Typhoid fever: pathogenesis and disease

The acidic C-terminal tail of DNA Gyrase of Salmonella enterica serovar Typhi controls DNA relaxation in an acidic environment

The intracellular bacteria, Salmonella Typhi adapts to acidic conditions in the host cell by resetting the chromosomal DNA topology majorly controlled by DNA Gyrase, a Type II topoisomerase. DNA Gyrase forms a heterodimer A2B2 complex, which manages the DNA supercoiling and relaxation in the cell. DNA relaxation forms a part of the regulatory mechanism to activate the transcription of genes required to survive under hostile conditions. Acid-induced stress attenuates the supercoiling activity of the DNA Gyrase, resulting in DNA relaxation. Salmonella DNA becomes relaxed as the bacteria adapt to the acidified intracellular environment. Despite comprehensive studies on DNA Gyrase, the mechanism to control supercoiling activity needs to be better understood. A loss in supercoiling activity in E. coli was observed upon deletion of the non-conserved acidic C-tail of Gyrase A subunit. Salmonella Gyrase also contains an acidic tail at the C-terminus of Gyrase A, where its deletion resulted in reduced supercoiling activity compared to wild-type Gyrase. Interestingly, we also found that wild-type Gyrase compromises supercoiling activity at acidic pH 2-3, thereby causing DNA relaxation. The absence of a C-tail displayed DNA supercoiling to some extent between pH 2-9. Hence, the C-tail of Gyrase A might be one of the controlling factors that cause DNA relaxation in Salmonella at acidic pH conditions. We propose that the presence of the C-tail of GyraseA causes acid-mediated inhibition of the negative supercoiling activity of Gyrase, resulting in relaxed DNA that attracts DNA-binding proteins for controlling the transcriptional response.

Curative anti-typhoid effect of Detarium microcarpum Guill. & Perr. (Leguminosae) hydroethanolic extract root bark based-on in vivo and molecular docking analyses

ETHNOPHARMACOLOGICAL RELEVANCE

Detarium microcarpum is used to treat typhoid fever, a major public health problem, by indigenous population in Africa. Though its preventive activities have been documented, the curative effect is still to be confirmed.

AIM OF THE STUDY

This study aimed at evaluating the curative effects of the hydroethanolic extract of Detarium microcarpum root bark on Salmonella typhimurium-induced typhoid in rat and exploring the in-silico inhibition of some bacterial key enzymes.

STUDY DESIGN

In vitro antioxydant, in vivo antisalmonella of the extract and in silico molecular docking assay on the isolated compounds were carried out to explore the anti-salmonella effects of Detarium microcarpum.

MATERIAL AND METHODS

The in vitro antioxidant properties of the extract were evaluated using DPPH, ABTS and FRAP tests. The anti-salmonella activity of the extract was assessed through feacal sample from Salmonella typhimurium-infected rat cultured in Salmonella-Shigella agar (SS agar) medium. The affinity of isolated compounds (Rhinocerotinoic acid and Microcarposide) from the extract were performed on four key enzymes (Adenylosuccinate lyase, Acetyl coenzyme A synthetase, Thymidine phosphorylase and LuxS-Quorum sensor) using molecular docking simulation to elucidate the molecular level inhibition mechanism.

RESULTS

Crude extract of D. microcarpum root bark showed variable activities on DPPH (RSa50: 6.09 ± 1.04 μg/mL), ABTS (RSa50: 24.46 ± 0.27), and FRAP (RSa50: 23.30 ± 0.23). The extract at all the doses exhibited significant healing effect of infected rats, with the complete clearance. The extract restored hematological, biochemical and histological parameters closed to the normal control. The molecular docking results indicates that rhinocerotinoic acid and microcarposide present more affinity to the LuxS-Quorum sensor and Acetyl coenzyme A synthetase protein as compared to the others.

CONCLUSION

These results demonstrate potent anti-typhoid activities of the hydroethanolic of Detarium microcarpum root bark extract through antioxidant properties and high inhibitory affinity of its compounds on some bacterial key enzymes that justify its use as traditional medicine to typhoid fever.

Salmonella Phage CKT1 Effectively Controls the Vertical Transmission of Salmonella Pullorum in Adult Broiler Breeders

Phage therapy is widely being reconsidered as an alternative to antibiotics for the treatment of multidrug-resistant bacterial infections, including salmonellosis caused by Salmonella. As facultative intracellular parasites, Salmonella could spread by vertical transmission and pose a great threat to both human and animal health; however, whether phage treatment might provide an optional strategy for controlling bacterial vertical infection remains unknown. Herein, we explored the effect of phage therapy on controlling the vertical transmission of Salmonella enterica serovar Gallinarum biovar Pullorum (S. Pullorum), a poultry pathogen that causes economic losses worldwide due to high mortality and morbidity. A Salmonella phage CKT1 with lysis ability against several S. enterica serovars was isolated and showed that it could inhibit the proliferation of S. Pullorum in vitro efficiently. We then evaluated the effect of phage CKT1 on controlling the vertical transmission of S. Pullorum in an adult broiler breeder model. The results demonstrated that phage CKT1 significantly alleviated hepatic injury and decreased bacterial load in the liver, spleen, heart, ovary, and oviduct of hens, implying that phage CKT1 played an active role in the elimination of Salmonella colonization in adult chickens. Additionally, phage CKT1 enabled a reduction in the Salmonella-specific IgG level in the serum of infected chickens. More importantly, the decrease in the S. Pullorum load on eggshells and in liquid whole eggs revealed that phage CKT1 effectively controlled the vertical transmission of S. Pullorum from hens to laid eggs, indicating the potential ability of phages to control bacterial vertical transmission.

Asiatic Acid Attenuates Inflammation Induced by Salmonella via Upregulating LncRNA TVX1 in Microglia

Salmonella typhimurium (S.T) induces damage to the central nervous system; however, the role of Asiatic acid (AA) in this is still unknown. Microglia play a role as macrophages to recognize the invaded pathogenic microbes in the brain. The aim of this study was to investigate the protective effect and mechanism of AA on the central nervous system through an in vitro model of S.T infection in microglia. We pre-treated microglia with AA before S.T infection and explored the anti-infection mechanism of AA by sequencing, quantitative reverse transcription PCR (RT-qPCR), and Western blotting. Long non-coding RNA (lncRNA) sequencing demonstrated that inflammation is a major factor in S.T infection of microglia. RT-qPCR data demonstrated that AA inhibited S.T-induced increases in the mRNA levels of the pro-inflammatory factors interleukin (IL)-1β, IL-6, and IL-18. Western blotting demonstrated that AA inhibited S.T-induced activation of the nuclear factor (NF)-κB pathway and activation of the NLR family, pyrin domain-containing 3 (NLRP3) inflammasome. Expression of the lncRNA TVX1 in microglia was decreased by S.T infection and increased by pretreatment with AA. Inhibition of TVX1 expression reversed the anti-inflammatory effect of AA, and overexpression of TVX1 in microglia suppressed S.T-induced inflammation. In conclusion, AA attenuated S.T-induced microglial inflammation by upregulating the expression of the lncRNA TVX1.

Mathematical Models for Typhoid Disease Transmission: A Systematic Literature Review

Explaining all published articles on the typhoid disease transmission model was carried out. It has been conducted to understand how Salmonella is transmitted among humans and vectors with variation interventions to control the spread of the typhoid disease. Specific objectives were to (1) identify the model developed, (2) describe the studies, and (3) identify the interventions of the model. It systemically searched and reviewed Dimension, Scopus, and ScienceDirect databases from 2013 through to 2022 for articles that studied the spread of typhoid fever through a compartmental mathematical model. This study obtained 111 unique articles from three databases, resulting in 23 articles corresponding to the created terms. All the articles were elaborated on to identify their identities for more explanation. Various interventions were considered in the model of each article, are identified, and then summarized to find out the opportunities for model development in future works. The whole article’s content was identified and outlined regarding how mathematics plays a role in model analysis and study of typhoid disease spread with various interventions. The study of mathematical modeling for typhoid disease transmission can be developed on analysis and creating the model with direct and indirect interventions to the human population for further work.

Hematology Parameter Based on Tubex TF® Color Scale Result in Typhoid Fever Patients

BACKGROUND: Infection with Salmonella enterica subspecies serovar Typhi and Paratyphi A, B, and C causes typhoid and paratyphoid fever. This is a major source of mortality and morbidity, especially in youngsters. Typhoid fever frequently causes non-specific symptoms. Symptoms that appear obstructively are comparable to those seen in other infectious illnesses and have similar clinical manifestations. Complications can be avoided with early detection and treatment. AIM: This study will look at the hematology parameter profile to determine whether there are any hematological differences between patients with high and low antibodies. METHODS: The research was conducted in Bengkulu, Indonesia, in June 2020 until July 2021. Subject collection was done according to inclusion and exclusion criteria. Subjects have given informed consent. The research included a total of 39 subject patients. Demographic data were collected using a questionnaire and 3 mL of blood was taken. Blood was examined for Tubex TF® and hematological examination. Statistical analysis used independent t-test and performed with SPSS. RESULTS: The research included a total of 39 subject patients. Most were male and most were aged 21–25 years. The most common symptom felt by the subject was gastrointestinal complaints. The analysis was carried out based on the color scale value of the Tubex TF® which was divided into two groups, 4 color scale groups and 6 color scale groups. Hematological parameters of hemoglobin, hematocrit, WBC, platelets, monocytes, lymphocytes, and neutrophils showed no significant difference. However, color scale group 6 showed lower value than 4 color scale group. CONCLUSION: Hematological indicators in typhoid fever were not substantially changed in Tubex TF®-positive typhoid fever patients. Clinicians can offer the same therapy in instances with typhoid fever, despite having differing positive Tubex TF® scores.

Molecular Methods for Pathogenic Bacteria Detection and Recent Advances in Wastewater Analysis

With increasing concerns about public health and the development of molecular techniques, new detection tools and the combination of existing approaches have increased the abilities of pathogenic bacteria monitoring by exploring new biomarkers, increasing the sensitivity and accuracy of detection, quantification, and analyzing various genes such as functional genes and antimicrobial resistance genes (ARG). Molecular methods are gradually emerging as the most popular detection approach for pathogens, in addition to the conventional culture-based plate enumeration methods. The analysis of pathogens in wastewater and the back-estimation of infections in the community, also known as wastewater-based epidemiology (WBE), is an emerging methodology and has a great potential to supplement current surveillance systems for the monitoring of infectious diseases and the early warning of outbreaks. However, as a complex matrix, wastewater largely challenges the analytical performance of molecular methods. This review synthesized the literature of typical pathogenic bacteria in wastewater, types of biomarkers, molecular methods for bacterial analysis, and their recent advances in wastewater analysis. The advantages and limitation of these molecular methods were evaluated, and their prospects in WBE were discussed to provide insight for future development.

Yin and Yang of Biofilm Formation and Cyclic di-GMP Signaling of the Gastrointestinal Pathogen Salmonella enterica Serovar Typhimurium

Within the last 60 years, microbiological research has challenged many dogmas such as bacteria being unicellular microorganisms directed by nutrient sources; these investigations produced new dogmas such as cyclic diguanylate monophosphate (cyclic di-GMP) second messenger signaling as a ubiquitous regulator of the fundamental sessility/motility lifestyle switch on the single-cell level. Successive investigations have not yet challenged this view; however, the complexity of cyclic di-GMP as an intracellular bacterial signal, and, less explored, as an extracellular signaling molecule in combination with the conformational flexibility of the molecule, provides endless opportunities for cross-kingdom interactions. Cyclic di-GMP-directed microbial biofilms commonly stimulate the immune system on a lower level, whereas host-sensed cyclic di-GMP broadly stimulates the innate and adaptive immune responses. Furthermore, while the intracellular second messenger cyclic di-GMP signaling promotes bacterial biofilm formation and chronic infections, oppositely, Salmonella Typhimurium cellulose biofilm inside immune cells is not endorsed. These observations only touch on the complexity of the interaction of biofilm microbial cells with its host. In this review, we describe the Yin and Yang interactive concepts of biofilm formation and cyclic di-GMP signaling using S. Typhimurium as an example.

Salmonella Typhimurium and inflammation: a pathogen-centric affair

Microbial infections are controlled by host inflammatory responses that are initiated by innate immune receptors after recognition of conserved microbial products. As inflammation can also lead to disease, tissues that are exposed to microbial products such as the intestinal epithelium are subject to stringent regulatory mechanisms to prevent indiscriminate signalling through innate immune receptors. The enteric pathogen Salmonella enterica subsp. enterica serovar Typhimurium, which requires intestinal inflammation to sustain its replication in the intestinal tract, uses effector proteins of its type III secretion systems to trigger an inflammatory response without the engagement of innate immune receptors. Furthermore, S. Typhimurium uses a different set of effectors to restrict the inflammatory response to preserve host homeostasis. The S. Typhimurium-host interface is a remarkable example of the unique balance that emerges from the co-evolution of a pathogen and its host.

Revisiting Persistent Salmonella Infection and the Carrier State: What Do We Know?

One characteristic of the few Salmonella enterica serovars that produce typhoid-like infections is that disease-free persistent infection can occur for months or years in a small number of individuals post-convalescence. The bacteria continue to be shed intermittently which is a key component of the epidemiology of these infections. Persistent chronic infection occurs despite high levels of circulating specific IgG. We have reviewed the information on the basis for persistence in S. Typhi, S. Dublin, S. Gallinarum, S. Pullorum, S. Abortusovis and also S. Typhimurium in mice as a model of persistence. Persistence appears to occur in macrophages in the spleen and liver with shedding either from the gall bladder and gut or the reproductive tract. The involvement of host genetic background in defining persistence is clear from studies with the mouse but less so with human and poultry infections. There is increasing evidence that the organisms (i) modulate the host response away from the typical Th1-type response normally associated with immune clearance of an acute infection to Th2-type or an anti-inflammatory response, and that (ii) the bacteria modulate transformation of macrophage from M1 to M2 type. The bacterial factors involved in this are not yet fully understood. There are early indications that it might be possible to remodulate the response back towards a Th1 response by using cytokine therapy.

Association of quorum sensing and biofilm formation with Salmonella virulence: story beyond gathering and cross-talk

Enteric fever (typhoid and paratyphoid fever) is a public health concern which contributes to mortality and morbidity all around the globe. It is caused mainly due to ingestion of contaminated food and water with a gram negative, rod-shaped, flagellated bacterium known as Salmonella enterica serotype typhi (typhoid fever) or paratyphi (paratyphoid fever). Clinical problems associated with Salmonellosis are mainly bacteraemia, gastroenteritis and enteric fever. The bacteria undergo various mechanisms to escape itself from immune reaction of the host, modulating immune response at the site of infection leading to virulence factor production and anti-microbial resistance. Biofilm is one of the adaptation mechanisms through which Salmonella survives in unfavourable conditions and thus is considered as a major threat to public health. Another property of the bacteria is "Quorum Sensing", which is a cell-cell communication and most of the pathogenic bacteria use it to coordinate the production of several virulence factors and other behaviours such as swarming and biofilm formation. Earlier, quorum sensing was believed to be just a medium for communication but, later on, its role in virulence has been studied. However, there are negligible information relating to interaction between quorum sensing and biofilm formation and how these events play crucial role in Salmonella pathogenesis. The review is a summary of updated information regarding how Salmonella uses these properties to spread more and survive better, making a challenge for clinicians and public health experts. Therefore, this review would help bring an insight regarding how biofilm formation and quorum sensing are inter-related and their role in pathogenesis and virulence of Salmonella.

A Novel Approach against Salmonella: A Review of Polymeric Nanoparticle Vaccines for Broilers and Layers

This work discusses the present-day limitations of current commercial Salmonella vaccines for broilers and layers and explores a novel approach towards poultry vaccination using biodegradable nanoparticle vaccines against Salmonella. With the increasing global population and poultry production and consumption, Salmonella is a potential health risk for humans. The oral administration of killed or inactivated vaccines would provide a better alternative to the currently commercially available Salmonella vaccines for poultry. However, there are currently no commercial oral killed-vaccines against Salmonella for use in broilers or layers. There is a need for novel and effective interventions in the poultry industry. Polymeric nanoparticles could give way to an effective mass-administered mucosal vaccination method for Salmonella. The scope of this work is limited to polymeric nanoparticles against Salmonella for use in broilers and layers. This review is based on the information available at the time of the investigation.

Chitosan-adjuvanted Salmonella subunit nanoparticle vaccine for poultry delivered through drinking water and feed

Poor induction of mucosal immunity in the intestines by current Salmonella vaccines is a challenge to the poultry industry. We prepared and tested an oral deliverable Salmonella subunit vaccine containing immunogenic outer membrane proteins (OMPs) and flagellin (F) protein loaded and F-protein surface coated chitosan nanoparticles (CS NPs) (OMPs-F-CS NPs). The OMPs-F-CS NPs had mean particle size distribution of 514 nm, high positive charge and spherical in shape. In vitro and in vivo studies revealed the F-protein surface coated CS NPs were specifically targeted to chicken immune cells. The OMPs-F-CS NPs treatment of chicken immune cells upregulated TLRs, and Th1 and Th2 cytokines mRNA expression. Oral delivery of OMPs-F-CS NPs in birds enhanced the specific systemic IgY and mucosal IgA antibodies responses as well as reduced the challenge Salmonella load in the intestines. Thus, user friendly oral deliverable chitosan-based Salmonella vaccine for poultry is a viable alternative to current vaccines.

Endocytosis and the internalization of pathogenic organisms: focus on phosphoinositides

Despite their comparatively low abundance in biological membranes, phosphoinositides are key to the regulation of a diverse array of signaling pathways and direct membrane traffic. The role of phosphoinositides in the initiation and progression of endocytic pathways has been studied in considerable depth. Recent advances have revealed that distinct phosphoinositide species feature prominently in clathrin-dependent and -independent endocytosis as well as in phagocytosis and macropinocytosis. Moreover, a variety of intracellular and cell-associated pathogens have developed strategies to commandeer host cell phosphoinositide metabolism to gain entry and/or metabolic advantage, thereby promoting their survival and proliferation. Here, we briefly survey the current knowledge on the involvement of phosphoinositides in endocytosis, phagocytosis, and macropinocytosis and highlight several examples of molecular mimicry employed by pathogens to either “hitch a ride” on endocytic pathways endogenous to the host or create an entry path of their own.

Functional analysis of Salmonella Typhi adaptation to survival in water

Contaminated water is a major risk factor associated with the transmission of Salmonella enterica serovar Typhi (S. Typhi), the aetiological agent of human typhoid. However, little is known about how this pathogen adapts to living in the aqueous environment. We used transcriptome analysis (RNA‐seq) and transposon mutagenesis (TraDIS) to characterize these adaptive changes and identify multiple genes that contribute to survival. Over half of the genes in the S. Typhi genome altered expression level within the first 24 h following transfer from broth culture to water, although relatively few did so in the first 30 min. Genes linked to central metabolism, stress associated with arrested proton motive force and respiratory chain factors changed expression levels. Additionally, motility and chemotaxis genes increased expression, consistent with a scavenging lifestyle. The viaB‐associated gene tviC encoding a glcNAc epimerase that is required for Vi polysaccharide biosynthesis was, along with several other genes, shown to contribute to survival in water. Thus, we define regulatory adaptation operating in S. Typhi that facilitates survival in water.

Detection of Salmonella pathogenicity island and Salmonella plasmid virulence genes in Salmonella Enteritidis originated from layer and broiler farms in Java Island

OBJECTIVE

The incidence of salmonellosis in humans and animals is still high due to the occurrence of virulence factors in Salmonella enterica which play a role in the process of infection in the host and the spread of disease and most of the S. enterica can infect humans and animals. The present study was aimed to identify Salmonella Enteritidis and detect virulence genes related to Salmonella pathogenicity islands (SPIs) and Salmonella plasmid virulence (Spv).

MATERIALS AND METHODS

A total of 27 S. Enteritidis archive isolates belonging to the National Veterinary Drug Assay Laboratory (NVDAL) were used in this study. The bacteria were collected in 2016 and 2017 from samples of the cloaca and fecal swabs from layer and broiler farms in five provinces of Java Island. Isolates were cultured in specific media, biochemical tests and Gram staining. Detection of S. Enteritidis and virulence genes was done by polymerase chain reaction (PCR) method.

RESULTS

Identification of serovar showed 100% (27/27) isolates were positive for the sdfI gene (304 bp). The result confirmed that all strains were S. Enteritidis. PCR based detection of virulence genes showed that 100% of isolates had virulence genes in SPI-1 to SPI-5, namely, invA, ssaQ, mgtC, spi4D, and pipA genes. All the isolates (27/27) were also positive to spvB gene-based PCR.

CONCLUSION

All the isolates of S. Enteritidis in this study carry virulence genes related to SPI-1 to SPI-5 and plasmid virulence. The existence of virulent genes indicates that the S. Enteritidis strain examined in this study is highly virulent and poses a potential threat of worse disease outcome in humans and animals.

Why Is Eradicating Typhoid Fever So Challenging: Implications for Vaccine and Therapeutic Design

Salmonella enterica serovar Typhi (S. Typhi) and S. Paratyphi, namely typhoidal Salmonellae, are the cause of (para) typhoid fever, which is a devastating systemic infectious disease in humans. In addition, the spread of multidrug-resistant (MDR) and extensively drug-resistant (XDR) S. Typhi in many low and middle-income countries poses a significant risk to human health. While currently available typhoid vaccines and therapeutics are efficacious, they have some limitations. One important limitation is the lack of controlling individuals who chronically carry S. Typhi. However, due to the strict host specificity of S. Typhi to humans, S. Typhi research is hampered. As a result, our understanding of S. Typhi pathogenesis is incomplete, thereby delaying the development and improvement of prevention and treatment strategies. Nonetheless, to better combat and contain S. Typhi, it is vital to develop a vaccine and therapy for controlling both acutely and chronically infected individuals. This review discusses how scientists are trying to combat typhoid fever, why it is so challenging to do so, which approaches show promise, and what we know about the pathogenesis of S. Typhi chronic infection.

Model of Persistent Salmonella Infection: Salmonella enterica Serovar Pullorum Modulates the Immune Response of the Chicken from a Th17-Type Response towards a Th2-Type Response

Salmonella enterica infection affects a wide range of animals and humans, and a small number of serovars cause typhoid-like infections, one characteristic of which is persistent infection in convalescents. Avian-specific S. enterica serovar Pullorum produces systemic disease in young chickens, which is followed by a carrier state in convalescent birds, leading to infection of the ovary at sexual maturity and vertical transmission. However, the immunological basis of persistent infection remains unclear. S. enterica serovar Enteritidis is taxonomically closely related but does not show this characteristic. Differences in the immune responses between S Pullorum and S Enteritidis were compared by using Salmonella-infected chicken monocyte-derived macrophages (chMDMs) and CD4⁺ T lymphocytes that had been cocultured with infected chMDMs or chicken splenocytes in vitro and also in 2-day-old chickens in vivo In comparison with S Enteritidis, S Pullorum-infected chMDMs showed reduced mRNA expression levels of interleukin-12α (IL-12α) and IL-18 and stimulated the proliferation of Th2 lymphocytes, with reduced expression of gamma interferon (IFN-γ) and IL-17 and increased expression levels of IL-4 and IL-13 There was little evidence of clonal anergy or immune suppression induced by S Pullorum in vitro. S Pullorum also increased the levels of expression of IL-4 and decreased the levels of IFN-γ in the spleen and cecal tonsil of infected birds. This suggests that S Pullorum is able to modulate host immunity from a dominant IFN-γ-producing Th17 response toward a Th2 response, which may promote persistent infection in chickens. S Pullorum in chickens is presented as a good model of the typhoid group to study persistent infection.

The role of lipids in host-pathogen interactions

Innate immunity relies on the effective recognition and elimination of pathogenic microorganisms. This entails sequestration of pathogens into phagosomes that promptly acquire microbicidal and degradative properties. This complex series of events, which involve cytoskeletal reorganization, membrane remodeling and the activation of multiple enzymes, is orchestrated by lipid signaling. To overcome this immune response, intracellular pathogens acquired mechanisms to subvert phosphoinositide-mediated signaling and use host lipids, notably cholesterol, as nutrients. We present brief overviews of the role of phosphoinositides in phagosome formation and maturation as well as of cholesterol handling by host cells, and selected Salmonella, Shigella, Chlamydia and Mycobacterium tuberculosis to exemplify the mechanisms whereby intracellular pathogens co-opt lipid metabolism in host cells. © 2018 IUBMB Life, 70(5):384-392, 2018.

Bi-valent polysaccharides of Vi capsular and O9 O-antigen in attenuated Salmonella Typhimurium induce strong immune responses against these two antigens

Salmonella Typhi is the causative agent of typhoid fever in humans, responsible for approximately 21 million infections and 222,000 deaths globally each year. The current licensed vaccines provide moderate protection to recipients aged >2 years. Prior work on typhoid vaccines has focused on injectable Vi capsular polysaccharide or Vi–protein conjugates and live, oral attenuated S. Typhi vaccines to induce humoral anti-Vi antibodies, while the value and importance of anti-O9 antibodies is less well established. In this study, we constructed a S. Typhimurium strain that synthesizes Vi capsular antigen in vivo and produces the immunodominant O9-antigen polysaccharide instead of its native O4-antigen. The live recombinant attenuated S. Typhimurium mutants were effective in stimulating anti-Vi and anti-O9 antibodies in a mouse model, and the surface Vi capsular expression did not affect the immune responses against the O9 O-antigen polysaccharide. Moreover, the resulting anti-Vi and anti-O9 antibodies were effective at killing S. Typhi and other Salmonella spp. expressing Vi or O9 antigen polysaccharides and provided efficient protection against lethal challenge by S. Typhimurium and S. Enteritidis. Our work highlights the strategy of developing live attenuated S. Typhimurium vaccines to prevent typhoid fever by targeting the both Vi capsular and O9 O-polysaccharide antigens simultaneously.

An attenuated strain of modified Salmonella Typhimurium bacteria could answer calls for a more effective typhoid fever vaccine. Current vaccines against typhoid-causing Salmonella Typhi are only moderately effective and potentially ineffective in children under 5 years. Qingke Kong and Roy Curtiss, leading a team of US and Chinese researchers, developed an attenuated version of the less-pathogenic S. Typhimurium that, when orally dosed in mice, expresses bacterial sugar-chain molecules known to elicit a strong immune response. In an in vitro assay, the antibodies produced by the mice in response to these molecules killed S. Typhi and related Salmonella bacteria with similar surface molecules, indicating a potential cross-protective ability. Further research would reveal whether this two-pronged live vaccine has the potential to protect in vivo, in live animals and in humans.

The Typhi colonization factor (Tcf) is encoded by multiple non-typhoidal Salmonella serovars but exhibits a varying expression profile and interchanging contribution to intestinal colonization

Salmonella enterica serovars Typhi and Paratyphi A are human-restricted pathogens and the leading causative agents of enteric fever. The Typhi colonization factor (Tcf) is a chaperone-usher fimbria, thought to play a role in the host-specificity of typhoidal serovars. Here we show that the tcf cluster (tcfABCD tinR tioA) is present in at least 25 non-typhoidal Salmonella (NTS) serovars and demonstrate its native expression in clinically-important serovars including Schwarzengrund, 9,12:l,v:-, Choleraesuis, Bredeney, Heidelberg, Montevideo, Virchow and Infantis. Although the genetic organization of the tcf cluster is well conserved, the N-terminal half of the fimbrial adhesin, TcfD is highly diverse, suggesting different binding properties of distinct tcfD variants. Comparison of tcfA expression in typhoidal and NTS serovars demonstrated unexpected differences in its expression profiles, with the highest transcription levels in S. Typhi, S. Choleraesuis and S. Infantis. In the latter, tcf is induced in rich broth and under microaerobic conditions, characterizing the intestines of warm blooded animals. Furthermore, Tcf is negatively regulated by the ancestral leucine-responsive transcriptional regulator (Lrp). Using the colitis mouse model, we demonstrate that during mice infection tcfA is expressed at higher levels by S. Infantis than S. Schwarzengrund or S. Heidelberg. Moreover, while Tcf is dispensable for S. Schwarzengrund and S. Heidelberg mouse colonization, Tcf is involved in cecum and colon colonization by S. Infantis. Taken together, our results establish that Tcf is broadly encoded by multiple NTS serovars, but presents variable expression profiles and contributes differently to their virulence.

Receptor-Mediated Sorting of Typhoid Toxin during Its Export from Salmonella Typhi-Infected Cells

Typhoid toxin is an essential virulence factor of Salmonella Typhi, the cause of typhoid fever. Typhoid toxin is secreted into the lumen of Salmonella-containing vacuole (SCV), after which it is packaged into vesicle carrier intermediates and released extracellularly through incompletely understood mechanisms. Following export, the toxin targets cells by interacting with human-specific Neu5Ac-terminated glycan receptors. We show that typhoid toxin is sorted from the SCV into vesicle carrier intermediates via interactions of its B subunit, PltB, with specific lumenal sialylated glycan packaging receptors. Cells deficient in N-glycosylation or the synthesis of specific gangliosides or displaying Neu5Gc-terminated, as opposed to Neu5Ac-terminated, glycans do not support typhoid toxin export. Additionally, typhoid toxin packaging requires the specific SCV environment, as toxin produced by an S. Typhi mutant with impaired trafficking is not properly sorted into vesicles. These results reveal how the exotoxin of an intracellular pathogen engages host pathways for packaging and release.

The plasmid-encoded Ipf and Klf fimbriae display different expression and varying roles in the virulence of Salmonella enterica serovar Infantis in mouse vs. avian hosts

Salmonella enterica serovar Infantis is one of the prevalent Salmonella serovars worldwide. Different emergent clones of S. Infantis were shown to acquire the pESI virulence-resistance megaplasmid affecting its ecology and pathogenicity. Here, we studied two previously uncharacterized pESI-encoded chaperone-usher fimbriae, named Ipf and Klf. While Ipf homologs are rare and were found only in S. enterica subspecies diarizonae and subspecies VII, Klf is related to the known K88-Fae fimbria and klf clusters were identified in seven S. enterica subspecies I serovars, harboring interchanging alleles of the fimbria major subunit, KlfG. Regulation studies showed that the klf genes expression is negatively and positively controlled by the pESI-encoded regulators KlfL and KlfB, respectively, and are activated by the ancestral leucine-responsive regulator (Lrp). ipf genes are negatively regulated by Fur and activated by OmpR. Furthermore, induced expression of both klf and ipf clusters occurs under microaerobic conditions and at 41°C compared to 37°C, in-vitro. Consistent with these results, we demonstrate higher expression of ipf and klf in chicks compared to mice, characterized by physiological temperature of 41.2°C and 37°C, respectively. Interestingly, while Klf was dispensable for S. Infantis colonization in the mouse, Ipf was required for maximal colonization in the murine ileum. In contrast to these phenotypes in mice, both Klf and Ipf contributed to a restrained infection in chicks, where the absence of these fimbriae has led to moderately higher bacterial burden in the avian host. Taken together, these data suggest that physiological differences between host species, such as the body temperature, can confer differences in fimbriome expression, affecting Salmonella colonization and other host-pathogen interplays.

Salmonella enterica serovar Infantis is one of the prevalent serovars worldwide and is often associated with human gastroenteritis and asymptomatic persistence in poultry. Different emergent S. Infantis populations were shown to acquire a large virulence-resistance plasmid, named pESI. Here we imaged and investigated the phylogenetic distribution, regulation and the role in virulence of two previously uncharacterized pESI-encoded fimbriae, designated Klf and Ipf. We elucidate their complex regulatory network involving core (ancestral) and horizontally acquired regulators and demonstrated that their expression is significantly induced under microaerobic conditions and at 41°C compared to 37°C or the ambient temperature. Furthermore, we established that Klf and Ipf present a different expression profile and play a distinct role during mouse and chick infection, characterized by body temperature of 37°C and 41.2°C, respectively. Different composition of fimbriae or even allelic variation within a particular fimbria contributes to host tropism and can change the interaction of Salmonella with its host. Our work suggests additional mechanism, by which fimbriome expression is altered in response to the physiological temperature of different hosts. A distinct repertoire of expressed fimbriae is expected to affect Salmonella colonization and modify the host immune response to its infection.

Salmonella infection: Interplay between the bacteria and host immune system

Salmonella infection causes morbidity and mortality throughout the world with the host immune response varying depending on whether the infection is acute and limited, or systemic and chronic. Additionally, Salmonella bacteria have evolved multiple mechanisms to avoid or subvert immunity to its own benefit and often the anatomical location of infection plays a role in both the immune response and bacterial fate. Here, we provide an overview of the interplay between the immune system and Salmonella, while discussing how different host and bacterial factors influence the outcome of infection.

Chronic Bacterial Pathogens: Mechanisms of Persistence

Many bacterial pathogens can cause acute infections that are cleared with the onset of adaptive immunity, but a subset of these pathogens can establish persistent, and sometimes lifelong, infections. While bacteria that cause chronic infections are phylogenetically diverse, they share common features in their interactions with the host that enable a protracted period of colonization. This article will compare the persistence strategies of two chronic pathogens from the Proteobacteria, Brucella abortus and Salmonella enterica serovar Typhi, to consider how these two pathogens, which are very different at the genomic level, can utilize common strategies to evade immune clearance to cause chronic intracellular infections of the mononuclear phagocyte system.

The malS-5′UTR regulates hisG, a key gene in the histidine biosynthetic pathway in Salmonella enterica serovar Typhi

Bacterial noncoding RNAs (ncRNA) regulate diverse cellular processes, including virulence and environmental fitness. The malS 5′ untranslated region (named malS-5′UTR) was identified as a regulatory ncRNA that increases the invasive capacity of Salmonella enterica serovar Typhi. An IntaRNA search suggested base pairing between malS-5′UTR and hisG mRNA, a key gene in the histidine biosynthetic pathway. Overexpression of malS-5′UTR markedly reduced bacterial growth in minimal medium without histidine. Overexpression of malS-5′UTR increased mRNA from his operon genes, independently of the bax gene, and decreased HisG protein in Salmonella Typhi. RNA structure analysis showed base pairing of the malS-5′UTR RNA with the hisG mRNA across the ribosome binding site. Thus, we propose that malS-5′UTR inhibited hisG translation, probably by base pairing to the Shine–Dalgarno sequence.

Emerging insights into the biology of typhoid toxin

Typhoid toxin is a unique A₂B₅ exotoxin and an important virulence factor for Salmonella Typhi, the cause of typhoid fever. In the decade since its initial discovery, great strides have been made in deciphering the unusual biological program of this toxin, which is fundamentally different from related toxins in many ways. Purified typhoid toxin administered to laboratory animals causes many of the symptoms of typhoid fever, suggesting that typhoid toxin is a central factor in this disease. Further advances in understanding the biology of this toxin will help guide the development of badly needed diagnostics and therapeutic interventions that target this toxin to detect, prevent or treat typhoid fever.

Differential roles for pathogenicity islands SPI-13 and SPI-8 in the interaction of Salmonella Enteritidis and Salmonella Typhi with murine and human macrophages

Background

Salmonella pathogenicity island (SPI)-13 is conserved in many serovars of S. enterica, including S. Enteritidis, S. Typhimurium and S. Gallinarum. However, it is absent in typhoid serovars such as S. Typhi and Paratyphi A, which carry SPI-8 at the same genomic location. Because the interaction with macrophages is a critical step in Salmonella pathogenicity, in this study we investigated the role played by SPI-13 and SPI-8 in the interaction of S. Enteritidis and S. Typhi with cultured murine (RAW264.7) and human (THP-1) macrophages.

Results

Our results showed that SPI-13 was required for internalization of S. Enteritidis in murine but not human macrophages. On the other hand, SPI-8 was not required for the interaction of S. Typhi with human or murine macrophages. Of note, the presence of an intact copy of SPI-13 in a S. Typhi mutant carrying a deletion of SPI-8 did not improve its ability to be internalized by, or survive in human or murine macrophages.

Conclusions

Altogether, our results point out to different roles for SPI-13 and SPI-8 during Salmonella infection. While SPI-13 contributes to the interaction of S. Enteritidis with murine macrophages, SPI-8 is not required in the interaction of S. Typhi with murine or human macrophages. We hypothesized that typhoid serovars have lost SPI-13 and maintained SPI-8 to improve their fitness during another phase of human infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s40659-017-0109-8) contains supplementary material, which is available to authorized users.

Animal Models for Salmonellosis: Applications in Vaccine Research

Salmonellosis remains an important cause of human disease worldwide. While there are several licensed vaccines for Salmonella enterica serovar Typhi, these vaccines are generally ineffective against other Salmonella serovars. Vaccines that target paratyphoid and nontyphoidal Salmonella serovars are very much in need. Preclinical evaluation of candidate vaccines is highly dependent on the availability of appropriate scientific tools, particularly animal models. Many different animal models exist for various Salmonella serovars, from whole-animal models to smaller models, such as those recently established in insects. Here, we discuss various mouse, rat, rabbit, calf, primate, and insect models for Salmonella infection, all of which have their place in research. However, choosing the right model is imperative in selecting the best vaccine candidates for further clinical testing. In this minireview, we summarize the various animal models that are used to assess salmonellosis, highlight some of the advantages and disadvantages of each, and discuss their value in vaccine development.

Typhoidal and non-typhoidal Salmonella infections in Africa

Salmonella infections in humans can range from self-limiting gastroenteritis typically associated with non-typhoidal Salmonella (NTS) to typhoidal fever, which can be life-threatening. Salmonellosis causes considerable morbidity and mortality in both humans and animals, and has a significant socioeconomic impact worldwide. In Africa, it is difficult to evaluate the situation of salmonellosis due to the non-availability of facilities capable of performing the tests essential for the diagnosis of typhoidal and non-typhoidal Salmonella infections. This article reviews important work in the literature, including the epidemiology, disease burden, pathogenesis, genomics, diagnosis, treatment, emergence and tracking of multidrug-resistant (MDR) Salmonella infections and intercontinental transmission of Salmonella to Africa. Searches of PubMed and Google Scholar were completed and the retrieved list of relevant publications were further screened. The literature revealed that the most common form of the disease in Africa is gastroenteritis, with bacterial multiplication in intestinal submucosa and diarrhoea caused by the inflammatory response and, perhaps, also by toxins. In addition to the high burden of Salmonella infection in Africa, MDR Salmonella species is on the rise in the continent, which might pose difficulties in the treatment of the disease.

RpoE promotes invasion and intracellular survival by regulating SPI-1 and SPI-2 in Salmonella enterica serovar Typhi

AIM

To demonstrate the role of RpoE during the later stage of hyperosmotic stress in Salmonella.

MATERIALS & METHODS

Expressions of SPI-1 and SPI-2 under hyperosmotic stress for 120 min were investigated by a microarray, and the invasion and intracellular survival of wild-type and ΔrpoE strains were compared. The global differential expression of bacterial proteins between the wild-type and ΔrpoE strains was examined after 120 min of hyperosmotic stress.

RESULTS

SPI-1 and SPI-2 were repressed, and the invasion and intracellular survival were defected in the ΔrpoE strain. Thirteen bacterial-associated proteins and 11 secreted proteins differed significantly between the wild-type and ΔrpoE strains.

CONCLUSION

RpoE may promote invasion and intracellular survival by regulating the expression of SPI-1 and SPI-2.

Typhoid toxin provides a window into typhoid fever and the biology of Salmonella Typhi

Salmonella Typhi is the cause of typhoid fever, a disease that has challenged humans throughout history and continues to be a major public health concern. Unlike infections with most other Salmonellae, which result in self-limiting gastroenteritis, typhoid fever is a life-threatening systemic disease. Furthermore, in contrast to most Salmonellae, which can infect a broad range of hosts, S. Typhi is a strict human pathogen. The unique features of S. Typhi pathogenesis and its stringent host specificity have been a long-standing puzzle. The discovery of typhoid toxin not only has provided major insight into these questions but also has offered unique opportunities to develop novel therapeutic and prevention strategies to combat typhoid fever.

Differences in Host Cell Invasion and Salmonella Pathogenicity Island 1 Expression between Salmonella enterica Serovar Paratyphi A and Nontyphoidal S. Typhimurium

Active invasion into nonphagocytic host cells is central to Salmonella enterica pathogenicity and dependent on multiple genes within Salmonella pathogenicity island 1 (SPI-1). Here, we explored the invasion phenotype and the expression of SPI-1 in the typhoidal serovarS Paratyphi A compared to that of the nontyphoidal serovarS Typhimurium. We demonstrate that while S. Typhimurium is equally invasive under both aerobic and microaerobic conditions, S. Paratyphi A invades only following growth under microaerobic conditions. Transcriptome sequencing (RNA-Seq), reverse transcription-PCR (RT-PCR), Western blot, and secretome analyses established that S. Paratyphi A expresses much lower levels of SPI-1 genes and secretes lesser amounts of SPI-1 effector proteins than S. Typhimurium, especially under aerobic growth. Bypassing the native SPI-1 regulation by inducible expression of the SPI-1 activator, HilA, considerably elevated SPI-1 gene expression, host cell invasion, disruption of epithelial integrity, and induction of proinflammatory cytokine secretion by S. Paratyphi A but not by S. Typhimurium, suggesting that SPI-1 expression is naturally downregulated inS Paratyphi A. Using streptomycin-treated mice, we were able to establish substantial intestinal colonization byS Paratyphi A and showed moderately higher pathology and intestinal inflammation in mice infected with S. Paratyphi A overexpressing hilA Collectively, our results reveal unexpected differences in SPI-1 expression between S. Paratyphi A andS Typhimurium, indicate that S. Paratyphi A host cell invasion is suppressed under aerobic conditions, and suggest that lower invasion in aerobic sites and suppressed expression of immunogenic SPI-1 components contributes to the restrained inflammatory infection elicited by S. Paratyphi A.

A repertoire of high-affinity monoclonal antibodies specific to S. typhi: as potential candidate for improved typhoid diagnostic

Typhoid fever is a significant global health problem with highest burden on the developing world. The severity of typhoid is often underestimated, and currently available serological diagnostic assays are inadequate due to lack in requisite sensitivity and specificity. This underlines an absolute need to develop a reliable and accurate diagnostics that would benefit long-term disease control and treatment and to understand the real disease burden. Here, we have utilized flagellin protein of S. typhi that is surface accessible, abundantly expressed, and highly immunogenic, for developing immunodiagnostic tests. Flagellin monomers are composed of conserved amino-terminal and carboxy-terminal, and serovar-specific middle region. We have generated a panel of murine monoclonal antibodies (mAbs) against the middle region of flagellin, purified from large culture of S. typhi to ensure its native conformation. These mAbs showed unique specificity and very high affinity toward S. typhi flagellin without showing any cross-reactivity with other serovars. Genetic analysis of mAbs also revealed high frequency of somatic mutation due to antigenic selection process across variable region to achieve high binding affinity. These antibodies also displayed stable binding in stringent reaction conditions for antigen-antibody interactions, like DMSO, urea, KSCN, guanidinium HCl, and extremes of pH. One of the mAbs potentially reversed the TLR5-mediated immune response, in vitro by inhibiting TLR5-flagellin interaction. In our study, binding of these mAbs to flagellin, with high affinity, present on bacterial surface, as well as in soluble form, validates their potential use in developing improved diagnostics with significantly higher sensitivity and specificity.

Mechanisms of Salmonella Typhi Host Restriction

Salmonella enterica serovar Typhi (S. Typhi) is the cause of typhoid fever, a life-threatening bacterial infection that is very common in the developing world. Recent spread of antimicrobial resistant isolates of S. Typhi makes typhoid fever, a global public health risk. Despite being a common disease, still very little is known about the molecular mechanisms underlying typhoid fever and S. Typhi pathogenesis. In contrast to other Salmonellae, S. Typhi can only infect humans. The molecular bases of this human restriction are mostly unknown. Recent studies identified a novel pathway that contributes to S. Typhi human restriction and is required for killing S. Typhi in macrophages of nonsusceptible species. The small Rab GTPase Rab32 and its guanine nucleotide exchange factor BLOC-3 are the critical components of this pathway. These proteins were already well known as important regulators of intracellular membrane transport. In particular, they are central for the transport of enzymes that synthetize melanin in pigment cells. The recent findings that Rab32 and BLOC-3 are required for S. Typhi host restriction point out to a novel mechanism restricting the growth of bacterial pathogen, dependent on the transport of still unknown molecule(s) to the S. Typhi vacuole. The identification of this novel antimicrobial pathway constitutes a critical starting point to study molecular mechanisms killing bacterial pathogens and possibly identify novel antimicrobial molecules.

Invasive Salmonellosis in Humans

Human salmonellosis is generally associated with Salmonella enterica from subspecies enterica (subspecies I). Acute infections can present in one of four ways: enteric fever, gastroenteritis, bacteremia, or extraintestinal focal infection. As with other infectious diseases, the course and outcome of the infection depend on a variety of factors, including the infecting organism, the inoculating dose, and the immune status and genetic background of the host. For serovarsTyphi and Paratyphi A there is a clear association between the genetic background of the serovar and systemic infection in humans. For serovars Paratyphi B and Paratyphi C, a good clinical description of the host and detailed population genetics of the pathogen are necessary before more detailed genetic studies of novel virulence factors,or host factors,can be initiated. For the nontyphoidalserovars (NTS) the situation is less clear. Serovars Typhimurium and Enteritidis are the most common within the food chain, and so the large number of invasive infections associated with these serovars is most likely due to exposure rather than to increased virulence of the pathogen. In Africa, however, a closely related group of strains of serovar Typhimurium, associated with HIV infection, may have become host adapted tohumans, suggesting that not all isolates called "Typhimurium" should be considered as a single group. Here we review current knowledge of the salmonellae for which invasive disease in humans is an important aspect of their population biology.

Protective host immune responses to Salmonella infection

Salmonella enterica serovars Typhi and Paratyphi are the causative agents of human typhoid fever. Current typhoid vaccines are ineffective and are not widely used in endemic areas. Greater understanding of host-pathogen interactions during Salmonella infection should facilitate the development of improved vaccines to combat typhoid and nontyphoidal Salmonellosis. This review will focus on our current understanding of Salmonella pathogenesis and the major host immune components that participate in immunity to Salmonella infection. In addition, recent findings regarding host immune mechanisms in response to Salmonella infection will be also discussed, providing a new perspective on the utility of improved tools to study the immune response to Salmonella infections.

Salmonella Infections in Childhood

Salmonella are gram-negative bacilli within the family Enterobacteriaceae. They are the cause of significant morbidity and mortality worldwide. Animals (pets) are an important reservoir for nontyphoidal Salmonella, whereas humans are the only natural host and reservoir for Salmonella Typhi. Salmonella infections are a major cause of gastroenteritis worldwide. They account for an estimated 2.8 billion cases of diarrheal disease each year. The transmission of Salmonella is frequently associated with the consumption of contaminated water and food of animal origin, and it is facilitated by conditions of poor hygiene. Nontyphoidal Salmonella infections have a worldwide distribution, whereas most typhoidal Salmonella infections in the United States are acquired abroad. In the United States, Salmonella is a common agent for food-borne–associated infections. Several outbreaks have been identified and are most commonly associated with agricultural products. Nontyphoidal Salmonella infection is usually characterized by a self-limited gastroenteritis in immunocompetent hosts in industrialized countries, but it may also cause invasive disease in vulnerable individuals (eg, children less than 1 year of age, immunocompromised). Antibiotic treatment is not recommended for treatment of mild to moderate gastroenteritis by nontyphoidal Salmonella in immunocompetent adults or children more than 1 year of age. Antibiotic treatment is recommended for nontyphoidal Salmonella infections in infants less than 3 months of age, because they are at higher risk for bacteremia and extraintestinal complications. Typhoid (enteric) fever and its potential complications have a significant impact on children, especially those who live in developing countries. Antibiotic treatment of typhoid fever has become challenging because of the emergence of Salmonella Typhi strains that are resistant to classically used first-line agents: ampicillin, trimethoprim-sulfamethoxazole, and chloramphenicol. The choice of antibiotics for the management of typhoid fever should be guided by the local resistance pattern. Recommendations include using an extended spectrum cephalosporin, azithromycin, or a fluoroquinolone. Fecal carriage of Salmonella is an important factor in the spread of the organism to healthy individuals. The most important measures to prevent the spread and outbreaks of Salmonella infections and typhoid fever are adequate sanitation protocols for food processing and handling as well as hand hygiene. In the United States, 2 vaccines are commercially available against Salmonella Typhi. The WHO recommends the use of these vaccines in endemic areas and for outbreak control.

Decrease of colonization in the chicks' cecum and internal organs of Salmonella enterica serovar Pullorum by deletion of cpdB by Red system

Salmonella enterica serovar Pullorum (S. Pullorum) is a worldwide poultry pathogen of considerable economic importance, particularly in those countries with a developing poultry industry. A variety of genes that affect S. Pullorum colonization in chickens had been identified. 2',3'-cyclic phosphodiesterase (cpdB) is the bifunctional enzyme which possess 2',3'-cyclic phosphodiesterase as well as 3'-nucleotidase activity. To assess the role of cpdB of S. Pullorum in colonization of cecum and internal organs in poultry, seven-day-old chicks were infected with 10(9) CFU/ml of a cpdB mutant and wild type strain. High number of cpdB mutant and wild type strain colonized the internal organs shortly after infection, but no colonization of cpdB mutant were observed from internal organs at day 10 post-infection, meanwhile, wild type bacteria in internal organs were observed at day 16 post-infection. Furthermore, the colonization of cpdB mutant in the cecum was seriously decreased from 6 days post-infection simultaneously wild type strain was increased and seriously decreased at day 8 post-infection. At day 12 post-infection, no cpdB mutant was observed from cecum, however high numbers of wild type strain were isolated at day 16 post-infection. It is concluded that cpdB is involved in long-term colonization of S. Pullorum in the chicks' cecum and internal organs. In addition, deletion of cpdB from S. Pullorum was not affect the morphology and growth of bacteria.

Acute scrotal ulcers in typhoid Fever: case report and literature review

Background. In developed countries, typhoid fever is a travel-associated disease that is often overlooked. However, as standard blood and stool culture methods have relatively low sensitivity, diagnosis depends heavily on clinical signs and symptoms and on a high level of suspicion.

Methods. Reported here is the case of an 18-year-old male who presented with fever and acute scrotal ulcers and whose blood cultures were positive for Salmonella enterica serotype Typhi. A review of genital ulcers associated with typhoid fever in the literature is discussed.

Conclusion. This report suggests that typhoid fever is a differential diagnosis of acute genital ulcers.

Mouse ENU Mutagenesis to Understand Immunity to Infection: Methods, Selected Examples, and Perspectives

Infectious diseases are responsible for over 25% of deaths globally, but many more individuals are exposed to deadly pathogens. The outcome of infection results from a set of diverse factors including pathogen virulence factors, the environment, and the genetic make-up of the host. The completion of the human reference genome sequence in 2004 along with technological advances have tremendously accelerated and renovated the tools to study the genetic etiology of infectious diseases in humans and its best characterized mammalian model, the mouse. Advancements in mouse genomic resources have accelerated genome-wide functional approaches, such as gene-driven and phenotype-driven mutagenesis, bringing to the fore the use of mouse models that reproduce accurately many aspects of the pathogenesis of human infectious diseases. Treatment with the mutagen N-ethyl-N-nitrosourea (ENU) has become the most popular phenotype-driven approach. Our team and others have employed mouse ENU mutagenesis to identify host genes that directly impact susceptibility to pathogens of global significance. In this review, we first describe the strategies and tools used in mouse genetics to understand immunity to infection with special emphasis on chemical mutagenesis of the mouse germ-line together with current strategies to efficiently identify functional mutations using next generation sequencing. Then, we highlight illustrative examples of genes, proteins, and cellular signatures that have been revealed by ENU screens and have been shown to be involved in susceptibility or resistance to infectious diseases caused by parasites, bacteria, and viruses.

Phosphoinositides and host-pathogen interactions

Phosphoinositides control key cellular processes including vesicular trafficking and actin polymerization. Intracellular bacterial pathogens manipulate phosphoinositide metabolism in order to promote their uptake by target cells and to direct in some cases the biogenesis of their replication compartments. In this chapter, we review the molecular strategies that major pathogens including Listeria, Mycobacterium, Shigella, Salmonella, Legionella and Yersinia use to hijack phosphoinositides during infection. This article is part of a Special Issue entitled Phosphoinositides.

How multidrug resistance in typhoid fever affects treatment options

Salmonella enterica serotype Typhi (S. Typhi) is an enteric pathogen that causes typhoid fever. The infection can be severe, with significant morbidity and mortality, requiring antimicrobial therapy. Cases of S. Typhi infection in the United States and other developed countries are often associated with travel to endemic regions. The empirical use of first-line drugs for therapy, including ampicillin, chloramphenicol, and trimethoprim/sulfamethoxazole, has resulted in transmissible multidrug resistance. With the global increase in multidrug-resistant S. Typhi, use of ciprofloxacin, with excellent oral absorption, few side effects, and cost-effectiveness, has become popular for treatment. However, decreased ciprofloxacin susceptibility due to point mutations in the S. Typhi genes gyrA and/or parC has caused treatment failures, necessitating alternative therapeutic options. S. Typhi is typically genetically homogenous, with phylogenetic and epidemiological studies showing that identical clones and diverse S. Typhi types often coexist in the same geographic region. Studies investigating point mutations have demonstrated that selective pressure from empirical use of first-line drugs and fluoroquinolones has led to the global emergence of haplotype H-58. Antibiotic resistance is subject to high selective pressure in S. Typhi and thus demands careful use of antimicrobials.

Salmonella require the fatty acid regulator PPARδ for the establishment of a metabolic environment essential for long-term persistence

Host-adapted Salmonella strains are responsible for a number of disease manifestations in mammals, including an asymptomatic chronic infection in which bacteria survive within macrophages located in systemic sites. However, the host cell physiology and metabolic requirements supporting bacterial persistence are poorly understood. In a mouse model of long-term infection, we found that S. typhimurium preferentially associates with anti-inflammatory/M2 macrophages at later stages of infection. Further, PPARδ, a eukaryotic transcription factor involved in sustaining fatty acid metabolism, is upregulated in Salmonella-infected macrophages. PPARδ deficiency dramatically inhibits Salmonella replication, which is linked to the metabolic state of macrophages and the level of intracellular glucose available to bacteria. Pharmacological activation of PPARδ increases glucose availability and enhances bacterial replication in macrophages and mice, while Salmonella fail to persist in Pparδ null mice. These data suggest that M2 macrophages represent a unique niche for long-term intracellular bacterial survival and link the PPARδ-regulated metabolic state of the host cell to persistent bacterial infection.

Dietary supplementation with white button mushrooms augments the protective immune response to Salmonella vaccine in mice

We previously showed that dietary white button mushrooms (WBMs) enhanced natural killer cell activity and that in vitro WBM supplementation promotes maturation and function of dendritic cells (DCs). The current study investigated whether WBM consumption would enhance pathogen-specific immune response using a Salmonella vaccination and infection animal model. C57BL/6 mice were fed diets containing 0%, 2%, or 5% WBM for 4 wk before oral vaccination with live attenuated Salmonella typhimurium SL1479. Four weeks after immunization, mice were orally infected with virulent Salmonella typhimurium SL1344. Immunization increased animal survival and, among immunized mice, the 2% WBM group had a higher survival rate than the other groups. Next, we fed mice 2% WBMs to determine the immunological mechanism underlying the WBM-potentiated protective effect. We found that WBM supplementation increased Salmonella-specific blood immunoglobulin (Ig) G and fecal IgA concentrations. WBM-fed mice also had a higher IgG2a and unchanged IgG1 production, leading to an elevated IgG2a:IgG1 ratio and indicating an enhanced T helper 1 response. Consistent with these results, WBM-fed mice had higher interferon-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-17A production and unchanged IL-4 production in their splenocytes after polyclonal (anti-CD3/CD28) or antigen-specific stimulation. Furthermore, WBM-fed mice had more DCs in the spleen, and these DCs expressed higher levels of activation markers CD40 and major histocompatibility complex-II. These mice also produced more IL-12 and TNF-α postimmunization. Together, these results suggest that WBMs may improve Salmonella vaccine efficacy through an enhanced adaptive immune response.

Characterization of the yehUT two-component regulatory system of Salmonella enterica Serovar Typhi and Typhimurium

Proteins exhibiting hyper-variable sequences within a bacterial pathogen may be associated with host adaptation. Several lineages of the monophyletic pathogen Salmonella enterica serovar Typhi (S. Typhi) have accumulated non-synonymous mutations in the putative two-component regulatory system yehUT. Consequently we evaluated the function of yehUT in S. Typhi BRD948 and S. Typhimurium ST4/74. Transcriptome analysis identified the cstA gene, encoding a carbon starvation protein as the predominantly yehUT regulated gene in both these serovars. Deletion of yehUT had no detectable effect on the ability of these mutant Salmonella to invade cultured epithelial cells (S. Typhi and S. Typhimurium) or induce colitis in a murine model (S. Typhimurium only). Growth, metabolic and antimicrobial susceptibility tests identified no obvious influences of yehUT on these phenotypes.