Gallbladder Epithelium as a Niche for Chronic Salmonella Carriage

Abstract

ABSTRACTAlthough typhoid fever has been intensively studied, chronic typhoid carriage still represents a problem for the transmission and persistence of the disease in areas of endemicity. This chronic state is highly associated with the presence of gallstones in the gallbladder of infected carriers upon whichSalmonellacan form robust biofilms. However, we hypothesize that in addition to gallstones, the gallbladder epithelium aids in the establishment/maintenance of chronic carriage. In this work, we present evidence of the role of the gallbladder epithelium in chronic carriage by a mechanism involving invasion, intracellular persistence, and biofilm formation.Salmonellawas able to adhere to and invade polarized gallbladder epithelial cells apically in the absence and presence of bile in aSalmonellapathogenicity island 1 (SPI-1)-dependent manner. Intracellular replication ofSalmonellawas also evident at 12 and 24 h postinvasion. A flowthrough system revealed thatSalmonellais able to adhere to and form extensive bacterial foci on gallbladder epithelial cells as early as 12 h postinoculation.In vivoexperiments using a chronic mouse model of typhoid carriage showed invasion and damage of the gallbladder epithelium and lamina propria up to 2 months afterSalmonellainfection, with an abundant presence of macrophages, a relative absence of neutrophils, and extrusion of infected epithelial cells. Additionally, microcolonies ofSalmonellacells were evident on the surface of the mouse gallbladder epithelia up to 21 days postinfection. These data reveal a second potential mechanism, intracellular persistence and/or bacterial aggregation in/on the gallbladder epithelium with luminal cell extrusion, forSalmonellamaintenance in the gallbladder.