Transmission electron microscopy of infected polarized and differentiated T84. A) aEPEC 1551-2, B) aEPEC 0621-6 and C) prototype tEPEC E2348/69. Monolayers were infected for 6 h (aEPEC) and 3 h (tEPEC). aEPEC 1551-2 and 0621-6 were selected because, according to the data in Fig. 1B, they presented an average invasion index as compared to the other strains studied. Arrows indicate bacterial-containing vacuoles.