Transcriptome and proteome analysis of Salmonella enterica serovar Typhimurium systemic infection of wild type and immune-deficient mice

Metabolic Proteins Expression Up-Regulated in Blood-Borne Extensively Drug-Resistant Salmonella Typhi Isolates from Pakistan

Background and Objectives: In the undertaken study, proteomics alterations of blood-borne XDR S. Typhi isolated from Pakistan were investigated using mass spectrometry. Materials and Methods: MDR and XDR S. Typhi total protein lysates were fractionated, digested, and processed for nanoflow LC-LTQ-Orbitrap MS analysis. Results: Among the 1267 identified proteins, 37 were differentially regulated, of which 28 were up-regulated, and 9 were down-regulated in XDR S. Typhi as compared to MDR S. Typhi. Based on the functional annotation, proteins found up-regulated are involved mainly in metabolic pathways (ManA, FadB, DacC, GpmA, AphA, PfkB, TalA, FbaB, OtsA, 16504242), the biosynthesis of secondary metabolites (ManA, FadB, GlpB, GpmA, PfkB, TalA, FbaB, OtsA), microbial metabolism in diverse environments (FadB, GpmA, PfkB, NfnB, TalA, FbaB), and ABC transporters (PstS, YbeJ, MglB, RbsB, ArtJ). Proteins found down-regulated are involved mainly in carbon metabolism (FadB, GpmA, PfkB, FalA, FbaB) and the biosynthesis of amino acids (GpmA, PfkB, TalA, FbaB). Most of the identified differential proteins were predicted to be antigenic, and matched with resistome data. Conclusions: A total of 28 proteins were up-regulated, and 9 were down-regulated in XDR S. Typhi. Further characterization of the identified proteins will help in understanding the molecular signaling involved in the emergence of XDR S. Typhi.

The Infectious Dose Shapes Vibrio cholerae Within-Host Dynamics

During infection, the rates of pathogen replication, death, and migration affect disease progression, dissemination, transmission, and resistance evolution. Here, we follow the population dynamics of Vibrio cholerae in a mouse model by labeling individual bacteria with one of >500 unique, fitness-neutral genomic tags. Using the changes in tag frequencies and CFU numbers, we inform a mathematical model that describes the within-host spatiotemporal bacterial dynamics. This allows us to disentangle growth, death, forward, and retrograde migration rates continuously during infection. Our model has robust predictive power across various experimental setups. The population dynamics of V. cholerae shows substantial spatiotemporal heterogeneity in replication, death, and migration. Importantly, we find that the niche available to V. cholerae in the host increases with inoculum size, suggesting cooperative effects during infection. Therefore, it is not enough to consider just the likelihood of exposure (50% infectious dose) but rather the magnitude of exposure to predict outbreaks. IMPORTANCE Determining the rates of bacterial migration, replication, and death during infection is important for understanding how infections progress. Separately measuring these rates is often difficult in systems where multiple processes happen simultaneously. Here, we use next-generation sequencing to measure V. cholerae migration, replication, death, and niche size along the mouse gastrointestinal tract. We show that the small intestine of the mouse is a heterogeneous environment, and the population dynamic characteristics change substantially between adjacent gut sections. Our approach also allows us to characterize the effect of inoculum size on these processes. We find that the niche size in mice increases with the infectious dose, hinting at cooperative effects in larger inocula. The dose-response relationship between inoculum size and final pathogen burden is important for the infected individual and is thought to influence the progression of V. cholerae epidemics.

Iron-Uptake Systems of Chicken-Associated Salmonella Serovars and Their Role in Colonizing the Avian Host

Iron is an essential micronutrient for most bacteria. Salmonella enterica strains, representing human and animal pathogens, have adopted several mechanisms to sequester iron from the environment depending on availability and source. Chickens act as a major reservoir for Salmonella enterica strains which can lead to outbreaks of human salmonellosis. In this review article we summarize the current understanding of the contribution of iron-uptake systems to the virulence of non-typhoidal S. enterica strains in colonizing chickens. We aim to address the gap in knowledge in this field, to help understand and define the interactions between S. enterica and these important hosts, in comparison to mammalian models.

Within-host spatiotemporal dynamic of systemic salmonellosis: Ways to track infection, reaction to vaccination and antimicrobial treatment

During the last two decades our understanding of the complex in vivo host-pathogen interactions has increased due to technical improvements and new research tools. The rapid advancement of molecular biology, flow cytometry and microscopy techniques, combined with mathematical modelling, have empowered in-depth studies of systemic bacterial infections across scales from single molecules, to cells, to organs and systems to reach the whole organism level. By tracking subpopulations of bacteria in vivo using molecular or fluorescent tags, it has been possible to reconstruct the spread of infection within and between organs, allowing unprecedented quantification of the effects of antimicrobial treatment and vaccination. This review illustrates recent advances in the study of heterogeneous traits of the infection process and illustrate approaches to investigate the reciprocal interactions between antimicrobial treatments, bacterial growth/death as well as inter- and intra-organ spread. We also discuss how vaccines impact the in vivo behaviour of bacteria and how these findings can guide vaccine design and rational antimicrobial treatment.

Lactobacillus Protects Against S. Typhimurium-Induced Intestinal Inflammation by Determining the Fate of Epithelial Proliferation and Differentiation

SCOPE

The influence of the intestinal microbiota, such as Lactobacillus, on the intestinal mucosa, particularly intestinal stem cells, remains incompletely understood. In this study, mice and intestinal organoids are used to explore the regulatory effect of Lactobacillus on the proliferation and differentiation of intestinal epithelial cells.

METHODS AND RESULTS

This study demonstrates that S. typhimurium causes intestinal epithelial damage and affected growth of intestinal organoids. S. typhimurium also colonizes the intestine and then causes pathological changes to the intestinal epithelium, intestinal inflammation, and even death. However, L. acidophilus alleviates damage to intestinal organoids, increases the survival ratio of mice infected with S. typhimurium, and reduces tumor necrosis factor-α (TNF-α) secretion. Moreover, L. acidophilus affects the differentiation of epithelial cells through inhibition of the excessive expansion of goblet cells and Paneth cells induced by S. typhimurium to avoid over-exhaustion. Finally, it is also demonstrated that L. acidophilus ameliorates overactivation of Wnt/β-catenin pathway by Salmonella, depending on the contact with toll-like receptor 2 (TLR2), to affect the proliferation of the intestinal epithelium.

CONCLUSIONS

This study demonstrates that L. acidophilus protects the intestinal mucosa against S. typhimurium infection through not only the inhibition of pathogen invasion but also determination of the fate of the intestinal epithelium.

Transcriptional analysis reveals the relativity of acid tolerance and antimicrobial peptide resistance of Salmonella

The objective of this study was to comprehensively identify the target genes induced by acid stimulation in Salmonella, and to clarify the relativity of acid tolerance and antimicrobial peptide resistance. A clinical S. Typhimurium strain, S6, was selected and performed a transcriptome analysis under the acid tolerance response. In total, we found 1461 genes to be differentially expressed, including 721 up-regulated and 740 down-regulated genes. Functional annotation revealed differentially expressed genes to be associated with regulation, metabolism, transport, virulence, and motility. Interestingly, KEGG pathway analysis demonstrated that the induced genes by acid were enriched in cationic antimicrobial peptide resistance, sulfur relay system, ABC transporters, and two-component system pathway. Therein, PhoQ belonging to the two-component system PhoP-PhoQ that promotes virulence by detecting the macrophage phagosome and controls the transcript levels of many genes associated with the resistance to AMPs; MarA, a multiple antibiotic resistance factor; SapA, one of the encoding gene of sapABCDF operon that confers resistance to small cationic peptides of Salmonella; YejB, one of the encoding gene of yejABEF operon that confers resistance to antimicrobial peptides and contributes to the virulence of Salmonella, were all induced by acid stimulation, and could potentially explain that there is a correlation between acid tolerance and AMPs resistance, and finally affects the virulence of intracellular pathogenic bacteria.

The metabolic pathways utilized by Salmonella Typhimurium during infection of host cells

Only relatively recently has research on the metabolism of intracellular bacterial pathogens within their host cells begun to appear in the published literature. This reflects in part the experimental difficulties encountered in separating host metabolic processes from those of the resident pathogen. One of the most genetically tractable and thoroughly studied intracellular bacterial pathogens, Salmonella enterica serovar Typhimurium (S. Typhimurium), has been at the forefront of metabolic studies within eukaryotic host cells. In this review, we offer a synthesis of what has been discovered to date regarding the metabolic adaptation of S. Typhimurium to survival and growth within the infected host. We discuss many studies in the context of techniques used, types of host cells, how host metabolites contribute to intracellular survival and proliferation of the pathogen and how bacterial metabolism affects the virulence and persistence of the pathogen.