Identification of enterotoxigenic Escherichia coli using alkaline phosphatase-labeled synthetic oligodeoxyribonucleotide probes.

Alkaline phosphatase-conjugated synthetic oligodeoxyribonucleic acid probes were used to detect enterotoxigenic Escherichia 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 X 10(6) toxigenic bacteria by colony hybridisation. No cross reactivity was observed between probes. When 197 clinical isolates of Escherichia 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 toxigenic Escherichia coli.