We assessed alterations in barrier function following infection with wild-type S. flexneri 2a and S. dysenteriae 1 and their isogenic attenuated strains CVD 1208S and CVD 1256, respectively, by measuring the transepithelial flux of fluorescently labeled Dextran (FITC-Dextran, 4 kDa) or Bovine Serum Albumin (FITC-BSA, 66 kDa). Here, ALB is linked to infection.