immunoassays. While striving for antibodies that are sufficiently broad
in their specificity to recognize all strains of the desired target organism,
it is difficult to avoid the problem of cross reactivity with organisms
other than those under investigation.
10.6.2 DNA/RNA Methodology
All biochemical, immunological and other characteristics used in the
detection of micro-organisms are governed directly or indirectly by the
base sequences encoded in the organism’s genome. The specificity of this
information can now be mobilized to provide methods capable of
identifying genera, species or even strains within a species. Nucleic acid
probes can be designed which recognize and bind (hybridize) to specified
regions of either chromosomal or plasmid DNA or to RNA, and the
region chosen to give the desired level of specificity. Thus, for example,
ribosomal RNA contains both conserved and variable regions, the
Figure 10.4 Sandwich ELISAs. (a) Competitive sandwich ELISA, (b) direct sandwich
ELISA
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