Pilus backbone contributes to group B Streptococcus paracellular translocation through epithelial cells

We have recently shown that group B Streptococcus (GBS) crosses the epithelial barrier by a paracellular route. Here, we show that, although deletion of the pilus backbone protein did not affect GBS adhesiveness, it reduced the pathogen's capacity to transcytose through differentiated human epithelial cells. In addition, contrary to our expectation, a strain with a mutant pilus ancillary protein and reduced adhesiveness translocated through the epithelial monolayer in a fashion identical to that of the isogenic wild-type strain. To monitor the localization of pili during GBS paracytosis, we performed 3-dimensional confocal experiments. By this approach, we observed that pili located in the intercellular space ahead of translocating bacteria. These results were also confirmed by a novel in vitro model of GBS infection in which bacteria bind to epithelial surfaces against the action of gravitation. These findings suggest a dual role for pilus components during the critical steps leading to GBS dissemination in the host.