Evidence for Gardnerella vaginalis uptake and internalization by squamous vaginal epithelial cells: implications for the pathogenesis of bacterial vaginosis

Bacterial vaginosis (BV), a common condition seen in premenopausal women, is associated with preterm labor, pelvic inflammatory disease, and delivery of low birth weight infants. Gardnerella vaginalis is the predominant bacterial species associated with BV, although its exact role in the pathology of BV is unknown. Using immunofluorescence, confocal and transmission electron microscopy, we found that VK2 vaginal epithelial cells take up G. vaginalis after exposure to the bacteria. Confocal microscopy also indicated the presence of internalized G. vaginalis within vaginal epithelial cells obtained from a subject with BV. Using VK2 cells and 35S labeled bacteria in an invasion assay, we found that a 1 h uptake of G. vaginalis was 21.8-fold higher than heat-killed G. vaginalis, 84-fold compared to Lactobacillus acidophilus and 6.6-fold compared to Lactobacillus crispatus. Internalization was inhibited by pre-exposure of cells to cytochalasin-D. In addition, the cytoskeletal protein vimentin was upregulated in VK2 cells exposed to G. vaginalis, but there was no change in actin cytoskeletal polymerization/rearrangements or vimentin subcellular relocalization post exposure. Cytoskeletal protein modifications could represent a potential mechanism for G. vaginalis mediated internalization by vaginal epithelial cells. Finally, understanding vaginal bacteria/host interactions will allow us to better understand the underlying mechanisms of BV pathogenesis.