Rapid differentiation of enterotoxigenic Escherichia coli that produce heat-stable and heat-labile toxins by frequency-pulsed electron capture gas-liquid chromatography analysis of diarrheal stool specimens

Abstract

Thirty-three stool specimens from infants in the village of Tamooh near Cairo, Egypt, were studied by frequency-pulsed electron capture gas-liquid chromatography (FPEC-GLC). In 13 of the diarrheal cases, the suspected causative agent isolated was Escherichia coli which produced heat-stable toxin (ST), and in 10 other cases E. coli that produced heat-labile toxin (LT) were isolated. Ten control stool samples, collected from infants from whom no pathogenic organisms were isolated, were analyzed at the same time. Comparisons also were made against healthy control stools from individuals in the United States who had been previously analyzed by FPEC-GLC (Brooks et al., J. Clin. Microbiol. 20:549-560, 1984). The stools were suspended in water and centrifuged, and the supernatant was extracted with organic solvents and derivatized to form electron-capturing derivatives of carboxylic acids, hydroxy acids, alcohols, and amines. Results from the study showed distinct differences among the FPEC-GLC profiles of E. coli ST-positive stools, of E. coli LT-positive stools, and of the control stool samples. An unidentified compound appearing in the ether-soluble hydroxy acid fraction from E. coli ST-positive stools was tentatively identified by mass spectrometry as 6-methoxy-2-hydroxyhexanoic acid. 6-Methoxy-2-hydroxyhexanoic acid was found in all stools that contained E. coli ST but was not present either in stools from which E. coli LT was isolated or in control samples. 6-Methoxy-2-hydroxyhexanoic acid may prove to be an important marker for use in the identification of E. coli ST. In addition to 6-methoxy-2-hydroxyhexanoic acid, the carboxylic acid, alcohol, and amine FPEC-GLC profiles obtained from stools were very different between these two organisms. The data indicate that FPEC-GLC analysis of diarrheal stool specimens might be a rapid way to distinguish diarrhea caused by E. coli ST, E. coli LT, Clostridium difficile, and rotavirus.