The presence of the sseJ gene in S . Typhi promotes the disruption of the epithelial monolayer. HT-29 cells were grown in transwells for 12-15 days. Polarised HT-29 cells were apically infected with the wild type S. Typhi or the respective complemented strains. TER 1 h post-infection reported as a percentage of the initial TER value and is expressed as the means ± SD of three different experiments, each performed in duplicate. The percentages of TER values from cells infected with S. Typhi carrying each empty plasmid (pSU19 or pCC1) showed no differences with respect the wild type strain (data not shown).