Identification of enterotoxigenic Escherichia coli by colony hybridization using three enterotoxin gene probes

The applicability of examining clinical specimens with a DNA hybridization technique for genes encoding enterotoxins was examined using enterotoxigenic Escherichia coli (ETEC) that produced both heat-labile toxin (LT) and heat-stable toxin (ST) (24 isolates), ETEC that produced LT only (17 isolates), and ETEC that produced ST only (22 isolates) from Thailand. ETEC was identified with Y-l adrenal cell and suckling mouse assays. All were homologous with radiolabeled fragments of DNA encoding LT or ST of porcine origin (ST-P) or of human origin (ST-H). Strains of ETEC that produced ST only from rural Thailand were homologous with the ST-H probe only, whereas strains isolated in Bangkok were homologous with the ST-H probe, the ST-P probe, or both probes. The hybridization technique detected ETEC in all stool samples of patients with diarrhea from whom ETEC was isolated and in ETEC-inoculated water containing other species of bacteria. The DNA hybridization assay is useful for characterizing and identifying environmental sources of ETEC.