Identification of a Cluster of Strains Bearing a New Adhesin among Genetically Diverse Enterotoxigenic Escherichia coli Isolates of Serogroup O20

About one-third of the enterotoxigenic Escherichia coli isolates lack any of the known colonization factors. Among this group, those of serogroup O20 are the most frequently isolated in Argentina. By combining analysis of adhesion to Caco-2 cells, random amplified polymorphic DNA, and pulsed-field gel electrophoresis techniques, we were able to identify three sets of closely related strains with different binding properties. Further analysis of the most prevalent group revealed that all these isolates expressed the recently described adhesin CS22.