodi, P.
C., and S. E. Gilliland. 1998. Incorporation of cholesterol into the
cellular membrane of Bifidobacterium longum. J. Dairy Sci. 81:1818-1824.
- Grill, J. P.,
J. Crociani, and J. Ballongue. 1995. Effect of bifidobacteria on nitrites
and nitrosamines. Letts. Appl. Microbiol. 20:328-330.
- Jiang, T. A.,
A. Mustapha, and D. A. Savaiano. 1996. Improvement of lactose digestion
in humans by ingestion of unfermented milk containing Bifidobacterium
longum. J. Dairy Sci. 79:750-757.
- O’Sullivan,
D. J. 2001. Screening of intestinal microflora for effective probiotic
bacteria. J. Ag. Food Chem. 49:1751-1760.
- Orla-Jensen, S.
1924. La classificationdes des bactéries lactiques. Lait 4, 468-474.
- Reddy, B. S.,
and A. Rivenson. 1993. Inhibitory effect of Bifidobacterium longum on
colon, mammary, and liver carcinogenesis induced by 2-amino-3-methylimidazo[4,5-f]quinoline,
a food mutagen. Cancer Res. 53:3914-3918.
- Singh, J. A. Rivenson,
M. Tomita, S. Shimamura, N. Ishibashi, and B. S. Reddy. 1997. Bifidobacterium
longum, a lactic acid-producing intestinal bacterium inhibits colon
cancer and modulates the intermediate biomarkers of colon carcinogenesis.
Carcinogenesis 18:833-841
- Sreekumar, O.,
and A. Hosono. The antimutagenic of a properties of a polysaccharide
produced by Bifidobacterium longum and its cultured milk against
some heterocyclic amines. Can. J. Microbiol. 44:1029-1036.
- Takahashi, T.
E. Nakagawa, T. Nara, T. Yajima, and T. Kuwata. 1998. Effects of orally
ingested Bifidobacterium longum on the mucosal IgA response of
mice to dietary antigens. Biosci. Biotechnol. Biochem. 62:10-15.
- Tannock, G. W.
1999. Identification of lactobacilli and bifidobacteria. Curr. Issues
Mol. Biol. 1(1):53-64.
- Tissier, H. 1900.
Recherches sur la flore intestinale des nourrissons (etat normal et
pathologique) Paris Thèses: 1-253.
- Tissier, H. 1906.
Traitement Des infections intestinales par la méthode de la flore
bactérienne de l’intestin. Critical Reviews of the Society
for Biology 60:359-361.
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