Molecular and Phenotypic Characterization of Escherichia coli O26:H8 among Diarrheagenic E. coli O26 Strains Isolated in Brazil

Abstract

ABSTRACTEscherichia colistrains of serogroup O26 comprise two distinct groups of pathogens, characterized as enteropathogenicE. coli(EPEC) and enterohemorrhagicE. coli(EHEC). Among the several genes related to type III secretion system-secreted effector proteins,espKwas found to be highly specific for EHEC O26:H11 and itsstx-negative derivative strains isolated in European countries.E. coliO26 strains isolated in Brazil from infant diarrhea, foods, and the environment have consistently been shown to lackstxgenes and are thus considered atypical EPEC. However, no further information related to their genetic background is known. Therefore, in this study, we aimed to discriminate and characterize these Brazilian O26stx-negative strains by phenotypic, genetic, and biochemical approaches. Among 44 isolates confirmed to be O26 isolates, most displayed flagellar antigen H11 or H32. Out of the 13 nonmotile isolates, 2 tested positive forfliCH11, and 11 werefliCH8positive. The identification of genetic markers showed that several O26:H11 and all O26:H8 strains tested positive forespKand could therefore be discriminated as EHEC derivatives. The presence of H8 among EHEC O26 and itsstx-negative derivative isolates is described for the first time. The interaction of three isolates with polarized Caco-2 cells and with intestinal biopsy specimen fragmentsex vivoconfirmed the ability of the O26 strains analyzed to cause attaching-and-effacing (A/E) lesions. The O26:H32 strains, isolated mostly from meat, were considered nonvirulent. Knowledge of the virulence content ofstx-negative O26 isolates within the same serotype helped to avoid misclassification of isolates, which certainly has important implications for public health surveillance.