The transcriptional regulation of the horizontally acquired iron uptake system, yersiniabactin and its contribution to oxidative stress tolerance and pathogenicity of globally emerging salmonella strains.

The bacterial species Salmonella enterica (S. enterica) is a highly diverse pathogen containing more than 2600 distinct serovars, which can infect a wide range of animal and human hosts. Recent global emergence of multidrug resistant strains, from serovars Infantis and Muenchen is associated with acquisition of the epidemic megaplasmid, pESI that augments antimicrobial resistance and pathogenicity. One of the main pESI's virulence factors is the potent iron uptake system, yersiniabactin encoded by fyuA, irp2-irp1-ybtUTE, ybtA, and ybtPQXS gene cluster. Here we show that yersiniabactin, has an underappreciated distribution among different S. enterica serovars and subspecies, integrated in their chromosome or carried by different conjugative plasmids, including pESI. While the genetic organization and the coding sequence of the yersiniabactin genes are generally conserved, a 201-bp insertion sequence upstream to ybtA, was identified in pESI. Despite this insertion, pESI-encoded yersiniabactin is regulated by YbtA and the ancestral Ferric Uptake Regulator (Fur), which binds directly to the ybtA and irp2 promoters. Furthermore, we show that yersiniabactin genes are specifically induced during the mid-late logarithmic growth phase and in response to iron-starvation or hydrogen peroxide. Concurring, yersiniabactin was found to play a previously unknown role in oxidative stress tolerance and to enhance intestinal colonization of S. Infantis in mice. These results indicate that yersiniabactin contributes to Salmonella fitness and pathogenicity in vivo and is likely to play a role in the rapid dissemination of pESI among globally emerging Salmonella lineages.

Persistent Salmonella infections in humans are associated with mutations in the BarA/SirA regulatory pathway.

Several bacterial pathogens, including Salmonella enterica, can cause persistent infections in humans by mechanisms that are poorly understood. By comparing genomes of isolates longitudinally collected from 256 prolonged salmonellosis patients, we identified repeated mutations in global regulators, including the barA/sirA two-component regulatory system, across multiple patients and Salmonella serovars. Comparative RNA-seq analysis revealed that distinct mutations in barA/sirA led to diminished expression of Salmonella pathogenicity islands 1 and 4 genes, which are required for Salmonella invasion and enteritis. Moreover, barA/sirA mutants were attenuated in an acute salmonellosis mouse model and induced weaker transcription of host immune responses. In contrast, in a persistent infection mouse model, these mutants exhibited long-term colonization and prolonged shedding. Taken together, these findings suggest that selection of mutations in global virulence regulators facilitates persistent Salmonella infection in humans, by attenuating Salmonella virulence and inducing a weaker host inflammatory response.

A new Salmonella enterica serovar that was isolated from a wild sparrow presents a distinct genetic, metabolic and virulence profile.

Salmonella enterica is a ubiquitous and clinically-important bacterial pathogen, able to infect and cause different diseases in a wide range of hosts. Here, we report the isolation and characterization of a new S. enterica serovar (13,23:i:-; S. Tirat-Zvi), belonging to the Havana supper-lineage that was isolated from a wild house sparrow (Passer domesticus) in Israel. Whole genome sequencing and complete assembly of its genome indicated a plasmid-free, 4.7 Mb genome that carries the Salmonella pathogenicity islands 1-6, 9, 19 and an integrative and conjugative element (ICE), encoding arsenic resistance genes. Phenotypically, S. Tirat-Zvi isolate TZ282 was motile, readily formed biofilm, more versatile in carbon source utilization than S. Typhimurium and highly tolerant to arsenic, but impaired in host cell invasion. In-vivo infection studies indicated that while S. Tirat-Zvi was able to infect and cause an acute inflammatory enterocolitis in young chicks, it was compromised in mice colonization and did not cause an inflammatory colitis in mice compared to S. Typhimurium. We suggest that these phenotypes reflect the distinctive ecological niche of this new serovar and its evolutionary adaptation to passerine birds, as a permissive host. Moreover, these results further illuminate the genetic, phenotypic and ecological diversity of S. enterica pathovars.

The Effect of Outer Space and Other Environmental Cues on Bacterial Conjugation.

Bacterial conjugation is one of the most abundant horizontal gene transfer (HGT) mechanisms, playing a fundamental role in prokaryote evolution. A better understanding of bacterial conjugation and its cross talk with the environment is needed for a more complete understanding of HGT mechanisms and to fight the dissemination of malicious genes between bacteria. Here, we studied the effect of outer space, microgravity, and additional key environmental cues on transfer (tra) gene expression and conjugation efficiency, using the under studied broad-host range plasmid pN3, as a model. High resolution scanning electron microscopy revealed the morphology of the pN3 conjugative pili and mating pair formation during conjugation. Using a nanosatellite carrying a miniaturized lab, we studied pN3 conjugation in outer space, and used qRT-PCR, Western blotting and mating assays to determine the effect of ground physicochemical parameters on tra gene expression and conjugation. We showed for the first time that bacterial conjugation can occur in outer space and on the ground, under microgravity-simulated conditions. Furthermore, we demonstrated that microgravity, liquid media, elevated temperature, nutrient depletion, high osmolarity and low oxygen significantly reduce pN3 conjugation. Interestingly, under some of these conditions we observed an inverse correlation between tra gene transcription and conjugation frequency and found that induction of at least traK and traL can negatively affect pN3 conjugation frequency in a dose-dependent manner. Collectively, these results uncover pN3 regulation by various environmental cues and highlight the diversity of conjugation systems and the different ways in which they may be regulated in response to abiotic signals. IMPORTANCE Bacterial conjugation is a highly ubiquitous and promiscuous process, by which a donor bacterium transfers a large portion of genetic material to a recipient cell. This mechanism of horizontal gene transfer plays an important role in bacterial evolution and in the ability of bacteria to acquire resistance to antimicrobial drugs and disinfectants. Bacterial conjugation is a complex and energy-consuming process, that is tightly regulated and largely affected by various environmental signals sensed by the bacterial cell. Comprehensive knowledge about bacterial conjugation and the ways it is affected by environmental cues is required to better understand bacterial ecology and evolution and to find new effective ways to counteract the threating dissemination of antibiotic resistance genes between bacterial populations. Moreover, characterizing this process under stress or suboptimal growth conditions such as elevated temperatures, high salinity or in the outer space, may provide insights relevant to future habitat environmental conditions.

The emergence of a multidrug resistant Salmonella Muenchen in Israel is associated with horizontal acquisition of the epidemic pESI plasmid.

OBJECTIVES: Horizontal acquisition of mobile genetic elements is a powerful evolutionary driving force that can profoundly affect pathogens epidemiology and their interactions with the environment and host. In the last decade, the role of the epidemic megaplasmid, pESI was demonstrated in the global emergence of multi-drug resistant (MDR) Salmonella enterica serovar Infantis strains, but it was unknown if this was a one-time phenomenon, or that pESI can drive the emergence of other pathogens. METHODS: Epidemiological, molecular, whole genome sequencing, de-novo assembly, bioinformatics and genetic approaches were used to analyze the emergence of a pESI-positive Salmonella enterica serovar Muenchen strain in Israel. RESULTS: Since 2018, we report the emergence and high prevalence of S. Muenchen in Israel, which consisted at 2020, 40% (1055/2671) of all clinical Salmonella isolates. We show that the emergence of S. Muenchen is dominated by a clonal MDR strain, report its complete assembled genome sequence, and demonstrate that in contrast to preemergent strains, it harbors the epidemic megaplasmid, pESI, which can be self-mobilized into E. coli and other Salmonella serovars. Additionally, we identified bioinformatically highly similar genomes of clinical isolates that were recently collected in South Africa, UK and USA. CONCLUSIONS: This is a second documented case of a pathogen emergence associated with pESI acquisition. Considering the genetic cargo of pESI that enhances resistance, stress tolerance and virulence, and its ability to conjugate into prevalent Salmonella serovars, we provide further support that pESI facilities the emergence and spreading of new Salmonella strains.

Profiling of Secreted Type 3 Secretion System Substrates by Salmonella enterica.

Many of Salmonella enterica virulence-associated phenotypes, including its ability to manipulate various host pathways are mediated by translocation of specific effector proteins via type 3 secretion systems (T3SSs) into the host cell. Culturing Salmonella under a defined set of stimulating conditions in vitro can mimic the physiological signals Salmonella senses during the infection and results in the secretion of these effectors into the growth medium. Here we describe a Salmonella secretion assay to identify and quantify protein substrates secreted by T3SS-1 and demonstrate how this method can be utilized to study the secretion of T3SS-1 effectors and flagellum components in different genetic backgrounds or under varying growth conditions.

In Vivo Tracking of Bacterial Colonization in Different Murine Models Using Bioluminescence: The Example of Salmonella.

Applications of bioluminescence for the in vivo study of pathogenic microorganisms are numerous, ranging from the quantification of virulence gene expression to measuring the effect of antimicrobial molecules on the colonization of tissues and organs by the pathogen. Most studies are performed in mice, but recent works demonstrate that this technique is applicable to larger animals like fish, guinea pigs, ferrets, and chickens. Here, we describe the construction and the utilization of a constitutively luminescent strain of Salmonella Typhimurium to monitor in vivo and ex vivo the colonization of mice in the gastroenteritis, typhoid fever, and asymptomatic carriage models of Salmonella infection.

Intracellular Salmonella Paratyphi A is motile and differs in the expression of flagella-chemotaxis, SPI-1 and carbon utilization pathways in comparison to intracellular S. Typhimurium.

Although Salmonella Typhimurium (STM) and Salmonella Paratyphi A (SPA) belong to the same phylogenetic species, share large portions of their genome and express many common virulence factors, they differ vastly in their host specificity, the immune response they elicit, and the clinical manifestations they cause. In this work, we compared their intracellular transcriptomic architecture and cellular phenotypes during human epithelial cell infection. While transcription induction of many metal transport systems, purines, biotin, PhoPQ and SPI-2 regulons was similar in both intracellular SPA and STM, we identified 234 differentially expressed genes that showed distinct expression patterns in intracellular SPA vs. STM. Surprisingly, clear expression differences were found in SPI-1, motility and chemotaxis, and carbon (mainly citrate, galactonate and ethanolamine) utilization pathways, indicating that these pathways are regulated differently during their intracellular phase. Concurring, on the cellular level, we show that while the majority of STM are non-motile and reside within Salmonella-Containing Vacuoles (SCV), a significant proportion of intracellular SPA cells are motile and compartmentalized in the cytosol. Moreover, we found that the elevated expression of SPI-1 and motility genes by intracellular SPA results in increased invasiveness of SPA, following exit from host cells. These findings demonstrate unexpected flagellum-dependent intracellular motility of a typhoidal Salmonella serovar and intriguing differences in intracellular localization between typhoidal and non-typhoidal salmonellae. We propose that these differences facilitate new cycles of host cell infection by SPA and may contribute to the ability of SPA to disseminate beyond the intestinal lamina propria of the human host during enteric fever.

Meta-analysis defines predominant shared microbial responses in various diseases and a specific inflammatory bowel disease signal.

BACKGROUND: Gut microbial alteration is implicated in inflammatory bowel disease but is noted in other diseases. Systematic comparison to define similarities and specificities is hampered since most studies focus on a single disease. RESULTS: We develop a pipeline to compare between disease cohorts starting from the raw V4 16S amplicon sequence variants. Including 12,838 subjects, from 59 disease cohorts, we demonstrate a predominant shared signature across diseases, indicating a common bacterial response to different diseases. We show that classifiers trained on one disease cohort predict relatively well other diseases due to this shared signal, and hence, caution should be taken when using such classifiers in real-world scenarios, where diseases are intermixed. Based on this common signature across a large array of diseases, we develop a universal dysbiosis index that successfully differentiates between cases and controls across various diseases and can be used for prioritizing fecal donors and samples with lower disease probability. Finally, we identify a set of IBD-specific bacteria, which can direct mechanistic studies and design of IBD-specific microbial interventions. CONCLUSIONS: A robust non-specific general response of the gut microbiome is detected in a large array of diseases. Disease classifiers may confuse between different diseases due to this shared microbial response. Our universal dysbiosis index can be used as a tool to prioritize fecal samples and donors. Finally, the IBD-specific taxa may indicate a more direct association to gut inflammation and disease pathogenesis, and those can be further used as biomarkers and as future targets for interventions.

The ancestral stringent response potentiator, DksA has been adapted throughout Salmonella evolution to orchestrate the expression of metabolic, motility, and virulence pathways.

DksA is a conserved RNA polymerase-binding protein known to play a key role in the stringent response of proteobacteria species, including many gastrointestinal pathogens. Here, we used RNA-sequencing of Escherichia coli, Salmonella bongori and Salmonella enterica serovar Typhimurium, together with phenotypic comparison to study changes in the DksA regulon, during Salmonella evolution. Comparative RNA-sequencing showed that under non-starved conditions, DksA controls the expression of 25%, 15%, and 20% of the E. coli, S. bongori, and S. enterica genes, respectively, indicating that DksA is a pleiotropic regulator, expanding its role beyond the canonical stringent response. We demonstrate that DksA is required for the growth of these three enteric bacteria species in minimal medium and controls the expression of the TCA cycle, glycolysis, pyrimidine biosynthesis, and quorum sensing. Interestingly, at multiple steps during Salmonella evolution, the type I fimbriae and various virulence genes encoded within SPIs 1, 2, 4, 5, and 11 have been transcriptionally integrated under the ancestral DksA regulon. Consequently, we show that DksA is necessary for host cells invasion by S. Typhimurium and S. bongori and for intracellular survival of S. Typhimurium in bone marrow-derived macrophages (BMDM). Moreover, we demonstrate regulatory inversion of the conserved motility-chemotaxis regulon by DksA, which acts as a negative regulator in E. coli, but activates this pathway in S. bongori and S. enterica. Overall, this study demonstrates the regulatory assimilation of multiple horizontally acquired virulence genes under the DksA regulon and provides new insights into the evolution of virulence genes regulation in Salmonella spp.

Pathoadaptation of the passerine-associated Salmonella enterica serovar Typhimurium lineage to the avian host.

Salmonella enterica is a diverse bacterial pathogen and a primary cause of human and animal infections. While many S. enterica serovars present a broad host-specificity, several specialized pathotypes have been adapted to colonize and cause disease in one or limited numbers of host species. The underlying mechanisms defining Salmonella host-specificity are far from understood. Here, we present genetic analysis, phenotypic characterization and virulence profiling of a monophasic S. enterica serovar Typhimurium strain that was isolated from several wild sparrows in Israel. Whole genome sequencing and complete assembly of its genome demonstrate a unique genetic signature that includes the integration of the BTP1 prophage, loss of the virulence plasmid, pSLT and pseudogene accumulation in multiple T3SS-2 effectors (sseJ, steC, gogB, sseK2, and sseK3), catalase (katE), tetrathionate respiration (ttrB) and several adhesion/ colonization factors (lpfD, fimH, bigA, ratB, siiC and siiE) encoded genes. Correspondingly, this strain demonstrates impaired biofilm formation, intolerance to oxidative stress and compromised intracellular replication within non-phagocytic host cells. Moreover, while this strain showed attenuated pathogenicity in the mouse, it was highly virulent and caused an inflammatory disease in an avian host. Overall, our findings demonstrate a unique phenotypic profile and genetic makeup of an overlooked S. Typhimurium sparrow-associated lineage and present distinct genetic signatures that are likely to contribute to its pathoadaptation to passerine birds.

Genome Sequence of an Emerging Salmonella enterica Serovar Infantis and Genomic Comparison with Other S. Infantis Strains.

Salmonella enterica serovar Infantis (S. Infantis) is one of the dominant serovars of the bacterial pathogen S. enterica. In recent years, the number of human infections caused by S. Infantis has been increasing in many countries, and often the emerging population harbors a unique virulence-resistant megaplasmid called plasmid of emerging S. Infantis (pESI). Here, we report the complete gap-free genome sequence of the S. Infantis Israeli emerging clone and compare its chromosome and pESI sequences with other complete S. Infantis genomes. We show a conserved presence of the Salmonella pathogenicity islands 1-6, 9, 11, 12, and CS54 and a common integration of five bacteriophages in the S. Infantis chromosome. In contrast, we found variable presence of additionally three chromosomally integrated phages and eight modular regions in pESI, which contribute to the genetic and phenotypic diversity (including antimicrobial resistance) of this ubiquitous foodborne pathogen.

Emergence of new variants of antibiotic resistance genomic islands among multidrug-resistant Salmonella enterica in poultry.

Non-typhoidal Salmonella enterica (NTS) are diverse and important bacterial pathogens consisting of more than 2600 different serovars, with varying host-specificity. Here, we characterized the poultry-associated serovars in Israel, analysed their resistome and illuminated the molecular mechanisms underlying common multidrug resistance (MDR) patterns. We show that at least four serovars including Infantis, Muenchen, Newport and Virchow present a strong epidemiological association between their temporal trends in poultry and humans. Worrisomely, 60% from all of the poultry isolates tested (n = 188) were multidrug resistant, mediated by chromosomal SNPs and different mobile genetics elements. A novel streptomycin-azithromycin resistance island and previously uncharacterized versions of the mobilized Salmonella genomic island 1 (SGI1) were identified and characterized in S. Blockley and S. Kentucky isolates respectively. Moreover, we demonstrate that the acquisition of SGI1 does not impose fitness cost during growth under nutrient-limited conditions or in the context of Salmonella infection in the mouse model. Overall, our data emphasize the role of the poultry production as a pool of specific epidemic MDR strains and autonomous genetic elements, which confer resistance to heavy metals and medically relevant antibiotics. These are likely to disseminate to humans via the food chain and fuel the increasing global antibiotic resistance crisis.

Std fimbriae-fucose interaction increases Salmonella-induced intestinal inflammation and prolongs colonization.

Expression of ABO and Lewis histo-blood group antigens by the gastrointestinal epithelium is governed by an α-1,2-fucosyltransferase enzyme encoded by the Fut2 gene. Alterations in mucin glycosylation have been associated with susceptibility to various bacterial and viral infections. Salmonella enterica serovar Typhimurium is a food-borne pathogen and a major cause of gastroenteritis. In order to determine the role of Fut2-dependent glycans in Salmonella-triggered intestinal inflammation, Fut2+/+ and Fut2-/- mice were orally infected with S. Typhimurium and bacterial colonization and intestinal inflammation were analyzed. Bacterial load in the intestine of Fut2-/- mice was significantly lower compared to Fut2+/+ mice. Analysis of histopathological changes revealed significantly lower levels of intestinal inflammation in Fut2-/- mice compared to Fut2+/+ mice and measurement of lipocalin-2 level in feces corroborated histopathological findings. Salmonella express fimbriae that assist in adherence of bacteria to host cells thereby facilitating their invasion. The std fimbrial operon of S. Typhimurium encodes the π-class Std fimbriae which bind terminal α(1,2)-fucose residues. An isogenic mutant of S. Typhimurium lacking Std fimbriae colonized Fut2+/+ and Fut2-/- mice to similar levels and resulted in similar intestinal inflammation. In vitro adhesion assays revealed that bacteria possessing Std fimbriae adhered significantly more to fucosylated cell lines or primary epithelial cells in comparison to cells lacking α(1,2)-fucose. Overall, these results indicate that Salmonella-triggered intestinal inflammation and colonization are dependent on Std-fucose interaction.

Differences in the expression of SPI-1 genes pathogenicity and epidemiology between the emerging Salmonella enterica serovar Infantis and the model Salmonella enterica serovar Typhimurium.

BACKGROUND: Salmonella enterica serovar Infantis (S. Infantis) is one of the ubiquitous serovars of the bacterial pathogen S. enterica and recently has been emerging in many countries worldwide. Nonetheless, not much is known about its epidemiology, host adaptation, and virulence. METHODS: Epidemiological and molecular approaches were used together with tissue-culture and mouse models to conduct phenotypic comparison with the model S. enterica serovar Typhimurium. RESULTS: We show that S. Infantis is more frequently associated with infections in infants <2 years old and prone to cause significantly less invasive infections than serovar Typhimurium. Moreover, although S. Infantis adheres better to host cells and highly colonizes mouse intestines soon after infection, it is significantly less invasive and induces much lower inflammation and disease in vivo than S. Typhimurium. These differences were associated with lower expression of Salmonella pathogenicity island (SPI) 1 genes in S. Infantis than in S. Typhimurium. CONCLUSIONS: Our results demonstrate previously unknown differences in the epidemiology, virulence pathway expression, and pathogenicity between two highly abundant Salmonella serovars and suggest that native variation in the expression of the SPI-1 regulon is likely to contribute to epidemiological and virulence variation between genetically similar nontyphoidal Salmonella serovars.

Persistent Infection and Long-Term Carriage of Typhoidal and Nontyphoidal Salmonellae.

The ability of pathogenic bacteria to affect higher organisms and cause disease is one of the most dramatic properties of microorganisms. Some pathogens can establish transient colonization only, but others are capable of infecting their host for many years or even for a lifetime. Long-term infection is called persistence, and this phenotype is fundamental for the biology of important human pathogens, including Helicobacter pylori, Mycobacterium tuberculosis, and Salmonella enterica Both typhoidal and nontyphoidal serovars of the species Salmonella enterica can cause persistent infection in humans; however, as these two Salmonella groups cause clinically distinct diseases, the characteristics of their persistent infections in humans differ significantly. Here, following a general summary of Salmonella pathogenicity, host specificity, epidemiology, and laboratory diagnosis, I review the current knowledge about Salmonella persistence and discuss the relevant epidemiology of persistence (including carrier rate, duration of shedding, and host and pathogen risk factors), the host response to Salmonella persistence, Salmonella genes involved in this lifestyle, as well as genetic and phenotypic changes acquired during prolonged infection within the host. Additionally, I highlight differences between the persistence of typhoidal and nontyphoidal Salmonella strains in humans and summarize the current gaps and limitations in our understanding, diagnosis, and curing of persistent Salmonella infections.

Sink traps as the source of transmission of OXA-48-producing Serratia marcescens in an intensive care unit.

BACKGROUND: Carbapenemase-producing Enterobacteriaceae (CPE) outbreaks are mostly attributed to patient-to-patient transmission via healthcare workers. OBJECTIVE: We describe successful containment of a prolonged OXA-48-producing S. marcescens outbreak after recognizing the sink traps as the source of transmission. METHODS: The Sheba Medical Center intensive care unit (ICU), contains 16 single-bed, semi-closed rooms. Active CPE surveillance includes twice-weekly rectal screening of all patients. A case was defined as a patient detected with OXA-48 CPE >72 hours after admission. A root-cause analysis was used to investigate the outbreak. All samples were inoculated on chrom-agar CRE, and carbapenemase genes were detected using commercial molecular Xpert-Carba-R. Environmental and patient S. marcescens isolates were characterized using PFGE. RESULTS: From January 2016 to May 2017, 32 OXA-48 CPE cases were detected, and 81% of these were S. marcescens. A single clone was the cause of all but the first 2 cases. The common factor in all cases was the use of relatively large amounts of tap water. The outbreak clone was detected in 2 sink outlets and 16 sink traps. In addition to routine strict infection control measures, measures taken to contain the outbreak included (1) various sink decontamination efforts, which eliminated the bacteria from the sink drains only temporarily and (2) educational intervention that engaged the ICU team and lead to high adherence to 'sink-contamination prevention guidelines.' No additional cases were detected for 12 months. CONCLUSIONS: Despite persistence of the outbreak clones in the environmental reservoir for 1 year, the outbreak was rapidly and successfully contained. Addressing sink traps as hidden reservoirs played a major role in the intervention.

Real-Time Reverse Transcription PCR as a Tool to Study Virulence Gene Regulation in Bacterial Pathogens.

Quantitative real-time PCR (qRT-PCR) is a highly sensitive and reliable method for detection and quantification of DNA. When combined with a prior stage of RNA reverse transcription to generate complementary DNA (cDNA), this is a powerful approach to determine and analyze gene transcriptional expression. Real-time quantitative reverse transcription PCR has become the gold standard method in studying genes expression and virulence regulation under various genetic backgrounds (e.g., in the absence of regulators) or environmental conditions. Here we demonstrate the utilization of this approach to study the transcriptional regulation of the conjugation pilus of the Salmonella enterica serovar Infantis virulence plasmid (pESI).

Usage of a Bioluminescence Reporter System to Image Promoter Activity During Host Infection.

Bioluminescence is the process of production and emission of light by a living organism, usually as the by-product of the oxidative enzyme, luciferase. Currently available technology allows for the exploitation of a bioluminescent reporter system to study bacterial gene regulation during rodent infection, in real time, over a large dynamic range. Here we show how this imaging system can be used to study virulence gene regulation during Salmonella enterica infection in the mouse model. To demonstrate this technique we show the ex vivo expression pattern of the gene dksA, encoding a conserved and pleotropic regulator, which plays a key role in Salmonella pathogenicity [1].

lacZ Reporter System as a Tool to Study Virulence Gene Regulation in Bacterial Pathogens.

ß-galactosidase assay has been established as one of the most widely used reporters and can be effectually exploited to study promoter activity of Salmonella and other pathogens under various conditions. This method includes a preliminary stage of fusing the target promoter to a promoter-less lacZ gene encoding for the enzyme ß-galactosidase. Supplementation of the synthetic ONPG substrate results in the accumulation of a chromogenic product proportionally to the activity of the fused promoter. Here we demonstrate the usage of this reporter system to study the regulation of the Salmonella Type three secretion system effector gene sseL in S. Typhimurium [1].