Klebsiella pneumoniae Translocates across the Intestinal Epithelium via Rho GTPase- and Phosphatidylinositol 3-Kinase/Akt-Dependent Cell Invasion

Abstract

Klebsiella pneumoniaeis an important pathogen that causes hospital-acquired septicemia and is associated with the recent emergence of community-acquired pyogenic liver abscess (PLA). Clinical typing suggests thatK. pneumoniaeinfections originate from the gastrointestinal reservoir. However, the underlying mechanism remains unknown. Here, we have sought to determine howK. pneumoniaepenetrates the intestinal barrier. We identified that bacteremia and PLA clinical isolates adhered to and invaded intestinal epithelial cells. Internalization ofK. pneumoniaein three different human colonic cell lines was visualized by confocal microscopy and three-dimensional (3D) imaging. Using a Transwell system, we demonstrated that theseK. pneumoniaeisolates translocated across a polarized Caco-2 monolayer. No disruptions of transepithelial electrical resistance and altered distribution of tight junction protein ZO-1 or occludin were observed. Therefore,K. pneumoniaeappeared to penetrate the intestinal epithelium via a transcellular pathway. Using specific inhibitors, we characterized the host signaling pathways involved. Inhibition by cytochalasin D and nocodazole suggested that actin and microtubule cytoskeleton were both important forK. pneumoniaeinvasion. A Rho inhibitor, ML141, LY294002, and an Akt1/2 inhibitor diminishedK. pneumoniaeinvasion in a dose-dependent manner, indicating that Rho family GTPases and phosphatidylinositol 3-kinase (PI3K)/Akt signaling were required. By a mouse model of gastrointestinal colonization,in vivoinvasion ofK. pneumoniaeinto colonic epithelial cells was demonstrated. Our results present evidence to describe a possible mechanism of gastrointestinal translocation forK. pneumoniae. Cell invasion by manipulating host machinery provides a pathway for gut-colonizedK. pneumoniaecells to penetrate the intestinal barrier and access extraintestinal locations to cause disease.