YshB is a positive regulator for Salmonella intracellular survival and facilitates the spatio-temporal regulation of bacterial pathogenesis

Salmonella pathogenesis primarily involves invasion of host cells followed by modulation of the intracellular environment for survival and replication. While tremendous progress has been made toward understanding the pathogenesis, the picture is far from complete. In an effort to characterize the role of small RNAs (sRNAs) in Salmonella pathogenesis, we identified a previously undefined small protein YshB as a positive regulator for intracellular bacterial survival and virulence. Essentially, we were able to show YshB was important for survival within macrophages and contributed significantly in mouse virulence. Further, when induced within the bacteria, YshB would lower the invasion efficiency. Notably, yshB expression was found to up-regulate when the bacteria were inside macrophage cells. Moreover, we demonstrate that YshB mediates upregulation of PhoP, a key modulator of Salmonella virulence. We therefore propose a scenario where the induction of YshB mimics the intracellular phase and therefore triggers a down-regulation of the invasion machinery. Interestingly, during the process of elucidating the mechanism of regulation mediated by this small protein, we came across a link between bacterial pathogenesis and fatty acid oxidation pathway. In particular, we found that FadB, an enzyme involved in breakdown of long chain fatty acids was upregulated in the Salmonella cells with induced YshB. FadB was previously implicated to be one of the in vivo induced (ivi) genes, which lead us to speculate that this gene might be important to maintain intracellular survival of Salmonella. We were able to demonstrate that the fadB knockout mutants were indeed compromised in their intracellular life cycle. The upregulation of PhoP and FadB in the YshB induced cells might therefore trigger the spatio-temporal switch from invasion-competent phase of infection to a survival-competent phase. Based on the results we gathered, we therefore postulate a role for this small protein as a molecular liaison to mediate a cross-talk between the invasion competent extracellular and the survival competent intracellular phase of Salmonella

InvS Coordinates Expression of PrgH and FimZ and Is Required for Invasion of Epithelial Cells by Salmonella enterica serovar Typhimurium

ABSTRACT Deep sequencing has revolutionized our understanding of the bacterial RNA world and has facilitated the identification of 280 small RNAs (sRNAs) in Salmonella . Despite the suspicions that sRNAs may play important roles in Salmonella pathogenesis, the functions of most sRNAs remain unknown. To advance our understanding of RNA biology in Salmonella virulence, we searched for sRNAs required for bacterial invasion into nonphagocytic cells. After screening 75 sRNAs, we discovered that the ablation of InvS caused a significant decrease of Salmonella invasion into epithelial cells. A proteomic analysis showed that InvS modulated the levels of several type III secreted Salmonella proteins. The level of PrgH, a type III secretion apparatus protein, was significantly lower in the absence of InvS, consistent with the known roles of PrgH in effector secretion and bacterial invasion. We discovered that InvS modulates fimZ expression and hence flagellar gene expression and motility. We propose that InvS coordinates the increase of PrgH and decrease in FimZ that promote efficient Salmonella invasion into nonphagocytic cells. IMPORTANCE Salmonellosis continues to be the most common foodborne infection reported by the CDC in the United States. Central to Salmonella pathogenesis is the ability to invade nonphagocytic cells and to replicate inside host cells. Invasion genes are known to be regulated by protein transcriptional networks, but little is known about the role played by small RNAs (sRNAs) in this process. We have identified a novel sRNA, InvS, that is involved in Salmonella invasion. Our result will likely provide an opportunity to better understand the fundamental question of how Salmonella regulates invasion gene expression and may inform strategies for therapeutic intervention. </jats:p

Uropathogenic Escherichia coli infection-induced epithelial trained immunity impacts urinary tract disease outcome

Previous urinary tract infections (UTIs) can predispose one to future infections; however, the underlying mechanisms affecting recurrence are poorly understood. We previously found that UTIs in mice cause differential bladder epithelial (urothelial) remodelling, depending on disease outcome, that impacts susceptibility to recurrent UTI. Here we compared urothelial stem cell (USC) lines isolated from mice with a history of either resolved or chronic uropathogenic Escherichia coli (UPEC) infection, elucidating evidence of molecular imprinting that involved epigenetic changes, including differences in chromatin accessibility, DNA methylation and histone modification. Epigenetic marks in USCs from chronically infected mice enhanced caspase-1-mediated cell death upon UPEC infection, promoting bacterial clearance. Increased Ptgs2os2 expression also occurred, potentially contributing to sustained cyclooxygenase-2 expression, bladder inflammation and mucosal wounding-responses associated with severe recurrent cystitis. Thus, UPEC infection acts as an epi-mutagen reprogramming the urothelial epigenome, leading to urothelial-intrinsic remodelling and training of the innate response to subsequent infection