The general principle of DGGE and TGGE is the
separation of individual rRNA genes based on differences
in their chemical stability or melting temperature.
Polyacrylamide gels consisting of a linear denaturing
gradient formed by urea and formamide are employed
for DGGE, whereas a linear temperature gradient is
used during TGGE. DGGE of PCR-amplified rRNA
gene amplicons is a useful technique for monitoring
dynamic changes in mixed bacterial populations over
time.54,55 The rRNA gene sequences from bacterial
species in a mixed culture are first amplified using
conserved bacterial primers that bracket a hypervariable
region of the rRNA gene, producing amplicons of the
same length but with differing sequences that are
specific to a given species. DGGE allows the separation
of these amplicons, producing a molecular fingerprint
of the bacterial species.54,55 DGGE and other similar
techniques have been shown to be useful to analyze
human fecal microflora.56,57 For example, DGGE may
be useful to assess the effect of antibiotic therapy on
the fecal microflora of hospitalized patients.58 Since
the bacterial microbiota of different individuals may
vary significantly the ability to provide a detailed analysis
of multiple individuals is limited.