A method fo detecting large numbers of isolates of enterotoxigenic Escherichia coli is described in which the genes encoding th enterotoxins are detected, rather than the toxins themselves. Radiolabeled fragments of DNA encoding the heat-labile (LT) or heat-stable (ST) toxins were used as hybridization probes for homologous DNA sequences in E. coli colonies grown and lysed in situ on nitrocellulose filters. The LT probe detected all of 31 E. coli strains producing ST and LT or only LT, while the ST probe detected 12 of 17 strains producing only ST and three of 26 strains producing ST and LT. These results suggest that the LTs produced by different isolates of E. coli are homologous and that human isolates of E. coli produce at least two heterologous STs detectable in the infant mouse assay. The hybridization method also detected the presence of enterotoxigenic E. coli in bacterial growth in directly spotted stools from patients with acute diarrhea.

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The clinical characteristics of disease due to enterotoxigenic Escherichia coli (ETEC) were determined in 88 adult males admitted to a hospital in Dacca, Bangladesh, with moderate to severe dehydration. Persons infected with ETEC strains producing both heat-labile toxin (LT) and heat-stable (ST) toxin had more dehydration and acidosis, longer duration of illness, and greater stool volume than persons infected with strains producing only ST. Tetracycline therapy, evaluated in 63 cases, resulted in slightly earlier termination of illness in patients with LT-ST strains but had no effect on illness in the patients with ST strains. In both groups of patients tetracycline shortened the duration of excretion of organisms. Because of its limited effectiveness and the generally excellent response of ETEC diarrhea to rehydration therapy alone, tetracycline is not warranted for use in treatment of ETEC diarrhea in adults in this population.

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We determined whether enterotoxigenic Escherichia coli diarrhea could be diagnosed by direct examination of stools for heat-labile (LT) and heat-stable (ST) enterotoxins. The Y-1 adrenal cell and an enzyme-linked immunosorbent assay (ELISA) detected LT in 85 and 93%, respectively, of stool specimens obtained from adults with acute diarrhea from whom an LTand ST-producing organism had been isolated. Furthermore, the ELISA assay detected LT in 8 of 35 stool specimens from which no LT-producing E. coli had been isolated. The infant mouse assay was utilized to detect ST in these stool specimens and was found to be an insensitive method, showing positive results in only 36% of the specimens from which an ST-producing organism was isolated. Further studies are warranted to determine the diagnostic value of direct detection of LT in stools, especially by the ELISA method.

Escherichia coli strains produce at least two heat-stable enterotoxins, STa and STb. STa is well known to be important in the pathogenesis of human diarrheal disease; the role of STb has not been defined. Fifty-two E. coli strains recovered from human diarrheal illness in northeast Brazil or Bangladesh were examined in weaned porcine ligated intestinal segments for STb activity. A total of 113 E. coli strains from human diarrheal disease in northeast Brazil and 28 E. coli strains from Bangladesh were examined for DNA hybridization to a STb gene probe. None of these strains produced STb as detected by enterotoxic activity or by the gene probe. We also examined adult human ileal mucosa for responses to STb in the Ussing chamber in vitro. In contrast to piglet jejunum, which consistently responds electrogenically to crude STb, human ileal tissue showed no response to STb but responded electrogenically to theophylline (10 mM). These results suggest that STb-producing E. coli strains are not a major cause of diarrheal illness in humans.