Identification of enterotoxigenicEscherichia coli using alkaline phosphatase-labeled synthetic oligodeoxyribonucleotide probes

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Abstract
Alkaline phosphatase-conjugated synthetic oligodeoxyribonucleic acid probes were used to detect enterotoxigenicEscherichia coli strains containing either the heat stable or heat labile toxin genes. Both of the synthetic probes detected as little as 5 ng of purified plasmid DNA bearing the appropriate toxin gene. In addition, both probes could detect 5 × 106 toxigenic bacteria by colony hybridisation. No cross reactivity was observed between probes. When 197 clinical isolates ofEscherichia coli were examined for toxigenicity using bioassays, 13 heat stable and 17 heat labile toxin strains were identified. Of the 13 heat stable toxin strains, 12 were positive using the heat stable toxin synthetic probe (sensitivity, 92 %; specificity, 98 %) while 16 of 17 bioassay heat labile toxin positive samples were identified using the heat labile toxin synthetic probe (sensitivity, 94 %; specificity, 97 %). Alkaline phosphatase-conjugated synthetic probes with high sensitivity and specificity should provide a rapid means of identifying toxigenicEscherichia coli.