![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
Department of Food Science and Technology, The University of Reading, Earley Gate, Reading, UK
 |
ABSTRACT |
|---|
 TOP ABSTRACT Bacterial fermentation in the...ProbioticsPrebioticsOligofructose and inulin as...Health aspects of prebioticsREFERENCES |
|---|
KEY WORDS: • prebiotics • gut microbiota modulation • inulin • oligofructose
|
Bacterial fermentation in the human colon |
|---|
|
TOPABSTRACTBacterial fermentation in the...ProbioticsPrebioticsOligofructose and inulin as...Health aspects of prebioticsREFERENCES |
|---|
). It is known that many disease states
involve bacterial metabolism. However, the gut microflora may also be
considered relevant to host welfare. Gut bacteria carry out a
multidisciplinary process known as fermentation in which dietary and
endogenously produced residues are metabolized in a process that
involves a large amount of cross-feeding by the microflora. Large
intestinal microorganisms have a strictly anaerobic metabolism; the
numbers of obligate anaerobes are many orders of magnitude higher than
those of facultative anaerobes. Numerically predominant anaerobes are
gram-negative rods belonging to the genus Bacteroides.
These bacteria can represent up to 30% of the total microbial flora.
Other groups that have been identified to date as present in high
numbers include bifidobacteria, clostridia, eubacteria, lactobacilli,
gram-positive cocci, coliforms, methanogens and dissimilatory
sulfate-reducing bacteria. It is thought that between 400 and 500
different bacterial species are present in the human large intestine. The principal substrates for gut bacterial growth are dietary carbohydrates that have escaped digestion in the upper gastrointestinal tract. In addition, amino acids can also be effective as growth substrates for colonic bacteria; bacterial secretions, lysis products, sloughed epithelial cells and mucins may also make a contribution.
A number of different microbial metabolic niches, bacterial
habitats and interrelationships occur in the large gut and respond
mainly to substrate availability, the physicochemical environment of
the gut and the metabolic capabilities of the microflora (Freter 1992
). Gut bacteria are able to metabolize substrates for
increased energy and growth. The major end-products of metabolism
are short-chain fatty acids (SCFA), mainly acetate, propionate and
butyrate, but a variety of other metabolites are also produced,
including electron sink products such as lactate, pyruvate, ethanol,
hydrogen and succinate (Table 1
).These substances are formed to maintain the redox balance during
fermentation. Electron sink products act as fermentation intermediates
because they are further metabolized to SCFA by other species. Although
the products of gut proteolysis may be generally thought of as
toxic toward host health, those of carbohydrate digestion may be
considered benign and in some cases can contribute positively (Table 1)
.
|
,1992
and 1997
, Gorbach et al. 1988
, Isolauri et al. 1991
, Kohwi et al. 1978
, Lin et al. 1989
, Sanders 1994
). For obvious reasons, there is much interest in increasing numbers and activities of beneficial bacteria in the large gut, preferably at the expense of more harmful species. A way in which this can be achieved is through dietary supplementation.
|
Probiotics |
|---|
|
TOPABSTRACTBacterial fermentation in the...ProbioticsPrebioticsOligofructose and inulin as...Health aspects of prebioticsREFERENCES |
|---|
defined a probiotic as A live
microbial feed supplement which beneficially affects the host animal by
improving its intestinal microbial balance. The probiotic
organism(s) used for human consumption are usually lactic acid
excretors.
The history of probiotics dates back as far as the first intake of
fermented milks, over 2000 years ago. However, it is probably from the
work of Metchnikoff (1907)
in the early years of this
century that the first scientific assessments of probiotics were made.
Common probiotics include the following: 1) Lactobacilli
such as Lactobacillus acidophilus, L. casei, L. delbrueckii
subsp. bulgaricus, L. reuteri, L. brevis, L. cellobiosus, L.
curvatus, L. fermentum, L. plantarum; 2)
Gram-positive cocci such as Lactococcus lactis
subsp. cremoris, Streptococcus salivarius subsp.
thermophilus, Enterococcus faecium, S. diaacetylactis, S.
intermedius; and 3) Bifidobacteria such as
Bifidobacterium bifidum, B. adolescentis, B. animalis, B.
infantis, B. longum, B. thermophilum.
Selection criteria for probiotics is an area of much debate and
should be taken into account when defining appropriate strains
(Huis In't Veld and Havennar 1991
). One important
characteristic is survival (and establishment) of the fed microorganism
after ingestion. Some studies with feces rely on phenotypic traits of
the probiotics, such as different morphologies or biochemical tests.
However, these are probably unreliable because the bacteria may exhibit
metabolic variation. Future developments in molecular techniques
directed toward gut microbiology will more clearly define the survival
characteristics of probiotics (McCartney and Gibson 1997
).
|
Prebiotics |
|---|
|
TOPABSTRACTBacterial fermentation in the...ProbioticsPrebioticsOligofructose and inulin as...Health aspects of prebioticsREFERENCES |
|---|
). Thus, the prebiotic
approach advocates the administration of nonviable entities and
therefore overcomes survival problems in the upper gastrointestinal
tract. Certain oligosaccharides that cannot be digested, except through
bacterial activity, are prebiotics. Those that contain fructose can
alter the composition of the human gut flora, by a specific
fermentation, towards a community predominated by bifidobacteria. |
Oligofructose and inulin as prebiotics |
|---|
|
TOPABSTRACTBacterial fermentation in the...ProbioticsPrebioticsOligofructose and inulin as...Health aspects of prebioticsREFERENCES |
|---|
Any food that reaches the colon such as nondigestible carbohydrates, some peptides and proteins, as well as certain lipids, is a prebiotic candidate. Nondigestible carbohydrates, in particular fructose oligosaccharides, are authentic prebiotics. Fructooligosaccharides are ß-D-fructans with degrees of polymerization (DP) varying between 2 and 60 (inulin) and 2 and 20 (oligofructose).
In vitro studies have indicated that inulin and oligofructose
have a specific fermentation (Hidaka et al. 1986
,
Wang and Gibson 1993
). This has also been confirmed in
human volunteer trials that assessed the bifidogenic effects of both
inulin and oligofructose in vivo. The influence of oligofructose
(Raftilose, P95) on the fecal bacterial composition in healthy persons
was evaluated during a 45-d feeding period in which the volunteers were
given a strictly controlled diet (Gibson et al. 1995
).
Eight volunteers participated in the experiment. They had never
suffered from any form of gastrointestinal disorder and had not taken
antibiotics for at least 3 mo before the start of the study. During the
first 5 d, subjects were given a noncontrolled diet; at that time,
a stool sample was collected for bacteriological analysis.
Subsequently, the volunteers were given the controlled diet
supplemented with 15 g of sucrose for a 15-d period. This was then
replaced by 15 g of oligofructose for a further 15 d,
followed by another period with sucrose. Stool samples were taken
periodically for bacterial enumeration. In summary, the use of
oligofructose as a replacement for sucrose in diet caused a marked
increase in bifidobacteria, whereas bacteroides, fusobacteria and
clostridia all decreased. Other bacteria tested (total aerobes, total
anaerobes, lactobacilli, coliforms and gram-positive cocci)
remained more or less unchanged. Bacteroides was the numerically
predominant genus with sucrose consumption, whereas bifidobaceria
dominated with oligofructose. Similar results were detected during the
feeding of inulin (Raftiline, ST) (Table 2). Other investigators have since confirmed the prebiotic effect of
inulin and oligofructose in vivo (Buddington et al. 1996
, Kleesen et al. 1997
).
|
|
Health aspects of prebiotics |
|---|
|
TOPABSTRACTBacterial fermentation in the...ProbioticsPrebioticsOligofructose and inulin as...Health aspects of prebioticsREFERENCES |
|---|
). In terms of the mechanism of inhibition, metabolic end products, such as acids excreted by these microorganisms, may lower the gut pH, in a microniche, to levels below those at which pathogens are able to effectively compete. Another factor that could be considered is a competitive effect by occupation of normal colonization sites (by anti-infective prebiotics or probiotic microrganisms) and competition for available nutrients. Enhanced immune function would also be a further important factor.
Many lactobacilli and bifidobacterial species are able to excrete
natural antibiotics, which can have a broad spectrum of activity (e.g.,
lactocins, helveticins, lactacins, curvacins, nisin or bifidocin). For
the bifidobacteria, our studies have indicated that some species are
able to exert antimicrobial effects on various gram-positive and
gram-negative intestinal pathogens including salmonellae,
campylobacters and Escherichia coli (Gibson and Wang 1994
).
The outbreak of E. coli 0157 in Lanarkshire, Scotland at the end of 1996 resulted in 20 fatalities. The deaths have highlighted the continuing concern about bacterial gastroenteritis to consumers, the food industry, researchers and the medical profession. In recent laboratory tests, we have also shown that some bifidobacteria exert powerful antagonistic effects towards E. coli 0157. The inhibition was variable in species of bifidobacteria, with Bifidobacterium infantis and B. longum exerting the greatest effect on E. coli 0157. The possibility exists therefore that increased levels of bifidobacteria (and consideration of the species type) in the large gut, together with other factors such as immune status, may offer improved protection.
In humans older than ~55 y, fecal bifidobacterial counts are known to
show a marked decrease in comparison to those of younger persons
(Kleessen et al. 1997
, Mitsuoka 1990
). It
may be of some relevance that the UK fatalities during the E.
coli outbreak all involved the elderly, whereas hundreds of people
in different age groups reported the infection. A potential analogy
exists with reduced pathogen resistance, decreased numbers of
bifidobacteria in the elderly and the production of natural resistance
factors. In essence, the natural gut flora may have been compromised
through reduced bifidobacterial numbers and possibly a diminished
ability to deal with the pathogen. The design of prebiotic-based
health foods for selected populations such as the elderly may therefore
have much virtue.
|
FOOTNOTES |
|---|
|
REFERENCES |
|---|
|
TOPABSTRACTBacterial fermentation in the...ProbioticsPrebioticsOligofructose and inulin as...Health aspects of prebioticsREFERENCES |
|---|
1.
Buddington R. K., Williams C. H., Chen S. C., Witherly S. A. Dietary supplementation of neosugar alters the fecal flora and decreases activities of some reductive enzymes in human subjects. Am. J. Clin. Nutr. 1996;63:709-716
2. Freter R. Factors affecting the microecology of the gut. Fuller R. eds. Probiotics: The Scientific Basis 1992:111-144 Chapman & Hall London, UK.
3. Fuller R. Probiotics in man and animals. J. Appl. Bacteriol. 1989;66:365-378[Medline]
4. Fuller R. eds. Probiotics: The Scientific Basis 1992 Chapman & Hall London, UK.
5. Fuller R. eds. Probiotics 2: Applications and Practical Aspects 1997 Chapman & Hall London, UK.
6. Gibson G. R., Beatty E. B., Wang X., Cummings J. H. Selective stimulation of bifidobacteria in the human colon by oligofructose and inulin. Gastroenterology 1995;108:975-982[Medline]
7. Gibson G. R., Macfarlane G. T. eds. Human Colonic Bacteria. Role in Physiology, Pathology and Nutrition 1995 CRC Press Boca Raton, FL.
8. Gibson G. R., Roberfroid M. B. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. J. Nutr. 1995;125:1401-1412
9. Gibson G. R., Saavedra J. M., Macfarlane S., Macfarlane G. T. Probiotics and intestinal infections. Fuller R. eds. Probiotics: Therapeutic and Other Beneficial Effects 1997:10-39 Chapman & Hall London, UK.
10. Gibson G. R., Wang X. Inhibitory effects of bifidobacteria on other colonic bacteria. J. Appl. Bacteriol. 1994;77:412-420[Medline]
11. Gorbach S. L., Barza M., Giuliano M., Jacobus N. V. Colonization resistance of the human intestinal microflora: testing the hypothesis in normal volunteers. Eur. J. Clin. Microbiol. Infect. Dis. 1988;7:98-102[Medline]
12. Hidaka H., Eida T., Takiwaza T., Tokunga T., Tashiro Y. Effects of fructooligosaccharides on intestinal flora and human health. Bifid. Microflora 1986;5:37-50
13. Huis In't Veld J.H.J., Havenaar R. Probiotics and health in man and animals. J. Chem. Technol. Biotechnol. 1991;51:562-577
14.
Isolauri E., Juntunen M., Rautanen T., Sillanaukee P., Koivula T. A human Lactobacillus strain (Lactobacillus casei sp. strain GG) promotes recovery from acute diarrhea in children. Pediatrics 1991;88:90-97
15.
Kleesen B., Sykura B., Zunft H.-J., Blaut M. Effects of inulin and lactose on fecal microflora, microbial activity, and bowel habit in elderly constipated persons. Am. J. Clin. Nutr. 1997;65:1397-1402
16. Kohwi Y., Imai K., Tamura Z., Hasimoto Y. Antitumor effect of Bifidobacterium infantis in mice. Gann 1978;69:613-618[Medline]
17. Lin S. Y., Ayres J. W., Winkler W., Sandine W. E. Lactobacillus effects on cholesterol: in vitro and in vivo results. J. Dairy Sci. 1989;72:2885-2899
18. McCartney, A. L. & Gibson, G. R. (1997) The application of prebiotics in human health and nutrition. In: Proceeding Lactic 97. Which Strains? For Which Products? pp. 59–73. Adria Normandie, Villers-Bocage, France.
19. Metchnikoff E. The Prolongation of Life 1907 William Heinemann London, UK.
20. Mitsuoka T. Bifidobacteria and their role in human health. J. Ind. Microbiol. 1990;6:263-268
21. Sanders M. E. Lactic acid bacteria as promoters of human health. Goldberg I. eds. Functional Foods: Designer Foods, Pharmafoods and Nutraceuticals 1994:294-322 Chapman & Hall London, UK.
22. Wang X., Gibson G. R. Effects of the in vitro fermentation of oligofructose and inulin by bacteria growing in the human large intestine. J. Appl. Bacteriol. 1993;75:373-380[Medline]
This article has been cited by other articles:
|
|
 |
|
  A D G Anderson, C E McNaught, P K Jain, and J MacFie Randomised clinical trial of synbiotic therapy in elective surgical patients Gut, February 1, 2004; 53(2): 241 - 245. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
