Cytolethal distending toxin-producing Escherichia coli clinical isolates from Mexican children harbor different cdt...

Cytolethal distending toxins (CDTs), encoded by cdtABC genes, have DNase activity leading to cellular and nuclear distention, resulting in actin remodeling, irreversible cell cycle arrest and apoptosis of target cells. PCR cdt-positive Escherichia coli strains have been isolated from children with diarrhea worldwide. However, toxin production and biological activity of cdt⁺ strains are rarely confirmed. Here, we characterized the biological activity of cdt⁺ E. coli of clinical isolates from Mexican children with severe diarrhea and its relationship with the harbored cdt type. Ten isolates from seven patients containing cdt⁺ E. coli, one isolate from a patient containing cdt^- E. coli, and a prototype CDT-producing E. coli were used to determine the harbored cdt-type, cell distention, actin remodeling and cell cycle arrest on epithelial cells. Three isolates harbored cdt type I, one type II, two type III, two type IV and two simultaneously type II and III. Lysates from eight cdt⁺ E. coli isolates caused cell distention, actin cytoskeletal remodeling and cell cycle arrest but two isolates from the same patient harboring simultaneously cdt type II/III did not. The cdt genes were necessary and enough to cause the cytolethal distending pathology. Mutants in cdtAB_IC (O86:H34 strain; cdt-I) and cdtAB_IIC (isolate; cdt-II) were complemented by cdtAB_IIC genes and both recovered the CDT-induced phenotypes. Transformation of E. coli BL21 by cdtAB_IIC genes caused this cytolethal distending pathology. These data indicate that cdt + E. coli isolates are potentially dangerous bacteria to cause serious epithelial cell damage and cell death to aggravate childhood diarrhea.