Plesiomonas shigelloides enters polarized human intestinal Caco-2 cells inan in vitro model system

This study provides the first definitive evidence that the gram-negative ba cterium Plesiomonas shigelloides adheres to and enters eukaryotic intestina l host cells in vitro. P. shigelloides is increasingly regarded as an emerg ing enteric pathogen and has been implicated in intestinal and extraintesti nal infections in humans. However, the establishment of its true role in en teric disease has been hindered by inadequacies in experimental design, def iciencies in clinical diagnosis, and the lack of an appropriate animal mode l. In this investigation, an in vitro system was used to evaluate plesiomon ad pathogenesis. Differentiated epithelium-derived Caco-2 cell monolayers i noculated apically with 12 isolates of P. shigelloides from clinical (intes tinal) origins were examined at high resolution using transmission electron microscopy. Bacterial cells were observed adhering to intact microvilli an d to the plasma membrane on both the apical and the basal surfaces of the m onolayer, The bacteria entered the Caco-2 cells and were observed enclosed in single and multiple membrane-bound vacuoles within the host cell cytopla sm. This observation suggests that initial uptake may occur through a phago cytic-like process, as has been documented for many other enteropathogens. P. shigelloides also was noted free in the cytosol of Caco-2 cells, suggest ing escape from cytoplasmic vacuoles, Differences in invasion phenotypes we re revealed, suggesting the possibility that, like Escherichia coli, P, shi gelloides comprises different pathogenic phenotypes.