Salmonella Pathogenicity Island 1 Research Articles

Whole-Genome Sequencing Reveals the Population Structure and Genetic Diversity of Salmonella Typhimurium ST34 and ST19 Lineages.

Salmonella Typhimurium is an invasive gastrointestinal pathogen for both humans and animals. To investigate the genetic framework and diversity of S. Typhimurium, a total of 194 S. Typhimurium isolates were collected from patients in a tertiary hospital between 2020 and 2021. Antimicrobial susceptibility testing was used to confirm the resistance phenotype. Whole-genome sequencing and bioinformatics analysis were performed to determine the sequence type, phylogenetic relationships, resistance gene profiles, Salmonella pathogenicity island (SPI) and the diversity of the core and pan genome. The result showed that 57.22% of S. Typhimurium isolates were multidrug resistant and resistance of total isolates to the first-line drug ciprofloxacin was identified in 60.82%. The population structure of S. Typhimurium was categorized into three lineages: ST19 (20.10%, 39/194), ST34-1 (47.42%, 92/194) and ST34-2 (40.65%, 63/194), with the population size exhibiting increasing trends. All lineages harbored variety of fimbrial operons, prophages, SPIs and effectors that contributed to the virulence and long-term infections of S. Typhimurium. Importantly, ST34-1 lineage might potentially be more invasive due to the possession of SPI1-effector gene sopE which was essential for the proliferation, internalization and intracellular presence of S. Typhimurium in hosts. Multiple antimicrobial resistance genes were characteristically distributed across three lineages, especially carbapenem genes only detected in ST34-1&2 lineages. The distinct functional categories of pan genome among three lineages were observed in metabolism, signaling and gene information processing. This study provides a theoretical foundation for the evolved adaptation and genetic diversity of S. Typhimurium ST19 and ST34, among which ST34 lineages with multidrug resistance and potential hypervirulence need to pay more attention to epidemiological surveillance.

Whole-Genome Sequencing Analysis of Antimicrobial Resistance, Virulence Factors, and Genetic Diversity of Salmonella from Wenzhou, China

Salmonella species are important foodborne pathogens worldwide. Salmonella pathogenicity is associated with multiple virulence factors and enhanced antimicrobial resistance. To determine the molecular characteristics and genetic correlations of Salmonella, 24 strains of Salmonella isolated from different sources (raw poultry, human stool, and food) in the Wenzhou area were investigated to determine the distribution of antimicrobial resistance and virulence determinants using whole-genome sequencing (WGS). Aminoglycoside resistance genes were detected in all samples. Over half of the samples found antimicrobial resistance genes (ARGs) and point mutations for several clinically frequently used antibiotic, beta-lactams, tetracyclines, and quinolones. Of these strains, 62.5% were predicted to be multidrug-resistant (MDR). The quinolone-modifying enzyme gene aac(6’)-Ib-cr, detected in five samples (S1–S4 and S10), was located on integrons. The analysis of Salmonella pathogenicity island (SPI) profiles suggests that serotypes with close genetic relationships share the same distribution of virulence factors, revealing a link between genotype and SPI profiles. cgMLST analysis indicated that five isolates S14–S18 were closely related to strains originating from the United Kingdom, suggesting that they may share a common origin. Data from this study may enrich the molecular traceability database for Salmonella and provide a basis for effective public health policies.

Epigallocatechin gallate protects mice from Salmonella enterica ser. Typhimurium infection by modulating bacterial virulence through quorum sensing inhibition.

Salmonella enterica ser. Typhimurium is a common pathogen that poses a considerable public health threat, contributing to severe gastrointestinal diseases and widespread foodborne illnesses. The virulence of S. Typhimurium is regulated by quorum sensing (QS) and the type III secretion system (T3SS). This study investigated the inhibitory effects and anti-QS activity of epigallocatechin gallate (EGCG), which is a bioactive ingredient found in green tea, on the virulence of S. Typhimurium. In vitro bacterial experiments demonstrated that EGCG inhibited the production of autoinducers, biofilm formation, and flagellar activity by downregulating the expression of AI-1, AI-2, Salmonella pathogenicity islands (SPI)-1, SPI-2, and genes related to flagella, fimbriae, and curli fibers. In a mouse model of S. Typhimurium-induced enteritis, EGCG considerably reduced intestinal colonization by S. Typhimurium and alleviated intestinal damage. In conclusion, EGCG protects the intestines of mice infected with S. Typhimurium by inhibiting QS-induced virulence gene expression, demonstrating its potential as a therapeutic agent for controlling S. Typhimurium infections.

Critical role of msgA in invasive capacity and intracellular survivability of Salmonella.

Salmonella enterica serovar Typhimurium is a common foodborne pathogen, it has a complex pathogenic mechanism that involves invasive capacity and intracellular survivability. The virulence of Salmonella is primarily studied through its pathogenicity islands. In contrast, virulence genes located outside the Salmonella pathogenicity islands (SPIs) have received less attention. Macrophage survival gene (MsgA) is positioned at a region independent of the SPIs and conserved in Salmonella. Our research indicates that MsgA is a novel global regulator influencing the metabolic pathways and SPIs. Further research into the function of MsgA will enhance the understanding of Salmonella pathogenesis and promote the application of Salmonella for medical treatment.

Comparison of global transcriptomes for nontyphoidal Salmonella clinical isolates from pediatric patients with and without bacteremia after their interaction with human intestinal epithelial cells in vitro

BackgroundNontyphoidal Salmonella (NTS) outbreaks of invasive diseases are increasing. Whether the genetic diversity of invasive NTS correlates with the clinical characteristics and bacteremia development in NTS infections remains unclear. In this study, we compared the global transcriptomes between bacteremic and nonbacteremic NTS strains after their interaction with human intestinal epithelial cells in vitro. MethodsWe selected clinical isolates obtained from stool and blood samples of patients with or without bacteremia and patients with high and low C-reactive protein (CRP) levels. The bacterial RNA samples were isolated after coculturing with Caco-2 cells for RNA sequencing and subsequent analyses. ResultsCRP is an unreliable predictive maker for NTS bacteremia with a median CRP level of 1.6 mg/dL. Certain Salmonella Pathogenicity Island (SPI)-1 genes (sipC, sipA, sicA, sipD, and sipB), SPI-2 genes (ssaP, ssrA, and ssaS), and six SPI-4 genes (siiA, siiB, siiC, siiD, siiE, and siiF) remained upregulated in the bacteremic blood-derived strains but significantly downregulated in the nonbacteremic strains after their interaction with Caco-2 cells. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis identified that arginine biosynthesis, ascorbate and aldarate metabolism, and phosphotransferase system pathways were activated in bacteremic NTS strains after Caco-2 cell priming. ConclusionCRP levels were not correlated with bacteremia development. Significant regulation of certain SPI genes in bacteremic NTS strains after Caco-2 cell priming; bacteremia development might be influenced by the host immune response and the extent to which specific metabolism pathways in NTS strains can be prevented from invading the bloodstream.

Unusual Case of 20year Male-Resistant Typhoid Fever

A very common infectious disease but still emerging as extensive resistant known as resistant typhoid fever, caused by gram negative Salmonella enterica serovar Typhi(S.Typhi). This bacteria invades human cells by evading host defence system with the help of virulence plasmids and clustered genes called as salmonella pathogenicity islands(SPIs).These factor help bacteria to bind with plasmid mediated antimicrobial resistance gene and enable bacterium to become resistant strain or extensively resistant. After usage of multiple drugs for enteric fever made us to introduce tetracycline as last resort drug.

Genetic Characteristics of Multidrug-Resistant Salmonella Isolated from Poultry Meat in South Korea.

Given the lack of genetic characterization data for multidrug-resistant (MDR) Salmonella in South Korean poultry, we analyzed 53 MDR Salmonella strains from 1232 poultry meat samples (723 chicken, 509 duck) using whole-genome sequencing. Five serotypes were identified: S. Infantis (30/53, 56.6%), S. Enteritidis (11/53, 20.8%), S. Virchow (9/53, 17.0%), S. Agona (2/53, 3.8%), and S. Indiana (1/53, 1.9%). Sequence types (STs) included ST32, ST11, ST16, ST13, and ST17, with three major clusters, each having two subclusters. Eight core genome sequence types (cgSTs) were identified: 225993, 2268, 58360, 150996, 232041, 96964, 117577, and 267045. Salmonella Infantis and S. Enteritidis had two (117577, 267045) and three (225993, 2268, 58360) cgSTs, respectively, whereas S. Virchow showed allelic differences in identical cgSTs. The S. Enteritidis subcluster was classified as chicken or duck. Twenty-eight antimicrobial resistance genes (ARGs), 10 plasmid replicons, 11 Salmonella pathogenicity islands (SPIs), and 230 virulence genes were identified, showing distinct profiles by cluster and subcluster. Salmonella Infantis, the primary MDR Salmonella, carried the IncFIB (pN55391) plasmid, 10-11 ARGs, nine SPIs, and approximately 163 virulence genes. Three major MDR Salmonella serotypes (S. Infantis, S. Enteritidis, and S. Virchow) had specific genetic profiles that can inform epidemiological surveillance.

Modulation of Salmonella virulence by a novel SPI-2 injectisome effector that interacts with the dystrophin-associated protein complex.

In Salmonella enterica, the injectisome machinery encoded by Salmonella pathogenicity island 2 (SPI-2) is conserved among the five subspecies and delivers proteins (effectors) into host cells, which are required for Salmonella virulence. The identification and functional characterization of SPI-2 injectisome effectors advance our understanding of the interplay between Salmonella and its host(s). Using an optimized method for preparing secreted proteins and a clinical isolate of the invasive non-typhoidal Salmonella enterica serovar Enteritidis strain D24359, we identified 22 known SPI-2 injectisome effectors and one new effector-SseM. SseM modulates bacterial growth during murine infection and has a sequence corresponding to a postsynaptic density-95/discs large/zonula occludens-1 (PDZ)-binding motif that is essential for interaction with the PDZ-containing host protein β-2-syntrophin and other components of the dystrophin-associated protein complex (DAPC). To our knowledge, SseM is unique among Salmonella effectors in containing a functional PDZ-binding motif and is the first bacterial protein to target the DAPC.

Genomic insights into antimicrobial resistant Salmonella in internationally traded chicken meat: First baseline findings in the United Arab Emirates

Non-typhoidal Salmonella is among the most prevalent foodborne zoonoses, challenging food safety and One Health worldwide. A dearth of knowledge exists regarding non-typhoidal Salmonella prevalence and genomic features within the United Arab Emirates (UAE), one of the top markets in chicken meat consumption worldwide. In this study, Salmonella was detected in 16 out of 254 (6.30 %, 95 % confidence interval: 3.64 %, 10.03 %) samples of imported frozen chicken carcasses sampled from UAE retails. Among the recovered serotypes, S. Minnesota; ST 548 (10/16) emerged as the most prevalent, trailed by S. Heidelberg; ST 15 (4/16), and then S. Kentucky; ST 198, and ST 152 (2/16). Antimicrobial resistance (AMR) was most prevalent against tetracycline (93.7 %), followed by ampicillin (68.7 %), and extended-spectrum cephalosporins (ceftriaxone and cefoxitin) (56.2 %); with 68.7 % (11/16) of the isolates classified as multidrug resistant (MDR). Whole-genome sequencing (WGS) analysis revealed the existence of 14 AMR genes, among which the blaCMY-2, an AmpC cephalosporinases resistance gene, presented in 10 of the 16 isolates. Among the ten out of the eleven MDR Salmonella isolates, both IncC and Col(pHAD28) plasmid incompatibility types were concurrently featured. The range of virulence genes varied from 149 to 165 genes, with an average of 168 genes per isolate. Except for one isolate, all other isolates possessed type III secretion system (TTSS) related genes known to be encoded by the Salmonella pathogenicity island-1 (SPI-1). This study contributes to our global understanding of Salmonella epidemiology, specifically focusing on the Middle East. The insights gained from this study are significant in shaping import risk analyses aimed at mitigating Salmonella exposure risks through globally traded chicken. The research underscores the value of WGS as a crucial tool for substantiating evidence-based food safety hazard assessment.

Structure classification of the proteins from Salmonella enterica pangenome revealed novel potential pathogenicity islands

Salmonella enterica is a pathogenic bacterium known for causing severe typhoid fever in humans, making it important to study due to its potential health risks and significant impact on public health. This study provides evolutionary classification of proteins from Salmonella enterica pangenome. We classified 17,238 domains from 13,147 proteins from 79,758 Salmonella enterica strains and studied in detail domains of 272 proteins from 14 characterized Salmonella pathogenicity islands (SPIs). Among SPIs-related proteins, 90 proteins function in the secretion machinery. 41% domains of SPI proteins have no previous sequence annotation. By comparing clinical and environmental isolates, we identified 3682 proteins that are overrepresented in clinical group that we consider as potentially pathogenic. Among domains of potentially pathogenic proteins only 50% domains were annotated by sequence methods previously. Moreover, 36% (1330 out of 3682) of potentially pathogenic proteins cannot be classified into Evolutionary Classification of Protein Domains database (ECOD). Among classified domains of potentially pathogenic proteins the most populated homology groups include helix-turn-helix (HTH), Immunoglobulin-related, and P-loop domains-related. Functional analysis revealed overrepresentation of these protein in biological processes related to viral entry into host cell, antibiotic biosynthesis, DNA metabolism and conformation change, and underrepresentation in translational processes. Analysis of the potentially pathogenic proteins indicates that they form 119 clusters or novel potential pathogenicity islands (NPPIs) within the Salmonella genome, suggesting their potential contribution to the bacterium’s virulence. One of the NPPIs revealed significant overrepresentation of potentially pathogenic proteins. Overall, our analysis revealed that identified potentially pathogenic proteins are poorly studied.

Detection of Salmonella Pathogenicity Islands and Antimicrobial-Resistant Genes in Salmonella enterica Serovars Enteritidis and Typhimurium Isolated from Broiler Chickens.

Rapid growth in commercial poultry production is one of the major sources of Salmonella infections that leads to human salmonellosis. The two main Salmonella enterica serovars associated with human salmonellosis are enteritidis and typhimurium. The aim of this study was to determine the prevalence of S. enterica serovars Enteritidis and S. Typhimurium as well as their Salmonella pathogenicity islands (SPI) and antibiotic resistance profiles in broiler chicken feces from slaughterhouses. A total of 480 fecal samples from broiler chickens that were grouped into 96 pooled samples were identified to have Salmonella spp. using the invA gene, whilst the Spy and sdfI genes were used to screen for the presence of S. Enteritidis and S. Typhimurium serovars, respectively, by polymerase chain reaction (PCR) assays. The isolates were also screened for the presence of Salmonella pathogenicity islands (SPIs) using PCR. The disc diffusion assay was performed to determine the antibiotic resistance profiles of the isolates. A total of 36 isolates were confirmed as Salmonella spp. through amplification of the invA gene. Out of 36 confirmed Salmonella spp. a total of 22 isolates were classified as S. Enteritidis (n = 8) and were S. Typhimurium (n = 14) serovars. All (n = 22) S. Enteritidis and S. Typhimurium isolates possessed the hilA (SPI-1), ssrB (SPI-2) and pagC (SPI-11) pathogenicity islands genes. Amongst these serovars, 50% of the isolates (n = 11/22) were resistant to tetracycline and nalidixic acid. Only 22% of the isolates, S. Typhimurium (13.6%) and S. Enteritidis (9.1%) demonstrated resistance against three or more antibiotic classes. The most detected antibiotic resistance genes were tet(K), mcr-1, sulI and strA with 13 (59.1%), 9 (40.9%), 9 (40.9%) and 7 (31.8%), respectively. The findings of this study revealed that S. Typhimurium is the most prevalent serotype detected in chicken feces. To reduce the risk to human health posed by salmonellosis, a stringent public health and food safety policy is required.

Identification of differentially expressed mRNAs as novel predictive biomarkers for gastric cancer diagnosis and prognosis.

Gastric cancer (GC) has a high mortality rate worldwide. Despite significant progress in GC diagnosis and treatment, the prognosis for affected patients still remains unfavorable. To identify important candidate genes related to the development of GC and identify potential pathogenic mechanisms through comprehensive bioinformatics analysis. The Gene Expression Omnibus database was used to obtain the GSE183136 dataset, which includes a total of 135 GC samples. The limma package in R software was employed to identify differentially expressed genes (DEGs). Thereafter, enrichment analyses of Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were performed for the gene modules using the clusterProfile package in R software. The protein-protein interaction (PPI) networks of target genes were constructed using STRING and visualized by Cytoscape software. The common hub genes that emerged in the cohort of DEGs that was retrieved from the GEPIA database were then screened using a Venn Diagram. The expression levels of these overlapping genes in stomach adenocarcinoma samples and non-tumor samples and their association with prognosis in GC patients were also obtained from the GEPIA database and Kaplan-Meier curves. Moreover, real-time quantitative polymerase chain reaction (RT-qPCR) and western blotting were performed to determine the mRNA and protein levels of glutamic-pyruvic transaminase (GPT) in GC and normal immortalized cell lines. In addition, cell viability, cell cycle distribution, migration and invasion were evaluated by cell counting kit-8, flow cytometry and transwell assays. Furthermore, we also conducted a retrospective analysis on 70 GC patients diagnosed and surgically treated in Wenzhou Central Hospital, Dingli Clinical College of Wenzhou Medical University, The Second Affiliated Hospital of Shanghai University between January 2017 to December 2020. The tumor and adjacent normal samples were collected from the patients to determine the potential association between the expression level of GPT and the clinical as well as pathological features of GC patients. We selected 19214 genes from the GSE183136 dataset, among which there were 250 downregulated genes and 401 upregulated genes in the tumor samples of stage III-IV in comparison to those in tumor samples of stage I-II with a P-value < 0.05. In addition, GO and KEGG results revealed that the various upregulated DEGs were mainly enriched in plasma membrane and neuroactive ligand-receptor interaction, whereas the downregulated DEGs were primarily enriched in cytosol and pancreatic secretion, vascular smooth muscle contraction and biosynthesis of the different cofactors. Furthermore, PPI networks were constructed based on the various upregulated and downregulated genes, and there were a total 15 upregulated and 10 downregulated hub genes. After a comprehensive analysis, several hub genes, including runt-related transcription factor 2 (RUNX2), salmonella pathogenicity island 1 (SPI1), lysyl oxidase (LOX), fibrillin 1 (FBN1) and GPT, displayed prognostic values. Interestingly, it was observed that GPT was downregulated in GC cells and its upregulation could suppress the malignant phenotypes of GC cells. Furthermore, the expression level of GPT was found to be associated with age, lymph node metastasis, pathological staging and distant metastasis (P < 0.05). RUNX2, SPI1, LOX, FBN1 and GPT were identified key hub genes in GC by bioinformatics analysis. GPT was significantly associated with the prognosis of GC, and its upregulation can effectively inhibit the proliferative, migrative and invasive capabilities of GC cells.

Antimicrobial resistance, virulence potential and genomic epidemiology of global genomes of the rare Salmonella enterica serovar Orion.

Our aim is to characterize through whole-genome sequencing (WGS) the antimicrobial resistance (AMR) and heavy metal tolerance (HMT) genes content, plasmid presence, virulence potential and genomic diversity of the rare non-typhoid Salmonella enterica serovar Orion (S. Orion) from 19 countries of the African, American, Eastern Mediterranean, European, Southeastern Asia and Western Pacific regions. Totally 324 S. Orion genomes were screened for AMR, HMT and virulence genes, plasmids and Salmonella Pathogenicity Islands (SPIs). Genomic diversity was investigated using Multi-Locus Sequence Typing (MLST) and core-genome MLST (cgMLST). Efflux pump encoding genes mdsA and mdsB were present in all genomes analysed, while quinolone chromosomal point mutations and aminoglycoside, beta-lactam, colistin, lincosamide, macrolide, phenicol, sulphonamide, trimethoprim, tetracycline and disinfectant resistance genes were found in 0.3%-5.9%. A total of 17 genomes (5.2%) from Canada, the United Kingdom, the USA and Tanzania showed a potential multi-drug resistance profile. Gold tolerance genes golS and golT were detected in all genomes analysed, while arsenic, copper, mercury, silver and tellurium tolerance genes were found in 0.3%-35.5%. Col(MGD2) was the most frequently detected plasmid, in 15.4% of the genomes. Virulence genes related to adherence, macrophage induction, magnesium uptake, regulation, serum resistance, stress adaptation, type III secretion systems and six SPIs (1, 2, 3, 4, 5, 9, 12, 13, 14 and C63PI) were detected. ST639 was assigned to 89.2% of the S. Orion genomes, while cgMLST showed core-genome STs and clusters of strains specific by countries. The high virulence factor frequencies, the genomic similarity among some non-clinical and clinical strains circulating worldwide and the presence of a strain carrying a resistance gene against a last resource antimicrobial like colistin, highlight the potential risk of S. Orion strains for public health and food safety and reinforce the importance to not underestimate the potential hazard of rare non-typhoid Salmonella serovars.

Enteric pathogen targeting of the inflammasome pathway

Abstract Pattern recognition receptors-based sensing of microbial products and activities to mount an effective antibacterial defense is an evolutionarily conserved immune strategy. Cytosolic LPS sensing by caspase-11 or -4 and the ensuing noncanonical inflammasome-mediated IL-1 and cell death responses play a central role in the clearance of bacterial pathogens. In response to this selection pressure from the host it is natural that pathogens have developed strategies to actively antagonize or evade inflammasome responses. However, the mechanisms by which bacterial pathogens subvert the noncanonical inflammasome pathway is only beginning to be understood. In this context, this study investigates bacterial modulation of noncanonical inflammasome by utilizing Salmonella entericaserovar Typhimurium as a model enteric pathogen. By screening a library of defined single gene mutants of S. Typhimurium, we found that a mutant that lacks a Salmonella Pathogenicity Island 1 (SPI-1) effector triggers a markedly higher cell death and IL-1 responses in epithelial and professional innate immune cells indicating that this effector protein is a suppressor of inflammasome responses. Further characterization indicated that this effector protein-mediated inhibition of inflammasome responses occurs at the level of gasdermin D, the pyroptotic executioner. Together, this study attributes a novel inflammasome inhibitory function to a Salmonella SPI-1 effector.

Specificities and redundancies in the NEL family of bacterial E3 ubiquitin ligases of Salmonella enterica serovar Typhimurium.

Salmonella enterica serovar Typhimurium expresses two type III secretion systems, T3SS1 and T3SS2, which are encoded in Salmonella pathogenicity island 1 (SPI1) and SPI2, respectively. These are essential virulent factors that secrete more than 40 effectors that are translocated into host animal cells. This study focuses on three of these effectors, SlrP, SspH1, and SspH2, which are members of the NEL family of E3 ubiquitin ligases. We compared their expression, regulation, and translocation patterns, their role in cell invasion and intracellular proliferation, their ability to interact and ubiquitinate specific host partners, and their effect on cytokine secretion. We found that transcription of the three genes encoding these effectors depends on the virulence regulator PhoP. Although the three effectors have the potential to be secreted through T3SS1 and T3SS2, the secretion of SspH1 and SspH2 is largely restricted to T3SS2 due to their expression pattern. We detected a role for these effectors in proliferation inside fibroblasts that is masked by redundancy. The generation of chimeric proteins allowed us to demonstrate that the N-terminal part of these proteins, containing the leucine-rich repeat motifs, confers specificity towards ubiquitination targets. Furthermore, the polyubiquitination patterns generated were different for each effector, with Lys48 linkages being predominant for SspH1 and SspH2. Finally, our experiments support an anti-inflammatory role for SspH1 and SspH2.

Interactions between the AraC/XylS-like transcriptional activator InvF of Salmonella Typhimurium, the RNA polymerase alpha subunit and the chaperone SicA

Salmonella enterica serovar Typhimurium causes gastroenteritis and systemic infections in humans. For this bacterium the expression of a type III secretion system (T3SS) and effector proteins encoded in the Salmonella pathogenicity island-1 (SPI-1), is keystone for the virulence of this bacterium. Expression of these is controlled by a regulatory cascade starting with the transcriptional regulators HilD, HilC and RtsA that induce the expression of HilA, which then activates expression of the regulator InvF, a transcriptional regulator of the AraC/XylS family. InvF needs to interact with the chaperone SicA to activate transcription of SPI-1 genes including sicA, sopB, sptP, sopE, sopE2, and STM1239. InvF very likely acts as a classical activator; however, whether InvF interacts with the RNA polymerase alpha subunit RpoA has not been determined. Results from this study confirm the interaction between InvF with SicA and reveal that both proteins interact with the RNAP alpha subunit. Thus, our study further supports that the InvF/SicA complex acts as a classical activator. Additionally, we showed for the first time an interaction between a chaperone of T3SS effectors (SicA) and the RNAP.

Phosphate (Pi) Transporter PIT1 Induces Pi Starvation in Salmonella-Containing Vacuole in HeLa Cells.

Salmonella enterica serovar Typhimurium (S. Typhimurium), an important foodborne pathogen, causes diarrheal illness and gastrointestinal diseases. S. Typhimurium survives and replicates in phagocytic and non-phagocytic cells for acute or chronic infections. In these cells, S. Typhimurium resides within Salmonella-containing vacuoles (SCVs), in which the phosphate (Pi) concentration is low. S. Typhimurium senses low Pi and expresses virulence factors to modify host cells. However, the mechanism by which host cells reduce the Pi concentration in SCVs is not clear. In this study, we show that through the TLR4-MyD88-NF-κB signaling pathway, S. Typhimurium upregulates PIT1, which in turn transports Pi from SCVs into the cytosol and results in Pi starvation in SCVs. Immunofluorescence and western blotting analysis reveal that after the internalization of S. Typhimurium, PIT1 is located on SCV membranes. Silencing or overexpressing PIT1 inhibits or promotes Pi starvation, Salmonella pathogenicity island-2 (SPI-2) gene expression, and replication in SCVs. The S. Typhimurium ΔmsbB mutant or silenced TLR4-MyD88-NF-κB pathway suppresses the expression of the SPI-2 genes and promotes the fusion of SCVs with lysosomes. Our results illustrate that S. Typhimurium exploits the host innate immune responses as signals to promote intracellular replication, and they provide new insights for the development of broad-spectrum therapeutics to combat bacterial infections.

Whole-genome sequencing of extensively drug-resistant Salmonella enterica serovar Typhi clinical isolates from the Peshawar region of Pakistan

BackgroundTyphoid fever, caused by Salmonella enterica serovar Typhi, is a significant public health concern due to the escalating of antimicrobial resistance (AMR), with limited treatment options for extensively drug-resistant (XDR) S. Typhi strains pose a serious threat to disease management and control. This study aimed to investigate the genomic characteristics, epidemiology and AMR genes of XDR S. Typhi strains from typhoid fever patients in Pakistan. MethodologyWe assessed 200 patients with enteric fever symptoms, confirming 65 S. Typhi cases through culturing and biochemical tests. Subsequent antimicrobial susceptibility testing revealed 40 cases of extensively drug-resistant (XDR) and 25 cases of multi-drug resistance (MDR). Thirteen XDR strains were selected for whole-genome sequencing, to analyze their sequence type, phylogenetics, resistance genes, pathogenicity islands, and plasmid sequences using variety of data analysis resources. Pangenome analysis was conducted for 140 XDR strains, including thirteen in-house and 127 strains reported from other regions of Pakistan, to assess their genetic diversity and functional annotation. ResultsMLST analysis classified all isolates as sequence type 1 (ST-1) with 4.3.1.1. P1 genotype characterization. Prophage and Salmonella Pathogenicity Island (SPI) analysis identified intact prophages and eight SPIs involved in Salmonella's invasion and replication within host cells. Genome data analysis revealed numerous AMR genes including dfrA7, sul1, qnrS1, TEM-1, Cat1, and CTX-M-15, and SNPs associated with antibiotics resistance. IncY, IncQ1, pMAC, and pAbTS2 plasmids, conferring antimicrobial resistance, were detected in a few XDR S. Typhi strains. Phylogenetic analysis inferred a close epidemiological linkage among XDR strains from different regions of Pakistan. Pangenome was noted closed among these strains and functional annotation highlighted genes related to metabolism and pathogenesis. ConclusionThis study revealed a uniform genotypic background among XDR S. Typhi strains in Pakistan, signifying a persistence transmission of a single, highly antibiotic-resistant clone. The closed pan-genome observed underscores limited genetic diversity and highlights the importance of genomic surveillance for combating drug-resistant typhoid infections.

SALMONELLA INFECTION: INTERPLAY BETWEEN THE T3SSS EFFECTORS AND NF-ΚB SIGNALING PATHWAY

Salmonella is an important foodborne pathogen that can evade host immune defense by evolving unique mechanisms. Salmonella manipulate host cell various signaling pathways by delivering specific effectors into target cells to establish infection. The nuclear factor-κB (NF-κB) is an important nuclear transcription factor that regulates the host immune system in Salmonella infection. The Salmonella pathogenicity island 1 (SPI-1) and Salmonella pathogenicity island 2 (SPI-2) encode type III secretion systems (T3SSs), effectors that are associated with the NF-κB signaling pathway through regulate host inflammation response. SPI-1 effectors SipA, SopE, SopE2, and SopB all can activate NF-κB signaling pathway to facilitate Salmonella invasion and intracellular carriage. Studies have shown that T3SS1 and/or T3SS2 effectors such as GtgA, GogA and PipA contain two histidine residues and have metalloprotease activity to control Salmonella replication. These zinc metalloproteases redundantly target the NF-κB subunits p65, RelB, and c-Rel, whereas GogA and GtgA only inhibit NF-κB-dependent gene transcription. The T3SS2 effectors SseK1, SseK2, and SseK3 are death domain-containing proteins with N-linked glycosyltransferase characteristics that can inhibit NF-κB activity by inhibiting IκBα phosphorylation in TNF- α-treated 293ET cells. Among them, SseK1 and SseK3 also suppress Salmonella-induced NF-κB activity in macrophages. SseK3-mediated inhibition of the NF-B signaling pathway is not required for protein 32 containing a tripartite E3-ubiquitin ligase motif. In addition, the SPI-2 T3SS effector SpvD inhibits NF-κB activity by preventing nuclear translocation of p65 through interaction with Exportin-2, but this does not affect IκBα degradation, which ultimately leads to systemic Salmonella growth. However, other effectors SptP, AvrA, IpaJ, SspH1, GtgA, GogA, and SPI-2 encoded SseL, SpvB, SseK1, and GogB all can effectively inhibit NF-κB signaling pathway, and contribute to Salmonella intracellular replication and virulence. In this mini-review, we summarize the special mechanism how NF-κB signaling pathway is regulated by Salmonella T3SSs effectors in the persistent infection of Salmonella, which will further elucidate the pathogenesis of Salmonella.

Deletion of Salmonella pathogenicity islands SPI-1, 2 and 3 induces substantial morphological and metabolic alternation and protective immune potential

The Salmonella Pathogenicity Islands (SPIs) play crucial roles in the progression of Salmonella infection. In this study, we constructed an improved λ Red homologous recombination system to prepare single and triple deletion mutants of three prominent SPIs (SPI-1, 2, and 3), aiming at the impact of deletion on morphology, carbon source metabolism, adhesion and invasion capacity, in vivo colonization, and immune efficacy in chicks. Our examination revealed that the surface of the single deletion mutants (SM6ΔSPI1, ΔSPI2, and ΔSPI3) exhibited a more rugged texture and appeared to be enveloped in a layer of transparent colloid, whereas the morphology of the triple deletion mutant (SM6ΔSPI1&2&3) remained unaltered when compared to the parent strain. The carbon metabolic spectrum of the SPI mutants underwent profound alterations, with a notable and statistically significant modification observed in 30 out of 95 carbon sources, primarily carbohydrates (17 out of 30). Furthermore, the adhesion capacity of the four mutants to Caco-2 cells was significantly reduced when compared to that of the parent strain. Moreover, the invasion capacity of mutants SM6ΔSPI1 and SM6ΔSPI1&2&3 exhibited a substantial decrease, while it was enhanced to varying degrees for SM6ΔSPI3 and SM6ΔSPI2. Importantly, none of the four mutants induced any clinical symptoms in the chicks. However, they did transiently colonize the spleen and liver. Notably, the SM6ΔSPI1&2&3 mutant was rapidly cleared from both the spleen and liver within eight days post-infection and no notable pathological changes were observed in the organs. Additionally, when challenged, the mutants immunized groups displayed a significant increase in antibody levels and alterations in the CD3+CD4+ and CD3+CD8+ subpopulations, and the levels of IL-4 and IFN-γ cytokines in the SM6ΔSPI1&2&3 immunized chicken serum surpassed those of other groups. In summary, the successful construction of the four SPI mutants lays the groundwork for further exploration into the pathogenic (including metabolic) mechanisms of SPIs and the development of safe and effective live attenuated Salmonella vaccines or carriers.