Adherence properties and adhesin-encoding genes detected in enteroaggregative Escherichia coli (EAEC)

Enteroaggregative Escherichia coli (EAEC) is an enteropathogen that harbors a set of adhesins responsible for mediating adherence to epithelial cells in a stacked brick-like arrangement termed aggregative adherence (AA) pattern and is one of the main pathogens isolated from diarrheal patients worldwide. In the present study, we characterized 140 EAEC isolates, obtained from stool samples of individuals with diarrhea in Brazil, based on their phylogeny, adherence properties, and presence of major pilin-encoding genes for aggregative adherence fimbriae (AAF) and aggregate-forming pili (AFP). The majority of the EAEC isolates were assigned into the phylogroups A (57.9%), B1 (18.6%), and D (17.1%), while the serotypes O86:H2 (7.9%), O153:H2 (6.4%), O168:H4 (4.3%), O175:H28 (4.3%), and O73:H18 (3.6%) were the most frequent. A total of 78.6% of the isolates produced the AA pattern on HeLa cells and/or on the glass coverslips, and 69.3% were classified as biofilm producers on polystyrene. Interestingly, three isolates (2.1%) produced chain-like adherence (CLA), which is characterized by the formation of bacterial cell chains on the surface of epithelial cells. Major pilin-encoding genes were detected with the following frequencies: aggA (37.8%), agg3A (14.3%), agg4A (13.6%), agg5A (13.6%), aafA (9.3%), and afpA (8.6%). Additionally, four isolates (2.8%) harbored agg3A and agg5A concomitantly. Of note, all EAEC isolates producing CLA harbored agg4A. Our data indicate that the EAEC isolates studied have originated from several E. coli backgrounds, leading to the emergence of a heterogeneous group of enteropathogen. Moreover, we highlighted a distinct EAEC subgroup that produces CLA on infected cells. IMPORTANCE: Enteroaggregative Escherichia coli (EAEC) is a major cause of both acute and persistent diarrhea worldwide, with a particularly high prevalence in developing countries. In this study, we performed a comprehensive molecular and phenotypic characterization of 140 EAEC isolates obtained from both pediatric and adult patients with diarrheal disease. Our findings support the knowledge that EAEC represents a heterogeneous group of isolates that have emerged from distinct E. coli genetic backgrounds, primarily within phylogroups A, B1, and D. Although most isolates exhibited the characteristic aggregative adherence (AA) pattern on infected epithelial cells, a subset displayed the chain-like adherence (CLA) phenotype and carried the aatA, aggR, and agg4A genes. This scenario highlights the need for continuous surveillance to monitor the emergence of novel virulence strategies employed by EAEC to adhere to host cells and cause disease.