Regarding tEPEC E2348/69, no internalized bacteria was found in the microscope fields observed. Enteropathogens may gain access to basolateral receptors and promote host cell invasion in vivo by transcytosis through M cells [46]. Alternatively, some infectious processes can cause perturbations in the intestinal epithelium, e.g., neutrophil migration during intestinal inflammation; as a consequence, a transitory destabilization in the epithelial barrier is promoted exposing the basolateral side and allowing bacterial invasion [47]. With regard to tEPEC, it learn more has been reported that an effector molecule, EspF is involved in tight junction disruption and redistribution of occludin with

ensuing increased permeability of T84 monolayers [48, 49]. Whether EspF is involved in the invasion ability of the aEPEC strains studied in vivo remains to be investigated. Figure 5 Transmission electron microscopy of polarized and differentiated T84 cells infected via the basolateral side. A) aEPEC 1551-2. B) aEPEC 0621-6. C) prototype tEPEC E2348/69. Monolayers were infected

for 6 h (aEPEC) and 3 h (tEPEC). Arrows indicate tight junction and (*) indicates a Transwell membrane pore. In conclusion, we showed that aEPEC strains expressing distinct intimin sub-types are able to Quisinostat mw Smoothened Agonist datasheet invade both HeLa and differentiated T84 cells. At least for the invasive aEPEC 1551-2 strain, HeLa cell invasion requires actin filaments but does not involve microtubules. In differentiated T84 cells, disruption of tight junctions increases the invasion capacity of aEPEC 1551-2. This observation could be significant in infantile diarrhea since in newborns and children the gastrointestinal epithelial barrier might not be fully developed [45]. As observed in uropathogenic E. coli [50], besides representing a mechanism of escape from the host immune response, invasion could also be a strategy for the establishment of persistent disease. It is possible, that the previously reported association of aEPEC with prolonged diarrhea [8] is the result of limited invasion processes. However, the in vivo relevance of our in vitro observations else remains to be established. Moreover,

further analyses of the fate of the intracellular bacteria such as persistence, multiplication and spreading to neighboring cells are necessary. Conclusion In this study we verified that aEPEC strains, carrying distinct intimin sub-types, including three new ones, may invade eukaryotic cells in vitro. HeLa cells seem to be more susceptible to aEPEC invasion than differentiated and polarized T84 cells, probably due to the absence of tight junctions in the former cell type. We also showed that actin microfilaments are required for efficient invasion of aEPEC strain 1551-2 thus suggesting that A/E lesion formation is an initial step for the invasion process of HeLa cells, while microtubules are not involved in such phenomenon.