Late Establishment of the Attaching and Effacing Lesion Caused by Atypical Enteropathogenic Escherichia coli Depends on Protein Expression Regulated by Per

Enteropathogenic Escherichia coli (EPEC) is classified as typical (tEPEC) or atypical (aEPEC) based on the presence or absence of the E. coli adherence factor plasmid (pEAF), respectively. The hallmark of EPEC infection is the formation of the attaching and effacing (A/E) lesions on the gut mucosa. We compared the kinetics of A/E lesion formation induced by aEPEC and tEPEC. The examination of infected HEp-2 cells clearly demonstrated delayed A/E lesion formation by aEPEC in comparison to tEPEC. This delay was associated with the expression of locus of enterocyte effacement (LEE)-encoded virulence factors (i.e., intimin and EspD). Indeed, the insertion of a plasmid containing perABC, a transcriptional regulator of virulence factors involved in A/E formation, into aEPEC strains increased and accelerated the formation of A/E lesions. Interestingly, the enhanced expression and translocation of LEE-encoded proteins, such as those expressed in LEE5 (intimin) and LEE4 (EspD), in aEPEC (perABC) was independent of bacterial adhesion. The secretion kinetics of these two proteins representing LEE5 and LEE4 expression corre-lated with A/E lesion formation.We conclude that the lack of Per in the regulation network of virulence genes is one of the main factors that delay the establishment of A/E lesions induced by aEPEC strains. Enteropathogenic Escherichia coli (EPEC) is one of the maincausative agents of infantile acute diarrhea in developing countries (1–4). The hallmark of EPEC pathogenesis is the forma-tion of a histopathological lesion in the intestinal epithelium known as attaching and effacing (A/E) (5). Distinctive features o