Biochemical and Genetic Diversity of EnterotoxigenicEscherichia coliAssociated with Diarrhea in United States Students in Cuernavaca and Guadalajara, Mexico, 2004–2007

Abstract

Background. Molecular characterization of Escherichia coli with use of the random amplified polymorphic DNA (RAPD) assay allows the determination of clonal origin and geographic clustering. Methods. Presumed enterotoxigenic Escherichia coli (ETEC) from 213 adults with travelers' diarrhea acquired in Mexico during the summer months of 2004–2007 were studied. Biochemical testing strips determined a 7-digit fingerprint on the basis of 21 biochemical reactions. E. coli producing enterotoxin were evaluated for clonality by RAPD assay. Dendrograms were developed using Pearson correlations with ⩾80% similarity to determine clonal groups. Results. Of the presumed ETEC, 85% were confirmed to be E. coli on the basis of biochemical analysis. Other enterotoxigenic bacteria included Citrobacter species (9%) and other coliforms (all ⩽2%). RAPD analysis with primers 1247 and 1254 determined 24 ETEC clonal groups containing 2–9 subjects each, of which 15 spanned the 4 years and 8 spanned both cities. Conclusions. Complete biochemical evaluation of E. coli-like, enterotoxigenic organisms is crucial in ETEC identification. In addition, other enterotoxigenic organisms identified should be studied further for their role in enteric disease. Travelers to Mexico are exposed to a large pool of different ETEC strains from multiple sources, with a small number of dominant types showing a widespread and persistent reservoir of infection.