Novel Aggregative Adherence Fimbria Variant of Enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) organisms belong to a diarrheagenic pathotype known to cause diarrhea and can be characterized by distinct aggregative adherence (AA) in a stacked-brick pattern to cultured epithelial cells. In this study, we in-vestigated 118 EAEC strains isolated from the stools of Danish adults with traveler’s diarrhea. We evaluated the presence of the aggregative adherence fimbriae (AAFs) by a multiplex PCR, targeting the four known major subunit variants as well as their usher-encoding genes. Almost one-half (49/118) of the clinical isolates did not possess any known AAF major fimbrial subunit, despite the presence of other AggR-related loci. Further investigation revealed the presence of an AAF-related gene encoding a yet-uncharacterized adhesin, termed agg5A. The sequence of the agg5DCBA gene cluster shared fimbrial accessory genes (usher, chaperone, and minor pilin subunit genes) with AAF/III, as well as the signal peptide present in the beginning of the agg3A gene. The complete agg5DCBA gene cluster from a clinical isolate, EAEC strain C338-14, with the typical stacked-brick binding pat-tern was cloned, and deletion of the cluster was performed. Transformation to a nonadherent E. coli HB101 and complementa-tion of the nonadherent C338-14 mutant with the complete gene cluster restored the AA adhesion. Overall, we found the agg5A gene in 12 % of the 118 strains isolated from Denmark, suggesting that this novel adhesin represents an important variant. During the past decades, enteroaggregative Escherichia coli(EAEC) has emerged as an important pathogen, causing di-arrhea in adults and children in both industrialized and nonindus-trialized countries (1–5). Moreover, EAEC has also been linked t