Chemistry Reference
In-Depth Information
is common among elderly people and may lead to small intestinal bacterial over-
growth, chronic diarrhea, and malabsortion.
1,2
Atrophic gastritis may also affect the
bioavailability of calcium, ferric iron, and vitamin B
12
and contribute to the defi-
ciency of these minerals and vitamins. Also colonic transit may slow with aging,
but the individual variation is high. Constipation, which is a common symptom in
elderly people, may be partly explained by the decreased intestinal motility. Another
factor linked with constipation is low fecal weight, which has been reported among
the elderly people. The slow intestinal transit has been associated also with increased
bacterial putrefaction and, consequently, increased levels of ammonia and phenols
in the gut. The immune system is often adversely affected by the aging process
and the resistance to diseases may be decreased. More detailed description about
the aging-related physiological and functional changes in the GI tract can be found
elsewhere.
3,4
The microbiological changes in the GI tract due to aging have been
characterized and are discussed in detail below after the short introduction on mod-
ern microbiota assessment techniques. Further in this chapter, we discuss the possi-
bilities of counteracting the aging-associated changes in the GI tract with probiotics
and prebiotics. There is experimental and clinical evidence that they may support
antibacterial and barrier-enhancing actions, have antiinflammatory effects, as well
as enhance immunity.
5,6
16.1.2 Assessment of Microbiota
The knowledge on intestinal microbiota has been gained over the years by using
various microbiological techniques. Although early studies relied entirely on culti-
vation, today molecular biological techniques complement the culturing techniques
and also allow us to study the microbiota in a culture-independent way.
7
Cultivated colonies can be identified by genetic fingerprinting by, for example,
ARDRA, RAPD, or PFGE (amplified ribosomal DNA restriction analysis, randomly
amplified polymorphic DNA, pulsed field gel electrophoresis, respectively). Whereas
the above-mentioned techniques usually require some in-house optimization and
standardization, fingerprinting by automated ribotyping and (partial) 16S rDNA
sequencing are user-friendly choices. The major advantage of PFGE is that it has the
highest discriminatory power, and the advantages of RAPD and ARDRA include
easy performance and relatively low cost. For the phenotypic molecular typing of
cultivated bacteria cell membrane fatty acid profiling, the so-called FAME (fatty acid
methyl ester identification) analysis is a popular and well-standardized technique.
Entire bacterial communities can be profiled directly from samples in a culture-
independent manner by using techniques, such as PCR-TGGE or PCR-DGGE and
T-RFLP (polymerase chain reaction coupled with temperature or denaturing gradient
gel electrophoresis and terminal restriction fragment length polymorphism, respec-
tively). Construction of 16S rDNA libraries by PCR and subsequent cloning and the
sequencing of clones have also been extensively used. Specific microbial groups can
be traced by using specific primers and probes in PCR and fluorescent
in situ
hybrid-
ization (FISH), respectively. Recently, major methodological improvements for the
microbiota analysis have been achieved by the development of bacterial high-density
