Invasion of differentiated intestinal Caco-2 cells is a sporadic property among atypical enteropathogenic Escherichia coli strains carrying common intimin subtypes.

Atypical enteropathogenic Escherichia coli (aEPEC) strains produce attaching-effacing (AE) lesions on enterocytes due to the interaction of the adhesin intimin with its translocated receptor. aEPEC strain 1551-2 was previously shown to invade HeLa and T84 cells by means of the uncommon intimin subtype omicron. Other aEPEC strains carrying uncommon intimin subtypes have also been shown to invade differentiated T84 intestinal cells. In this study, seven aEPEC strains carrying the most common EPEC intimin subtypes (alpha, beta, and gamma) were evaluated regarding the ability to invade differentiated intestinal Caco-2 cells. Although all strains adhered to and promoted AE lesions, the numbers of cell-associated bacteria varied significantly between the different strains regardless of the intimin subtype (P < 0.05). Gentamicin protection assay and transmission electron microscopy analyses showed that in comparison with the invasive strain 1551-2, only one strain (aEPEC EC423/03, intimin beta) was invasive (P = 0.05). Although both strains persisted intracellularly until 48 h, the number of viable bacteria of EC423/03 decreased, whereas that of 1551-2 increased significantly up to 24 h and then decreased. In conclusion, invasiveness is a sporadic property among aEPEC strains carrying some common intimin subtypes.