Identification of enterotoxigenic Escherichia coli in patients with diarrhea in Asia with three enterotoxin gene probes

Abstract

A total of 984 enterotoxigenic Escherichia coli (ETEC) and 733 non-ETEC isolated from patients with diarrhea in Asia (one isolate per patient) were examined for homology with radiolabeled fragments of DNA encoding heat-labile toxin (LT) or heat-stable toxin of porcine (ST-P) or human (ST-H) origin. A total of 246 ETEC that produced LT and ST as determined by the Y-1 adrenal and suckling mouse assays were homologous with the LT probe. Of these 246 LTST ETEC, 156 (63%) were homologous with the ST-H, 46 (19%) were homologous with the ST-P, and 44 (18%) were homologous with both probes. A total of 401 LT ETEC were homologous with the LT probe. Of 337 ST ETEC identified by the suckling mouse assay, 244 (72%) were homologous with the ST-H, 84 (25%) were homologous with the ST-P, and 9 (3%) were homologous with both probes. None of the 733 isolates that were non-enterotoxigenic as determined by the Y-1 adrenal and suckling mouse assays was homologous with genes coding for enterotoxin. Four isolates (not included among the 984 ETEC examined) that were initially considered to produce LT because sterile culture supernatants produced rounding of Y-1 adrenal cells were not homologous with the LT probe. The sterile culture supernatants of these four isolates caused rounding after 8 h and subsequent destruction after 24 h of Y-1 adrenal tissue cultures. This effect was not inhibited by convalescent human cholera antiserum, Swiss Serum Institute cholera antitoxin, or antiserum to purified LT. These isolates were also negative in the Biken test previously used to identify LT-producing E. coli. The DNA hybridization technique with three enterotoxin gene probes was developed as a specific technique to identify ETEC in large numbers of specimens in Asia.