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.