Dormant Intracellular Salmonella enterica Serovar Typhimurium Discriminates among Salmonella Pathogenicity Island 2 Effectors To Persist inside Fibroblasts

Abstract

c Salmonella enterica uses effector proteins delivered by type III secretion systems (TTSS) to colonize eukaryotic cells. Recent in vivo studies have shown that intracellular bacteria activate the TTSS encoded by Salmonella pathogenicity island-2 (SPI-2) to restrain growth inside phagocytes. Growth attenuation is also observed in vivo in bacteria colonizing nonphagocytic stromal cells of the intestinal lamina propria and in cultured fibroblasts. SPI-2 is required for survival of nongrowing bacteria persisting inside fibroblasts, but its induction mode and the effectors involved remain unknown. Here, we show that nongrowing dormant intracellular bacteria use the two-component system OmpR-EnvZ to induce SPI-2 expression and the PhoP-PhoQ system to regulate the time at which induction takes place, 2 h postentry. Dormant bacteria were shown to discriminate the usage of SPI-2 effectors. Among the effectors tested, SseF, SseG, and SseJ were required for survival, while others, such as SifA and SifB, were not. SifA and SifB dispensability correlated with the inability of intracellular bacteria to secrete these effectors even when overexpressed. Conversely, SseJ overproduction resulted in augmented secretion and exacerbated bacterial growth. Dormant bacteria produced other effectors, such as PipB and PipB2, that, unlike what was reported for epithelial cells, did not to traffic outside the phagosomal compartment. Therefore, permissiveness for secreting only a subset of SPI-2 effectors may be instrumental for dormancy. We propose that the S. enterica serovar Typhimurium nonproliferative intracellular lifestyle is sustained by selection of SPI-2 effectors that are produced in tightly defined amounts and delivered to phagosome-confined locations.

Intracellular Salmonella induces aggrephagy of host endomembranes in persistent infections

“…Our previous data show that intracellular S. Typhimurium produces and translocates SPI2 effectors such as SseJ, PipB, and PipB2 at late infection times, 24 hpi. 60 At this late time, the LGP C aggregate has formed and has been digested by aggrephagy (Fig. 3A).…”

“…16,60 The S. Typhimurium-fibroblast infection model is also characterized by the lack of cytotoxicity in the infected cell for long time periods. 41 HeLa human epithelial cells (American Type Culture Collection, CCL-2) were used as control host cell type in which S. Typhimurium proliferates actively.…”

“…60 Coverslips were mounted on glass slides using ProLong (Life Technologies, P36930). For epifluorescence microscopy, we used an inverted Leica DMI 6000B microscope with an automated CTR/7000 HS controller (Leica Microsystems, Wetzlar, Germany) and an Orca-R2 CCD camera (Hamamatsu Photonics, Hamamatsu, Japan), and for optical sectioning, a Leica TCS SP5 spectral laser scanning confocal microscope (Leica Microsystems, Wetzlar, Germany).…”

HilD Induces Expression of Salmonella Pathogenicity Island 2 Genes by Displacing the Global Negative Regulator H-NS from ssrAB

“…SPI-1 genes are required for Salmonella invasion of the intestinal epithelium, leading to enteritis, whereas SPI-2 genes are needed mainly for Salmonella survival and replication within macrophages and consequent establishment of systemic disease (2)(3)(4)(5). SPI-2 genes also induce a nonproliferative intracellular lifestyle by restraining growth inside phagocytes and nonphagocytic cells and contribute to the development of intestinal inflammatory and diarrheal disease, as they enhance Salmonella's transepithelial passage, as well as foster growth inside phagocytes present in the lamina propria (6)(7)(8)(9)(10)(11)(12). In agreement with their pathogenicity roles, SPI-1 genes are expressed when bacteria are in the intestinal lumen or associated with the epithelium or with extruding enterocytes, as well as in a subpopulation of bacteria hyperreplicating in the cytosol of epithelial cells, whereas SPI-2 genes are expressed when bacteria are inside macrophages and also when they are in the intestinal lumen prior to penetrating the intestine, as well as in the lamina propria and in the underlying mucosa (13)(14)(15)(16)(17)(18).…”

Meeting report: Adaptation and communication of bacterial pathogens

“…This session was closed by Francisco Garcıa-del Portillo (CSIC Madrid, Spain) who detailed a suicide strategy involving accumulation of endomembranes to control Salmonella proliferation inside the fibroblast, a cell type in which the pathogen establishes a long lasting persistent infection. 29 His presentation illustrated how an intracellular pathogen can communicate to the host triggering defenses from inside the infected cell to mount "a suicide program. "…”