Global trends in typhoid and paratyphoid Fever

Antimicrobial Resistance in Salmonella Typhi Isolated From a Referral Hospital of Kathmandu, Nepal

Purpose:

The morbidity and mortality due to typhoid fever can be significantly reduced with the use of effective antibiotics. At present, fluoroquinolones, third generation cephalosporins, and azithromycin are widely used to treat typhoid fever. However, changing antibiotic susceptibility among Salmonella Typhi and Salmonella Paratyphi poses a particular challenge to the therapeutic management of enteric fever. The objective of this study was to assess the antibiotic susceptibility pattern of Salmonella Typhi isolates.

Patients and Methods:

A total of 706 blood specimens were collected from febrile patients attending the outpatient department of Kathmandu Model Hospital during June to September, 2018. The antibiotic susceptibility testing for 11 different antibiotics (nalidixic acid, ciprofloxacin, ofloxacin, levofloxacin, cefixime, ceftriaxone, cefotaxime, azithromycin, cotrimoxazole, chloramphenicol, and amoxicillin) was performed by disk diffusion method. Furthermore, minimum inhibitory concentration (MIC) values of ciprofloxacin, ofloxacin, and azithromycin were determined by agar dilution method. Mutation at gyrA ser83 associated with reduced susceptibility to fluoroquinolones was determined by PCR-RFLP.

Results:

Out of 706 blood samples, 6.94% (n = 49) were culture positive for Salmonella enterica (S. Typhi, n = 46). It was revealed that 97.8% S. Typhi isolates were susceptible to conventional first-line antibiotics (ampicillin, chloramphenicol, and cotrimoxazole), 97.3% to cephalosporins and 95.7% to azithromycin. S. Typhi were either resistant or intermediately susceptible to fluoroquinolones: 97.8% to ciprofloxacin, 91.3% to ofloxacin, and 89.1% to levofloxacin. The MIC of ciprofloxacin, ofloxacin, and azithromycin for S. Typhi ranged from 0.008 to 32, 0.03 to 16, and 2 to 8 μg/mL, respectively. Out of 46 S. Typhi isolates, 44 (95.65%) had gyrA ser83 mutation.

Conclusion:

Fluoroquinolones have poor activity against Salmonella Typhi. The trends of increasing azithromycin MIC value among S. Typhi might limit its use for the treatment of typhoid fever. Effectiveness of conventional first-line antibiotics in vitro suggests considering their clinical use after large-scale studies.

Prevalence and awareness of mode of transmission of typhoid fever in patients diagnosed with Salmonella typhi and paratyphi infections at the Saint Elisabeth General Hospital Shisong, Bui Division, Cameroon

Introduction

typhoid fever is a systemic infectious disease caused by the bacteria Salmonella enterica subspecies (typhi). It is a major cause of morbidity and mortality worldwide. This cross-sectional descriptive study aimed at determining the prevalence and awareness of the mode of transmission of Salmonella typhi among patients at the Saint Elisabeth General Hospital Shisong of Cameroon.

Methods

the study carried out from March 1^st, 2017 to May 31^st, 2017 recruited patients who presented at the hospital with clinical signs and symptoms of typhoid fever and who had lab requests for stool culture requested by the resident physician. The prevalence of Salmonella typhi infections among the patients and the proportion of patients with adequate knowledge on the mode of transmission of Salmonella typhi were estimated at a 95% CI. Data were analyzed using Epi info7.1.3.3.

Results

out of the 172 patients recruited for the studies, 52 (30.1%) were diagnosed with Salmonella typhi, 59.6% of which were male. Also, 3 (5.8%) were diagnosed with Salmonella paratyphoid A. A positive correlation between knowledge on the mode of transmission of Salmonella typhi and the level of education was established, showing that 92% of participants with a higher level of education indicating that typhoid fever can be contracted through consumption of contaminated water.

Conclusion

high prevalence of typhoid fever was observed in our study. The unawareness of the patients on typhoid fever and its contraction through contaminated water and food was positively correlated to the level of educations of the patients. These findings, therefore, suggest a public health challenge faced by inhabitants in this region where typhoid fever remains endemic. Scarcity of potable water, improper drainage systems, and problems of unsanitary toilets in Cameroon require urgent intervention.

Pathogenicity of Salmonella During Schistosoma-Salmonella Co-infections and the Importance of the Gut Microbiota

Antibiotic inefficacy in treating bacterial infections is largely studied in the context of developing resistance mechanisms. However, little attention has been paid to combined diseases mechanisms, interspecies pathogenesis and the resulting impact on antimicrobial treatment. This review will consider the co-infections of Salmonella and Schistosoma mansoni. It summarises the protective mechanisms that the pathophysiology of the two infections confer, which leads to an antibiotic protection phenomenon. This review will elucidate the functional characteristics of the gut microbiota in the context of these co-infections, the pathogenicity of these infections in infected mice, and the efficacy of the antibiotics used in treatment of these co-infections over time. Salmonella-Schistosoma interactions and the mechanism for antibiotic protection are not well established. However, antimicrobial drug inefficacy is an existing phenomenon in these co-infections. The treatment of schistosomiasis to ensure the efficacy of antibiotic therapy for bacterial infections should be considered in co-infected patients.

Whole-Genome Analysis of Multidrug-Resistant Salmonella Enteritidis Strains Isolated from Poultry Sources in Korea

The Salmonella Enterica subsp. Enterica serovar Enteritidis is one of main serovars isolated from human patients with food poisoning and poultry without clinical signs. Consumption of poultry products contaminated with Salmonella Enteritidis is a common source of human salmonellosis; 82 Salmonella spp. were isolated from 291 samples of retail chicken meat, 201 one-day-old chicks, 30 internal organs of chickens, 156 chicken eggs, 100 duck eggs, 38 straw bedding samples, 18 samples of retail duck meat, and 19 swab samples from slaughterhouses in 2019 and 2020. An antibiotic susceptibility test was performed for all isolates, revealing 33 multidrug-resistant (MDR) strains. The whole genome of 33 MDR strains isolated in 2019 and 2020 and 10 strains isolated in 2011, 2012, and 2017 was sequenced using the MinION sequencing protocol. Within these 43 samples, 5 serovars were identified: S. Enteritidis, S. Agona, S. Virchow, S. Albany, and S. Bareilly. The most common serovar was S. Enteritidis (26/43), which showed the highest resistance to ampicillin (100%), followed by nalidixic acid (90%) and colistin (83%). Core genome multilocus sequence typing analysis showed that the S. Enteritidis strains isolated from different sources and in different years were clustered together. In addition, the S. Enteritidis strains isolated since 2011 consistently harbored the same antibiotic resistance patterns.

Massive Gastrointestinal Hemorrhage Secondary to Typhoid Fever

Typhoid fever is caused by Salmonella typhi, a gram-negative organism. The disease usually presents with high-grade fever, abdominal pain, and diarrhea. Gastrointestinal hemorrhage is a frequent complication of the disease. However, adequate treatment with antibiotics has lowered the rate of complications. We present the case of a 21-year-old male who was admitted to the hospital with high-grade fever and per rectal bleeding. A few hours after admission, the patient had episodes of massive per rectal bleeding which resulted in hemodynamic instability. The bleeding was then successfully controlled with endoscopic hemoclipping. Concurrently, his blood culture results showed growth of Salmonella typhi for which antibiotic therapy was initiated, and the patient's condition improved thereafter. This report highlights the rare occurrence of massive lower gastrointestinal bleeding in patients with typhoid fever. It also signifies the use of endoscopic therapy with endoclips for the management of massive lower gastrointestinal bleeding. 

The molecular basis of extensively drug-resistant Salmonella Typhi isolates from pediatric septicemia patients

Sepsis is a syndromic response to infections and is becoming an emerging threat to the public health sector, particularly in developing countries. Salmonella Typhi (S. Typhi), the cause of typhoid fever, is one primary cause of pediatric sepsis in typhoid endemic areas. Extensively drug-resistant (XDR) S. Typhi is more common among pediatric patients, which is responsible for over 90% of the reported XDR typhoid cases, but the majority of antibiotic resistance studies available have been carried out using S. Typhi isolates from adult patients. Here, we characterized antibiotic-resistance profiles of XDR S. Typhi isolates from a medium size cohort of pediatric typhoid patients (n = 45, 68.89% male and 31.11% female) and determined antibiotic-resistance-related gene signatures associated with common treatment options to typhoid fever patients of 18 XDR S. Typhi representing all 45 isolates. Their ages were 1–13 years old: toddlers aging 1–2 years old (n = 9, 20%), pre-schoolers aging 3–5 years old (n = 17, 37.78%), school-age children aging 6–12 years old (n = 17, 37.78%), and adolescents aging 13–18 years old (n = 2, 4.44%). Through analyzing bla_TEM1, dhfR7, sul1, and catA1genes for multidrug-resistance, qnrS, gyrA, gyrB, parC, and parE for fluoroquinolone-resistance, bla_CTX-M-15 for XDR, and macAB and acrAB efflux pump system-associated genes, we showed the phenotype of the XDR S. Typhi isolates matches with their genotypes featured by the acquisitions of the genes bla_TEM1, dhfR7, sul1, catA1, qnrS, and bla_CTX-M-15 and a point mutation on gyrA. This study informs the molecular basis of antibiotic-resistance among recent S. Typhi isolates from pediatric septicemia patients, therefore providing insights into the development of molecular detection methods and treatment strategies for XDR S. Typhi.

Investigating the Efficiency of Recombinant FliC-Loaded Bacillus subtilis Spores in Mice Immunization against Salmonella enterica Serovar Typhi

Background:

Bacterial spores are among the most efficient vaccine delivery vehicles. Because of their safety and efficacy, Bacillus subtilis spores are increasingly used in this regard. The negatively charged surfaces of the spores allow antigens to be adsorbed onto these structures. In this study, a candidate vaccine against Salmonella enterica serovar Typhi was adsorbed onto B. subtilis spores and the immunogenicity of the formulation was investigated in BALB/c mice.

Methods:

This work was performed during 2018–2019 in Islamic Azad University of Lahijan. FliC protein was recombinantly expressed in E. coli BL21 (DE3) cells and purified by affinity chromatography. On the other hand, B. subtilis strain PY79 (ATCC1609) was cultured in DSM medium and after the sporulation, FliC protein was adsorbed onto the spores in three different pH values (4, 7 and 10) and the adsorption was verified using dot-blot assay. FliC-adsorbed spores were then administered to BALB/c mice through the subcutaneous route. Mice immunization was evaluated by serum IgG assessment and challenge study.

Results:

FliC protein was successfully expressed and purified. Sporulation was controlled by phase-contrast microscopy. Serum IgG assay showed significant stimulation of the mice’s humoral immune system. Immunized mice were able to resist bacterial infection.

Conclusion:

The results showed the efficiency of spores as natural adjuvants for the stimulation of mice immune system. The formulation can be exploited for the delivery of recombinant vaccines against bacterial pathogens.

Multiple introductions of multidrug-resistant typhoid associated with acute infection and asymptomatic carriage, Kenya

Background:

Understanding the dynamics of infection and carriage of typhoid in endemic settings is critical to finding solutions to prevention and control.

Methods:

In a 3-year case-control study, we investigated typhoid among children aged <16 years (4670 febrile cases and 8549 age matched controls) living in an informal settlement, Nairobi, Kenya.

Results:

148 S. Typhi isolates from cases and 95 from controls (stool culture) were identified; a carriage frequency of 1 %. Whole-genome sequencing showed 97% of cases and 88% of controls were genotype 4.3.1 (Haplotype 58), with the majority of each (76% and 88%) being multidrug-resistant strains in three sublineages of the H58 genotype (East Africa 1 (EA1), EA2, and EA3), with sequences from cases and carriers intermingled.

Conclusions:

The high rate of multidrug-resistant H58 S. Typhi, and the close phylogenetic relationships between cases and controls, provides evidence for the role of carriers as a reservoir for the community spread of typhoid in this setting.

Funding:

National Institutes of Health (R01AI099525); Wellcome Trust (106158/Z/14/Z); European Commission (TyphiNET No 845681); National Institute for Health Research (NIHR); Bill and Melinda Gates Foundation (OPP1175797).

Prioritization of potential vaccine candidates and designing a multiepitope-based subunit vaccine against multidrug-resistant Salmonella Typhi str. CT18: A subtractive proteomics and immunoinformatics approach

Salmonella enterica serovar Typhi (S. Typhi), a causative agent of typhoid fever, is a Gram-negative, human-restricted pathogen that causes significant morbidity and mortality, particularly in developing countries. The currently available typhoid vaccines are not recommended to children below six years of age and have poor long-term efficacy. Due to these limitations and the emerging threat of multidrug-resistance (MDR) strains, the development of a new vaccine is urgently needed. The present study aims to design a multiepitope-based subunit vaccine (MESV) against MDR S. Typhi str. CT18 using a computational-based approach comprising subtractive proteomics and immunoinformatics. Firstly, we investigated the proteome of S. Typhi str. CT18 using subtractive proteomics and identified twelve essential, virulent, host non-homologous, and antigenic outer membrane proteins (OMPs) as potential vaccine candidates with low transmembrane helices (≤1) and molecular weight (≤110 kDa). The OMPs were mapped for cytotoxic T lymphocyte(CTL) epitopes, helper T lymphocyte (HTL) epitopes, and linear B lymphocyte (LBL) epitopes using various immunoinformatics tools and servers. A total of 6, 12, and 11 CTL, HTL, and LBL epitopes were shortlisted, respectively, based on their immunogenicity, antigenicity, allergenicity, toxicity, and hydropathicity potential. Four MESV constructs (MESVCs), MESVC-1, MESVC-2, MESVC-3, and MESVC-4, were designed by linking the CTL, HTL, and LBL epitopes with immune-modulating adjuvants, linkers, and PADRE (Pan HLA DR-binding epitope) sequences. The MESVCs were evaluated for their physicochemical properties, allergenicity, antigenicity, toxicity, and solubility potential to ensure their safety and immunogenic behavior. Secondary and tertiary structures of shortlisted MESVCs (MESVC-1, MESVC-3, and MESVC-4) were predicted, modeled, refined, validated, and then docked with various MHC I, MHC II, and TLR4/MD2 complex. Molecular dynamics (MD) simulation of the final selected MESVC-4 with TLR4/MD2 complex confirms its binding affinity and stability. Codon optimization and in silico cloning verified the translation efficiency and successful expression of MESVC-4 in E. coli str. K12. Finally, the efficiency of MESVC-4 to trigger an effective immune response was assessed by an in silico immune simulation. In conclusion, our findings show that the designed MESVC-4 can elicit humoral and cellular immune responses, implying that it may be used for prophylactic or therapeutic purposes. Therefore, it should be subjected to further experimental validations.

A Cross-Sectional Comparative Study of the Performance of the Widal Test and the Typhidot Immunoassay for Typhoid Fever Diagnosis in the West Region of Cameroon

Background

The diagnosis of typhoid fever based on the Widal slide agglutination test remains a major hurdle in developing countries due to varied perceptions of the value of the Widal test in determining clinical decision-making. We undertook a study to evaluate the diagnostic performance of the Widal test and the Typhidot immunoassay in patients suspected of having typhoid fever in the Menoua division, West Region of Cameroon.

Methods

Blood and stool samples were collected from 558 consenting febrile patients on the basis of suspicion of typhoid fever. These patients attended three district health services of the Menoua division between April 2018 and September 2019. These patients had clinical symptoms suggestive of typhoid fever as determined by their consultant. Serum was used for the Widal slide agglutination test and for the Typhidot rapid immunoassay test based on manufacturer's guidelines. A composite reference of fever plus positive coproculture for Salmonella typhi and Salmonella paratyphi was used as the reference. The sensitivity, specificity, and predictive values of the positive and negative tests were calculated as well as Cohen's kappa for agreement between the two tests.

Results

Of 558 patients, 12.90% tested positive for the reference method, 57.17% tested positive for the Widal slide agglutination test, while 15.59% were positive for Typhidot-IgM. The overall sensitivity, specificity, and predictive values of the positive and negative tests were 80.56%, 94.03%, 66.6%, and 97.03% for Typhidot-IgM and 94.44%, 48.35%, 21.32%, and 98.33% for the Widal slide agglutination test, respectively. Cohen's kappa estimates were 0.1660 (0.121–0.211) and 0.386 (0.312–0.460) for the Widal test and Typhidot immunoassay for 53.6% and 76.16% agreements of all observations, respectively.

Conclusion

The Widal test was found to have a lower predictive value for the diagnosis of typhoid fever in our setting. However, the Typhidot test, although better, was not ideal. Diagnosis of typhoid fever should therefore rely on adequate clinical suspicion and a positive Typhidot test to improve the clinical management of typhoid fever in our setting.

Increasingly limited options for the treatment of enteric fever in travellers returning to England, 2014-2019: a cross-sectional analytical study

Introduction. Enteric fever (caused by Salmonella enterica serovars Typhi and Paratyphi) frequently presents as an acute, undifferentiated febrile illness in returning travellers, requiring timely empirical antibiotics.Gap Statement. Determining which empirical antibiotics to prescribe for enteric fever requires up-to-date knowledge of susceptibility patterns.Aim. By characterising factors associated with antimicrobial resistance in cases of S. Typhi and S. Paratyphi imported to England, we aim to guide effective empirical treatment.Methodology. All English isolates of S. Typhi and S. Paratyphi 2014-2019 underwent antimicrobial susceptibility testing; results were compared to a previous survey in London 2005-2012. Risk factors for antimicrobial resistance were analysed with logistic regression models to predict adjusted odds ratios (aOR) for resistance to individual antibiotics and multi-drug resistance.Results. We identified 1088 cases of S. Typhi, 729 S. Paratyphi A, 93 S. Paratyphi B, and one S. Paratyphi C. In total, 93 % were imported. Overall, 90 % of S. Typhi and 97 % of S. Paratyphi A isolates were resistant to ciprofloxacin; 26 % of S. Typhi were multidrug resistant to ciprofloxacin, amoxicillin, co-trimoxazole, and chloramphenicol (MDR+FQ). Of the isolates, 4 % of S. Typhi showed an extended drug resistance (XDR) phenotype of MDR+FQ plus resistance to third-generation cephalosporins, with cases of XDR rising sharply in recent years (none before 2017, one in 2017, six in 2018, 32 in 2019). For S. Typhi isolates, resistance to ciprofloxacin was associated with travel to Pakistan (aOR=32.0, 95 % CI: 15.4-66.4), India (aOR=21.8, 95 % CI: 11.6-41.2), and Bangladesh (aOR=6.2, 95 % CI: 2.8-13.6) compared to travel elsewhere, after adjusting for rising prevalence of resistance over time. MDR+FQ resistance in S. Typhi isolates was associated with travel to Pakistan (aOR=3.5, 95 % CI: 2.4-5.2) and less likely with travel to India (aOR=0.07, 95 % CI 0.04-0.15) compared to travel elsewhere. All XDR cases were imported from Pakistan. No isolate was resistant to azithromycin. Comparison with the 2005-2012 London survey indicates substantial increases in the prevalence of resistance of S. Typhi isolates to ciprofloxacin associated with travel to Pakistan (from 79-98 %) and Africa (from 12-60 %).Conclusion. Third-generation cephalosporins and azithromycin remain appropriate choices for empirical treatment of enteric fever in most returning travellers to the UK from endemic countries, except from Pakistan, where XDR represents a significant risk.

Phylogenomics and antimicrobial resistance of Salmonella Typhi and Paratyphi A, B and C in England, 2016-2019

The emergence of antimicrobial resistance (AMR) to first- and second-line treatment regimens of enteric fever is a global public-health problem, and routine genomic surveillance to inform clinical and public-health management guidance is essential. Here, we present the prospective analysis of genomic data to monitor trends in incidence, AMR and travel, and assess hierarchical clustering (HierCC) methodology of 1742 isolates of typhoidal salmonellae. Trend analysis of Salmonella Typhi and S. Paratyphi A cases per year increased 48 and 17.3%, respectively, between 2016 and 2019 in England, mainly associated with travel to South Asia. S. Paratyphi B cases have remained stable and are mainly associated with travel to the Middle East and South America. There has been an increase in the number of S. Typhi exhibiting a multidrug-resistant (MDR) profile and the emergence of extensively drug resistant (XDR) profiles. HierCC was a robust method to categorize clonal groups into clades and clusters associated with travel and AMR profiles. The majority of cases that had XDR S. Typhi reported recent travel to Pakistan (94 %) and belonged to a subpopulation of the 4.3.1 (H58) clone (HC5_1452). The phenotypic and genotypic AMR results showed high concordance for S. Typhi and S. Paratyphi A, B and C, with 99.99 % concordance and only three (0.01 %) discordant results out of a possible 23 178 isolate/antibiotic combinations. Genomic surveillance of enteric fever has shown the recent emergence and increase of MDR and XDR S. Typhi strains, resulting in a review of clinical guidelines to improve management of imported infections.

Salmonella Typhi from Northwest Pakistan: Molecular Strain Typing and Drug Resistance Signature

Objective: To determine the molecular strain typing and drug resistance pattern of Salmonella enterica serovar Typhi prevalent in Northwest Pakistan. Methodology: A total of 2,138 blood samples of suspected typhoid patients from Northwest Pakistan were collected followed by identification of Salmonella Typhi through biochemical, serological, and species-specific fliC-d gene amplification. These isolates were typed by variable-number tandem repeat (VNTR) profiling and investigated for drug resistance. Results: The overall prevalence of Salmonella Typhi was found to be 8.8% (n = 189). Thirty different VNTR strain types of Salmonella Typhi were detected and the most prevalent strain types were T1 and T4, whereas T27 was less prevalent strain. Among the 189 isolates 175 (92.5%) isolates were multidrug resistant, whereas 12 (5.8%) isolates were extensively drug resistant. Resistance to imipenem in Salmonella Typhi was not observed. Most of the isolates have genes encoding for resistance to fluoroquinolones, including gyrA (n = 164), gyrB (n = 160), parC (n = 164), parE (n = 160), ac(6')-ib-cr (n = 163), qnrS (n = 15), and qnrB (n = 3). Similarly, chloramphinicol (cat; n = 147), azithromycin (msrA; n = 3), and co-trimoxazole (dfrA7; n = 145) resistance genes were detected among Salmonella Typhi isolates. Conclusion: In this study, T1 and T4 type Salmonella Typhi strains were predominantly prevalent in Northwest Pakistan. Antibiotic resistance among Salmonella Typhi isolates were observed. Findings of the study would be helpful to devise an appropriate antibiotic policy to control the emergence of drug-resistant Salmonella Typhi in Pakistan.

Ancient DNA Study in Medieval Europeans Shows an Association Between HLA-DRB1*03 and Paratyphoid Fever

Outbreaks of infectious diseases repeatedly affected medieval Europe, leaving behind a large number of dead often inhumed in mass graves. Human remains interred in two burial pits from 14^th century CE Germany exhibited molecular evidence of Salmonella enterica Paratyphi C (S. Paratyphi C) infection. The pathogen is responsible for paratyphoid fever, which was likely the cause of death for the buried individuals. This finding presented the unique opportunity to conduct a paratyphoid fever association study in a European population. We focused on HLA-DRB1*03:01 that is a known risk allele for enteric fever in present-day South Asians. We generated HLA profiles for 29 medieval S. Paratyphi C cases and 24 contemporaneous controls and compared these to a modern German population. The frequency of the risk allele was higher in the medieval cases (29.6%) compared to the contemporaneous controls (13%; p = 0.189), albeit not significantly so, possibly because of small sample sizes. Indeed, in comparison with the modern controls (n = 39,689; 10.2%; p = 0.005) the frequency difference became statistically significant. This comparison also suggested a slight decrease in the allele’s prevalence between the medieval and modern controls. Up to now, this is the first study on the genetic predisposition to Salmonella infection in Europeans and the only association analysis on paratyphoid fever C. Functional investigation using computational binding prediction between HLA variants and S. Paratyphi and S. Typhi peptides supported a reduced recognition capacity of bacterial proteins by DRB1*03:01 relative to other common DRB1 variants. This pattern could potentially explain the disease association. Our results suggest a slightly reduced predisposition to paratyphoid fever in modern Europeans. The causative allele, however, is still common today, which can be explained by a trade-off, as DRB1*03:01 is protective against infectious respiratory diseases such as severe respiratory syndrome (SARS). It is thus possible that the allele also provided resistance to corona-like viruses in the past.

Surface-enhanced Raman spectroscopy for comparison of serum samples of typhoid and tuberculosis patients of different stages

BACKGROUND

Surface-enhanced Raman spectroscopy (SERS) is a reliable tool for the identification and differentiation of two different human pathological conditions sharing the same symptomology, typhoid and tuberculosis (TB).

OBJECTIVES

To explore the potential of surface-enhanced Raman spectroscopy for differentiation of two different diseases showing the same symptoms and analysis by principal component analysis (PCA) and partial least square discriminate analysis (PLS-DA).

METHODS

Serum samples of clinically diagnosed typhoid and tuberculosis infected individuals were analyzed and differentiated by SERS using silver nanoparticles (Ag NPs) as a SERS substrate. For this purpose, the collected serum samples were analyzed under the SERS instrument and unique SERS spectra of typhoid and tuberculosis were compared showing notable spectral differences in protein, lipid and carbohydrates features. Different stages of the diseased class of typhoid (Early acute and late acute stage) and tuberculosis (Pulmonary and extra-pulmonary stage) were compared with each other and with healthy human serum samples, which were significantly separated. Moreover, SERS data was analyzed using multivariate data analysis techniques including principal component analysis (PCA) and partial least square discriminate analysis (PLS-DA) and differences were so prominent to observe.

RESULTS

SERS Spectral data of typhoid and tuberculosis showed clear differences and were significantly separated using PCA. SERS spectral data of both stages of typhoid and tuberculosis were separated according to 1st principle component. Moreover, by analyzing data using partial least square discriminate analysis, differentiation of two disease classes were considered more valid with a 100% value of sensitivity, specificity and accuracy.

CONCLUSION

SERS can be employed for identification and comparison of two different human pathological conditions sharing same symptomology.

Overcoming reduced antibiotic susceptibility in intracellular Salmonella enterica serovar Typhimurium using AR-12

Host-directed therapies (HDTs) could enhance the activity of traditional antibiotics. AR-12 is a promising HDT against intracellular pathogens including Salmonella enterica serovar Typhimurium, and has been shown to act through modulation of autophagy and the Akt kinase pathway. Since AR-12 does not inhibit the growth of planktonic bacteria but only works in conjunction with the infected host-cell, we hypothesized that AR-12 could enhance the activity of antibiotics in less-susceptible strains in the intracellular host environment. We found that repetitive passaging of S. typhimurium in macrophages in the absence of antibiotics led to a 4-fold reduction in their intracellular susceptibility to streptomycin (STR), but had no effect on the bacteria's sensitivity to AR-12. Moreover, when the host-passaged strains were treated with a combined therapy of AR-12 and STR, there was a significant reduction of intracellular bacterial burden compared to STR monotherapy. Additionally, co-treatment of macrophages infected with multi-drug resistant S. typhimurium with AR-12 and STR or ampicillin showed enhanced clearance of the intracellular bacteria. The drug combination did not elicit this effect on planktonic bacteria. Overall, AR-12 enhanced the clearance of less susceptible S. typhimurium in an intracellular environment.

Antibiotic resistome of Salmonella typhi: molecular determinants for the emergence of drug resistance

Resistome is a cluster of microbial genes encoding proteins with necessary functions to resist the action of antibiotics. Resistome governs essential and separate biological functions to develop resistance against antibiotics. The widespread clinical and nonclinical uses of antibiotics over the years have combined to select antibiotic-resistant determinants and develop resistome in bacteria. At present, the emergence of drug resistance because of resistome is a significant problem faced by clinicians for the treatment of Salmonella infection. Antibiotic resistome is a dynamic and ever-expanding component in Salmonella. The foundation of resistome in Salmonella is laid long before; therefore, the antibiotic resistome of Salmonella is reviewed, discussed, and summarized. We have searched the literature using PubMed, MEDLINE, and Google Scholar with related key terms (resistome, Salmonella, antibiotics, drug resistance) and prepared this review. In this review, we summarize the status of resistance against antibiotics in S. typhi, highlight the seminal work in the resistome of S. typhi and the genes involved in the antibiotic resistance, and discuss the various methods to identify S. typhi resistome for the proactive identification of this infection and quick diagnosis of the disease.

Antibacterial activity of Citrus hystrix toward Salmonella spp. infection

INTRODUCTION

Citrus hystrix is widely used by Indonesians as a traditional medicine for gastrointestinal diseases, including Salmonella spp. infection. We investigated the antibacterial activity of the ethanolic peel extract of C. hystrix against Salmonella typhimurium.

METHODS

The antibacterial activity was evaluated both in vitro and in vivo. The minimum inhibitory concentration (MIC) of the extract was determined at a concentration of 0.625% by agar dilution assay. Later, the in vivo antibacterial activity was examined by the administration of 16mg of the extract daily for three consecutive days in a mouse model infected with S. typhimurium.

RESULTS

The bacterial loads of S. typhimurium in the ileum, liver, and spleen decreased after 24h of administration of the extract (p=0.00008, p=0.00084, and p=0.00003, respectively).

CONCLUSION

The ethanolic peel extract of C. hystrix shows antibacterial activity against S. typhimurium, indicating the potential of C. hystrix as an effective treatment for Salmonella spp. infection.

Mechanisms of typhoid toxin neutralization by antibodies targeting glycan receptor binding and nuclease subunits

Nearly all clinical isolates of Salmonella Typhi, the cause of typhoid fever, are antibiotic resistant. All S. Typhi isolates secrete an A2B5 exotoxin called typhoid toxin to benefit the pathogen during infection. Here, we demonstrate that antibiotic-resistant S. Typhi secretes typhoid toxin continuously during infection regardless of antibiotic treatment. We characterize typhoid toxin antibodies targeting glycan-receptor-binding PltB or nuclease CdtB, which neutralize typhoid toxin in vitro and in vivo, as demonstrated by using typhoid toxin secreted by antibiotic-resistant S. Typhi during human cell infection and lethal dose typhoid toxin challenge to mice. TyTx11 generated in this study neutralizes typhoid toxin effectively, comparable to TyTx4 that binds to all PltB subunits available per holotoxin. Cryoelectron microscopy explains that the binding of TyTx11 to CdtB makes this subunit inactive through CdtB catalytic-site conformational change. The identified toxin-neutralizing epitopes are conserved across all S. Typhi clinical isolates, offering critical insights into typhoid toxin-neutralizing strategies.

A global resource for genomic predictions of antimicrobial resistance and surveillance of Salmonella Typhi at pathogenwatch

As whole-genome sequencing capacity becomes increasingly decentralized, there is a growing opportunity for collaboration and the sharing of surveillance data within and between countries to inform typhoid control policies. This vision requires free, community-driven tools that facilitate access to genomic data for public health on a global scale. Here we present the Pathogenwatch scheme for Salmonella enterica serovar Typhi (S. Typhi), a web application enabling the rapid identification of genomic markers of antimicrobial resistance (AMR) and contextualization with public genomic data. We show that the clustering of S. Typhi genomes in Pathogenwatch is comparable to established bioinformatics methods, and that genomic predictions of AMR are highly concordant with phenotypic susceptibility data. We demonstrate the public health utility of Pathogenwatch with examples selected from >4,300 public genomes available in the application. Pathogenwatch provides an intuitive entry point to monitor of the emergence and spread of S. Typhi high risk clones.

Whole genome sequencing data are increasingly becoming routinely available but generating actionable insights is challenging. Here, the authors describe Pathogenwatch, a web tool for genomic surveillance of S. Typhi, and demonstrate its use for antimicrobial resistance assignment and strain risk assessment.

Exposure to Anthropogenic Areas May Influence Colonization by Zoonotic Microorganisms in Scavenging Birds

Wild bird species have commonly been implicated as potential vectors of pathogens to other species, humans included. However, the habitat where birds live could influence the probability to acquire these pathogens. Here, we evaluated if the characteristics of the environment used by obligate scavenging birds (vultures) influence their colonization by zoonotic pathogens. For this, we particularly focused on Salmonella spp., a zoonotic pathogen commonly present in bird species. The occurrence of this bacteria was evaluated in free ranging Andean condors (Vultur gryphus) using natural environments from Argentina and compared with those obtained from condors under human care. In addition, we compared our results with those reported for other wild vultures using natural and anthropized environments at a global scale. We did not find Salmonella spp. in samples of wild condors. Captive condor samples presented Salmonella spp. with an occurrence of 2.8%, and one isolate of Meticilin Resistant Staphylococcus aureus, among other potential pathogenic microorganisms. Moreover, some species of free ranging vultures from diverse geographical areas using anthropized environments tend to present higher occurrences of Salmonella spp. These results highlight the importance of pristine ecosystems to protect vultures' health toward pathogenic microorganisms that can produce disease in these birds, but also in other species. We call for more studies evaluating differences in occurrence of zoonotic pathogens in vultures according to the quality of the environment they use. Even when vultures have not been implicated in zoonotic pathogen spread, our results add information to evaluate potential events of pathogen spillover between vultures and from these birds to other species.

Phylogenetic Analysis Indicates a Longer Term Presence of the Globally Distributed H58 Haplotype of Salmonella Typhi in Southern India

Background

Typhoid fever caused by Salmonella Typhi is a major public health concern in low-/middle-income countries. A recent study of 1900 global S. Typhi indicated that South Asia might be the site of the original emergence of the most successful and hypervirulent clone belonging to the 4.3.1 genotype. However, this study had limited samples from India.

Methods

We analyzed 194 clinical S. Typhi, temporal representatives from those isolated from blood and bone marrow cultures in southern India, over 26 years (1991–2016). Antimicrobial resistance (AMR) testing was performed for most common clinical agents. Whole-genome sequencing and SNP-level analysis was conducted. Comparative genomics of Vellore isolates was performed to infer transmission and AMR events.

Results

We identified multidrug-resistance (MDR)–associated clade 4.3.1 as the dominant genotype. We detected 4.3.1 S. Typhi as early as 1991, the earliest to be reported form India, and the majority were fluoroquinolone resistant and not MDR. MDR was not detected at all in other genotypes circulating in Vellore. Comparison with global S. Typhi showed 2 Vellore subgroups (I and II) that were phylogenetically highly related to previously described South Asia (subgroup I, II) and Southeast Asia (subgroup II) clades.

Conclusions

4.3.1 S. Typhi has dominated in Vellore for 2 decades. Our study would assist public health agencies in better tracking of transmission and persistence of this successful clade in India and globally. It informs clinicians of the AMR pattern of circulating clone, which would add confidence to their prophylactic/treatment decision making and facilitate efficient patient care.

The Effect of Acute and Chronic Infection-Induced by AvrA Protein of Salmonella typhimurium on Radical Oxygen Species, Phosphatase and Tensin Homolog, and Cellular Homolog Expression During the Development of Colon Cancer

AIM. The aim of the study was to analyze Avra's effector in inducing cancer stem cells into colon cancer through increased radical oxygen species (ROS), PTEN expression and c-myC as markers of tumorigenesis in mice model of the colorectal cancer infected with S. typhimurium. METHODS. The study used balb c mice induced once a week by 10 mg / mL / day of AOM for 1-week and 12-week treatment period. Isolation of S. typhimurium specific protein had been carried out before being induced to mice in intraperitoneal manner in the amount of 40 mL / 50 mL. Propagation of S. typhimurium ATCC bacteria with MacConkey media and isolation of S. typhimurium protein were administered. The sample was divided into 4 groups, positive control group (group that was only exposed to azoxymethane (AOM), group exposed to both AOM and AvrA (AOM + AvrA), and group exposed to both AOM and S. typhimurium (AOM + S. typhimurium). Blood flow cytometry and soft tissue sampling for IHC and data analysis were then conducted. RESULTS. The results of the study showed that there was an increase in the expression of ROS, PTEN and c-Myc. Increased ROS expression was found in the 12-week treatment period group and it was known that such increase was due to AOM + S. typhimurium (45.78 ± 2.93) induction compared to AOM, AOM + AvrA and control (p <0.05). PTEN and C-myc expression increased at the 12th week compared to the negative control. CONCLUSION. Inflammation is the triggering factor for colorectal cancer, in which the expression of ROS, PTEN and c-Myc as the colorectal cancer markers increases in both the acute and chronic phases.

Antimicrobial Susceptibility Pattern of Salmonella spp. Isolated from Enteric Fever Patients in Nepal

INTRODUCTION

Enteric fever, a systemic infection caused by Salmonella enterica Typhi and S. enterica Paratyphi is one of the most common infections in developing countries such as Nepal. Aside from irrational practices of antibiotic use, mutations in chromosomal genes encoding DNA gyrase and Topoisomerase IV and by plasmid mediated quinolone resistant (PMQR) genes are suggested mechanisms for the development of resistance to nalidixic acid and reduced susceptibility to ciprofloxacin. Regardless of high endemicity of enteric fever in Nepal, there is paucity of studies on prevalence and drug-resistance of the pathogen. Therefore, this study aimed to assess the antibiotic susceptibility pattern of Salmonella isolates and determine the minimum inhibitory concentration of ciprofloxacin.

METHODS

A total of 1298 blood samples were obtained from patients with suspected enteric fever, attending Sukraraj Tropical and Infectious Disease Hospital (STIDH) during March-August, 2019. Blood samples were inoculated immediately into BACTEC culture bottles and further processed for isolation and identification of Salmonella Typhi and S. Paratyphi. Axenic cultures of the isolates were further subjected to antimicrobial susceptibility testing (AST) by using the modified Kirby-Bauer disc diffusion method based on the guidelines by CLSI. The minimum inhibitory concentration (MIC) of ciprofloxacin was determined by agar-dilution method.

RESULTS

Out of 1298 blood cultures, 40 (3.1%) were positive for Salmonella spp. among which 29 (72.5%) isolates were S. Typhi and 11 (27.5%) isolates were S. Paratyphi A. In AST, 12.5% (5/40), 15% (6/40) and 20% (8/40) of the Salmonella isolates were susceptible to nalidixic acid, ofloxacin and levofloxacin, respectively, whereas none of the isolates were susceptible to ciprofloxacin. The MIC value for ciprofloxacin ranged from 0.06-16 µg/mL in which, respectively, 5% (2/40) and 52.5% (21/40) of the isolates were susceptible and resistant to ciprofloxacin. None of the isolates showed multidrug-resistance (MDR) in this study.

CONCLUSION

This study showed high prevalence of quinolone-resistant Salmonella spp., while there was marked re-emergence of susceptibilities to traditional first option drugs. Hence, conventional first-line-drugs and third-generation cephalosporins may find potential usage as the empirical drugs for enteric fever. Although our reporting was free of MDR strains, extensive surveillance, augmentation of diagnostic facilities and treatment protocol aided by AST report are recommended for addressing the escalating drug-resistance in the country.

Mass burial genomics reveals outbreak of enteric paratyphoid fever in the Late Medieval trade city Lübeck

Medieval Europe was repeatedly affected by outbreaks of infectious diseases, some of which reached epidemic proportions. A Late Medieval mass burial next to the Heiligen-Geist-Hospital in Lübeck (present-day Germany) contained the skeletal remains of more than 800 individuals who had presumably died from infectious disease. From 92 individuals, we screened the ancient DNA extracts for the presence of pathogens to determine the cause of death. Metagenomic analysis revealed evidence of Salmonella enterica subsp. enterica serovar Paratyphi C, suggesting an outbreak of enteric paratyphoid fever. Three reconstructed S. Paratyphi C genomes showed close similarity to a strain from Norway (1200 CE). Radiocarbon dates placed the disease outbreak in Lübeck between 1270 and 1400 cal CE, with historical records indicating 1367 CE as the most probable year. The deceased were of northern and eastern European descent, confirming Lübeck as an important trading center of the Hanseatic League in the Baltic region.

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Salmonella enterica Paratyphi C detected in remains from a mass burial in Lübeck

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Outbreak of enteric paratyphoid fever likely occurred in 1367 CE

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Pathogen genomes showed close similarity to a strain from Norway (1200 CE)

Salmonella Typhi and Salmonella Paratyphi prevalence, antimicrobial susceptibility profile and factors associated with enteric fever infection in Bahir Dar, Ethiopia

Enteric fever (EF) is caused by Salmonella enterica serovars Typhi (S. Typhi) and Paratyphi (S. Paratyphi) causing significant health problems in developing countries including Ethiopia. Thus present study aimed to determine prevalence and antimicrobial resistance profile of S. Typhi and S. Paratyphi among EF suspected patients at Felege-Hiwot comprehensive specialized hospital, Bahir Dar, Ethiopia. Hospital based cross-sectional study was conducted from March-to-May 2020. Totally, 150 patients were included conveniently. Data were collected using questionnaires by face-to-face interview. Concurrently, venous blood and stool specimens were collected and processed following standard bacteriological technique. Antimicrobial susceptibility test (AST) was performed by disc diffusion method. Logistic regression was performed to identify factors associated with EF infection. The study indicated 5.3% EF prevalence where S. Typhi accounted 75%. S. Typhi and S. Paratyphi isolates were 100% sensitive to cephalosporins but at least 83.3% showed resistance against chloramphenicol and tetracycline. At least 66.7% of isolates were multidrug resistance (MDR). Using well water for drinking (AOR = 6.22, CI 1.4-27.5) and previous EF history (AOR = 10.74, CI 2.01-55.9) were significantly associated with EF infection. Thus high bacterial prevalence and MDR isolates was observed. Therefore, health professionals should consider AST and use antibiotics with cautions for EF patient management.

Effects of Curcumin and Silymarin on the Shigella dysenteriae and Campylobacter jejuni In vitro

OBJECTIVE

Antimicrobial properties of silymarin and curcumin have been assessed against several infectious agents. The aim of this study was to investigate the anti-apoptotic and antibacterial effects of both compounds on the expression of genes among Shigella dysenteriae ATCC 12022 and Campylobacter jejuni subsp. jejuni strain ATCC 33560 standard strains.

METHODS

S. dysenteriae and C. jejuni standard strains were prepared from reference laboratory. Additionally, two clinical multidrug-resistant (MDR) isolates were adopted. Silymarin and curcumin stocks were purchased from Sigma Corporation (USA), and after preparation of dilutions (0.5-512 μg/ml), the minimum inhibitory concentration (MIC) and minimum bactericidal concentrations (MBC) were determined. Furthermore, the effect of 100 μg/ml of each compound was also evaluated on the expression of two gyrB and 16S rRNA housekeeping genes by quantitative real-time PCR (qRT-PCR).

RESULTS

Silymarin MIC and MBC were 512 μg/ml and > 512 μg/ml against S. dysenteriae and > 512μg/ml against C. jejuni standard strains, respectively. Moreover, curcumin MIC and MBC concentrations were 256 μg/ml and 512 μg/ml, respectively for ATCC strains. Silymarin down-expressed the expression of gyrB gene in S. dysenteriae and gyrB and 16srRNA gene in C. jejuni significantly (p < 0.05) compared with unexposed strains. In addition, curcumin could down-express the both gyrB and 16S rRNA genes in both strains significantly (p < 0.05). For two MDR clinical isolates, both MIC and MBC of compounds were > 512 μg/ml. Addition of 100 μg/ml curcumin and silymarin to ampicillin (10 μg/ml) lowered the MIC of MDR S. dysenteriae to 256 μg/ml and 512 μg/ml, respectively. However, no MIC change was observed with regard to C. jejuni.

CONCLUSION

In this study, curcumin and silymarin could inhibit the growth of S. dysenteriae and C. jejuni and 100 μg/ml sub-MIC levels exhibited the suppression of housekeeping genes. Combating pathogenic bacteria by compounds alternative to antibiotics in the era of antibiotic resistance is a proper strategy, though more studies using combinations of them are needed.

Geographical distribution of Typhoid using Geographic Information System (GIS) during 2009-2014 in Iran

Background: Salmonella induced infections remain one of the most important health problems worldwide. The purpose of this study is to investigate the incidence and geographical distribution of typhoid using GIS and to predict its incidence in Iran in 2021.

Methods: This study is a descriptive analytical study. Information on pertussis was obtained from the Center for Communicable Diseases Control during 2009-2015. In the next step, ArcGIS 9.3 was used to prepare geographic maps of the disease incidence and frequency Therefore, using the Raster Calculator tool, the disease prediction map was drawn.

Results: The results showed that the highest incidence of typhoid during 2009-2014 was in Kermanshah, Lorestan, Hamadan, Kurdistan, and Ilam provinces. The incidence of typhoid in Iran increased during 2009-2010. The annual incidence of typhoid decreased from 0.85 per 100,000 in 2010 to 0.5 in 2014. Based on the modeling results for Iran, Kermanshah, Lorestan, Kurdistan, Ilam and Hamadan provinces with 92.17%, 46.56%, 31.74%, 25.62% and 22.96% of their areas (Km2) are at high risk for typhoid in the coming years, respectively.

Conclusion: Considering that the provinces of Kermanshah, Lorestan, Kurdistan, Ilam, and Hamadan are at risk of typhoid incidence in the coming years in Iran, and given that salmonella infections have a direct relationship with the individual’s health status and individual’s environmental health and socioeconomic status, improving the health status and disease control in carriers as well as improving the socio-economic status of the population living in these areas can prevent the disease in the years to come.

Water Quality and Life Expectancy: Parallel Courses in Time

Since ancient times, the need for healthy water has resulted in the development of various kinds of water supply systems. From early history, civilizations have developed water purification devices and treatment methods. The necessity for fresh water has influenced individual lives as well as communities and societies. During the last two hundred years, intensive and effective efforts have been made internationally for sufficient water quantity and quality. At the same time, human life expectancy has increased all over the globe at unprecedented rates. The present work represents an effort to sketch out how water purity and life expectancy have entangled, thus influencing one another. Water properties and characteristics have directly affected life quality and longevity. The dramatic increase in life expectancy has been, indisputably, affected by the improvement in water quality, but also in other concomitant factors, varying temporally and spatially in different parts of the world throughout the centuries. Water technologies and engineering have an unequivocal role on life expectancy. In some cases, they appear to have taken place earlier than the progress of modern medicine. Among these, improved sanitation, personal hygiene, progress in medicine, and better standards of economic living have played the greatest roles.

ESBL-producing strains isolated from imported cases of enteric fever in England and Wales reveal multiple chromosomal integrations of blaCTX-M-15 in XDR Salmonella Typhi

Background

There are approximately 300 cases of enteric fever reported annually from England and Wales; most are imported infections. Clinical management of enteric fever remains a challenge with the emergence of ESBL-producing strains, especially XDR Salmonella Typhi from Sindh, Pakistan.

Methods

All strains of S. Typhi and Salmonella Paratyphi A isolated from cases presenting with symptoms of enteric fever in England and Wales, between 1 April 2014 and 31 March 2020, were characterized using WGS. Antibiotic susceptibility testing was performed using an agar dilution method.

Results

ESBL strains contributed to 69 cases of enteric fever (S. Typhi n = 68, S. Paratyphi A n = 1); 68 were imported (Pakistan n = 64, Iraq n = 2, Bangladesh n = 1 and India n = 1). Ages ranged from 1 to 56 years, 36/69 (52%) were children, 52% were female and the duration of hospital stay ranged from 1 to 23 days. The ESBL phenotype was conferred by the presence of blaCTX-M-15 (S. Typhi n = 67 and S. Paratyphi A n = 1) or blaCTX-M-55 (S. Typhi n = 1). An IncY plasmid harbouring blaCTX-M-15 and qnr was detected in 56 strains from Pakistan. The IncY plasmid was absent in the remaining strains and there was evidence of a 4 kb ISEcpl-blaCTX-M-15-tnp gene cassette insertion into the chromosome at one of three integration points.

Conclusions

Chromosomal integration of blaCTX-M-15 within the XDR Sindh strains may lead to the maintenance of resistance in the absence of antibiotic selection pressure. Empirical treatment of cases of complicated enteric fever returning from Pakistan will henceforth have to include a carbapenem.

Emerging high-level ciprofloxacin-resistant Salmonella enterica serovar typhi haplotype H58 in travelers returning to the Republic of Korea from India

In Korea, typhoid fever is a rare disease due to improved living standards. However, typhoid fever remains a major burden in developing countries and regions, such as India and Southeast Asia. In this study, we isolated Salmonella Typhi (S. Typhi) from eight patients with typhoid fever who were travelers returning from India. The strains isolated were characterized by antimicrobial susceptibility profiling and whole-genome sequencing (WGS) analysis. All strains were resistant to nalidixic acid and azithromycin. Among them, four isolates were highly resistant to ciprofloxacin (MIC ≥32 μg/ml); these strains have not been confirmed in Korea PulseNet DB. According to WGS, the ciprofloxacin-resistant strains belong to the global dominant multidrug-resistant (MDR) haplotype H58 (SNP glpA C1047T, SptP protein Q185* (premature stop codon)) and do not harbor the MDR plasmid. H58-associated SNPs in membrane and metabolism genes, including yhdA, yajI, hyaE, tryE, rlpB and metH, are present. Additionally, phylogenetic analysis assigned the H58 strains to sublineage II, whereas the non-H58 strains are closely related to haplotype H50. The presence of high-level ciprofloxacin-resistant S. Typhi haplotype H58 in Korea was first confirmed as due to influx from overseas via travelers. This study provides information about intercontinental drug-resistant transmission between countries and suggests that travelers need to be careful about personal hygiene.

Typhoid fever is a systemic human disease that involves gastroenteritis, fever, and severe diarrhea caused by Salmonella enterica serotype Typhi (S. Typhi) and requires prompt antibiotic treatment. Due to improved living standards, it has become a rare disease but is still prevalent in developing countries such as India and Southeast Asia. Most reported cases are related to travelers or immigrants from these regions. Because of treatment failure, serious morbidity, and economic loss, there is a global health issue with the emergence of antimicrobial-resistant strains associated with fluoroquinolones and third-generation cephalosporins. Of antimicrobial-resistant S. Typhi, haplotype H58 is a dominant multidrug-resistant lineage that has been reported in endemic regions over the past two decades. We identified fluoroquinolone resistance in cases of S. Typhi infection after travel to India. Among them, some strains highly resistant to ciprofloxacin were confirmed to have characteristics of haplotype H58. In Korea, S. Typhi haplotype H58 from travelers has not been confirmed before. This study provides information about intercontinental drug-resistant transmission between countries and suggests that travelers need to be careful about personal hygiene.

One-step differential detection of Salmonella enterica serovar Typhi, serovar Paratyphi A and other Salmonella spp. by using a quadruplex real-time PCR assay

Diseases caused by typhoidal and non-typhoidal Salmonella remain a considerable threat to both developed and developing countries. Based on the clinical symptoms and serological tests, it is sometimes difficult to differentiate the Salmonella enterica serovar Paratyphi A (S. enterica serovar Paratyphi A) from serovar Typhi (S. enterica serovar Typhi). In this study, we developed a quadruplex real-time polymerase chain reaction (PCR) assay with an internal amplification control (IAC), to simultaneously differentiate S. enterica serovar Paratyphi A from serovar Typhi and to detect other Salmonella serovars which cause salmonellosis in humans. This assay was evaluated on 155 salmonellae and non-salmonellae strains and demonstrated 100% specificity in species differentiation. Inclusion of an IAC did not affect the efficiency of the assay. Further evaluation using a blind test on spiked stool, blood and food specimens showed that the detection limit was at 10³ -10⁴ CFU/mL (or g) and a high PCR efficiency with different targets (R² > 0.99), except for S. enterica serovar Paratyphi A in blood. This assay has been applied to clinical specimens to detect the causative agents of gastrointestinal infections and has successfully identified 6 salmonellosis patients from the 50 diarrhoea patients. The quadruplex real-time PCR developed in this study could enhance the detection and differentiation of salmonellae. This assay could be applied to stools, blood and food based on the notable performance in the simulation tests and field evaluation.

The low level of O antigen in Salmonella enterica Paratyphi A is due to inefficiency of the glycosyltransferase WbaV

The group A O antigen is the major surface polysaccharide of Salmonella enterica serovar Paratyphi A (SPA), and the focal point for most current vaccine development efforts. The SPA O-antigen repeat (O unit) is structurally similar to the group D1 O unit of S. enterica serovar Typhi, differing only in the presence of a terminal side-branch paratose (Par) in place of tyvelose (Tyv), both of which are attached by the glycosyltransferase WbaV. The two O-antigen gene clusters are also highly similar, but with a loss-of-function mutation in the group A tyv gene and the tandem amplification of wbaV in most SPA strains. In this study, we show that SPA strains consistently produce less O antigen than their group D1 counterparts and use an artificial group A strain (D1 Δtyv) to show this is due to inefficient Par attachment by WbaV. We also demonstrate that group A O-antigen production can be increased by overexpression of the wbaV gene in both the D1 Δtyv strain and two multi-wbaV SPA strains. These findings should be broadly applicable in ongoing vaccine development pipelines, where efficient isolation and purification of large quantities of O antigen is of critical importance.

Enhanced biofilm and extracellular matrix production by chronic carriage versus acute isolates of Salmonella Typhi

Salmonella Typhi is the primary causative agent of typhoid fever; an acute systemic infection that leads to chronic carriage in 3–5% of individuals. Chronic carriers are asymptomatic, difficult to treat and serve as reservoirs for typhoid outbreaks. Understanding the factors that contribute to chronic carriage is key to development of novel therapies to effectively resolve typhoid fever. Herein, although we observed no distinct clustering of chronic carriage isolates via phylogenetic analysis, we demonstrated that chronic isolates were phenotypically distinct from acute infection isolates. Chronic carriage isolates formed significantly thicker biofilms with greater biomass that correlated with significantly higher relative levels of extracellular DNA (eDNA) and DNABII proteins than biofilms formed by acute infection isolates. Importantly, extracellular DNABII proteins include integration host factor (IHF) and histone-like protein (HU) that are critical to the structural integrity of bacterial biofilms. In this study, we demonstrated that the biofilm formed by a chronic carriage isolate in vitro, was susceptible to disruption by a specific antibody against DNABII proteins, a successful first step in the development of a therapeutic to resolve chronic carriage.

Salmonella Typhi, a human restricted pathogen is the primary etiologic agent of typhoid fever, an acute systemic infection that has a global incidence of 21 million cases annually. Although the acute infection is resolved by antibiotics, 3–5% of individuals develop chronic carriage that is difficult to resolve with antibiotics. A majority of these indivuals serve as reservoirs for further spread of the disease. Understanding the differences between acute and chronic carrier strains is key to design novel targeted approaches to undermine carriage. Here, we demonstrated that chronic carrier strains although not genotypically distinct from acute strains, formed thicker biofilms with greater relative levels of extracellular eDNA and DNABII proteins than those formed by acute infection isolates. We also demonstrated that an antibody against DNABII proteins significantly disrupted biofilms formed by a chronic carrier strain and therefore supported development of therapeutic use of this antibody to attenuate chronic carriage.

Correlation Between Pathogenic Determinants Associated with Clinically Isolated Non-Typhoidal Salmonella

Non-typhoidal and Typhoidal Salmonella are bacterial pathogens source of worldwide and major disease burden. Virulent determinants of specific serovars belonging to non-typhoidal Salmonella have been extensively studied in different models, yet the pathogenesis of this group of bacteria and the development of clinical symptoms globally remains underexplored. Herein, we implemented microbiological and molecular procedures to investigate isolate virulence traits and molecular diversity, likely in association with disease severity. Our results show that selected clinical isolates from a tertiary referring hospital, depending on the richness of the environment and isolate serotypes, exhibited different, and sometimes controversial, virulence properties. The tested strains were susceptible to Ceftriaxone (90%) with decreasing reactivity to Trimethoprim–Sulfamethoxazole (72%), Chloramphenicol (64%), Ampicillin (48%), Gentamicin (44%), and Ciprofloxacin (2%). Disc susceptibility results partially correlated with minimum inhibitory concentration (MIC); however, special attention must be given to antimicrobial treatment, as a rise in multi-resistant isolates to Trimethoprim–Sulfamethoxazole (2/38 µg/mL), Minocycline (8 µg/mL) and Ampicillin (16 µg/mL) has been noticed, with two isolates resistant to Ceftazidime (16 µg/mL). By comparison to previous molecular epidemiology studies, the variation in the gene profiles of endemic pathogens supports the need for continuous and up-to-date microbiological and molecular reports.

Downregulation of a novel flagellar synthesis regulator AsiR promotes intracellular replication and systemic pathogenicity of Salmonella typhimurium

The intracellular pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) exploits host macrophage as a crucial survival and replicative niche. To minimize host immune response stimulated by flagellin, the expression of flagellar genes is downregulated during S. Typhimurium growth within host macrophages. However, the underlying mechanisms are largely unknown. In this study, we show that STM14_1285 (named AsiR), a putative RpiR-family transcriptional regulator, which is downregulated within macrophages as previously reported and also confirmed here, positively regulates the expression of flagellar genes by directly binding to the promoter of flhDC. By generating an asiR mutant strain and a strain that persistently expresses asiR gene within macrophages, we confirmed that the downregulation of asiR contributes positively to S. Typhimurium replication in macrophages and systemic infection in mice, which could be attributed to decreased flagellar gene expression and therefore reduced flagellin-stimulated secretion of pro-inflammatory cytokines IL-1β and TNF-α. Furthermore, the acidic pH in macrophages is identified as a signal for the downregulation of asiR and therefore flagellar genes. Collectively, our results reveal a novel acidic pH signal-mediated regulatory pathway that is utilized by S. Typhimurium to promote intracellular replication and systemic pathogenesis by repressing flagellar gene expression.

The Majority of Typhoid Toxin-Positive Salmonella Serovars Encode ArtB, an Alternate Binding Subunit

While previous reports had suggested that the typhoid toxin (TT) could potentially use ArtB as an alternate binding subunit, this was thought to play a minor role in the evolution and biology of the toxin. In this study, we establish that both TT genes and artB are widespread among Salmonella enterica subsp. enterica, suggesting that TT likely plays a broader role in Salmonella virulence that extends beyond its proposed role in typhoid fever.

Salmonella enterica encodes a wide array of virulence factors. One novel virulence factor, an A₂B₅ toxin known as the typhoid toxin (TT), was recently identified among a variety of S. enterica serovars. While past studies have shown that some serovars encode both the TT (active subunits CdtB and PltA and binding subunit PltB) and a second binding subunit (ArtB), these serovars were thought to be the exception. Here, we show that genes encoding the TT are detected in more than 100 serovars representing distinct phylogenetic lineages of S. enterica subsp. enterica, although clade B and section Typhi are significantly more likely to encode TT genes than serovars from other clades. Furthermore, we show that 81% of these TT-positive serovars also encode artB, suggesting that the cooccurrence of both toxin binding subunits is considerably more common than previously thought. A combination of in silico modeling, bacterial two-hybrid system screening, and tandem affinity purification (TAP) of toxin subunits suggests that ArtB and PltB interact in vitro, at least under some growth conditions. While different growth conditions yielded slightly higher transcript abundances of artB and pltB, both genes had their highest relative transcript abundances when Salmonella was grown under low-Mg²⁺ conditions, suggesting that ArtB and PltB may compete for inclusion in the TT. Together, our results suggest that ArtB likely plays an important and previously underappreciated role in the biology of the TT produced by typhoidal and nontyphoidal Salmonella.

IMPORTANCE While previous reports had suggested that the typhoid toxin (TT) could potentially use ArtB as an alternate binding subunit, this was thought to play a minor role in the evolution and biology of the toxin. In this study, we establish that both TT genes and artB are widespread among Salmonella enterica subsp. enterica, suggesting that TT likely plays a broader role in Salmonella virulence that extends beyond its proposed role in typhoid fever. Furthermore, our data suggest the selective maintenance of both toxin binding subunits, which may compete for inclusion in the holotoxin. Last, our data support the importance of characterizing diverse nontyphoidal Salmonella (NTS) serovars, as the presence of classically defined typhoidal virulence factors among NTS serovars continues to challenge the typhoid-nontyphoid Salmonella paradigm.

Perspectives for the use of latex peptidases from Calotropis procera for control of inflammation derived from Salmonella infections

BACKGROUND

Anti-inflammatory properties have been attributed to latex proteins of the medicinal plant Calotropis procera.

PURPOSE

A mixture of cysteine peptidases (LPp2) from C. procera latex was investigated for control of inflammatory mediators and inflammation in a mouse model of Salmonella infection.

METHODS

LPp2 peptidase activity was confirmed by the BANA assay. Cytotoxicity assays were conducted with immortalized macrophages. Peritoneal macrophages (pMØ) from Swiss mice were stimulated with lipopolysaccharide (LPS) in 96-well plates and then cultured with nontoxic concentrations of LPp2. Swiss mice intravenously received LPp2 (10 mg/kg) and then were challenged intraperitoneally with virulent Salmonella enterica Ser. Typhimurium.

RESULTS

LPp2 was not toxic at dosages lower than 62.2 μg/mL. LPp2 treatments of pMØ stimulated with LPS impaired mRNA expression of pro-inflammatory cytokines IL-1β, TNF-α, IL-6 and IL-10. LPp2 increased the intracellular bacterial killing in infected pMØ. Mice given LPp2 had a lower number of leukocytes in the peritoneal cavity in comparison to control groups 6 h after infection. The bacterial burden and histological damage were widespread in target organs of mice receiving LPp2.

CONCLUSION

We conclude that LPp2 contains peptidases with strong anti-inflammatory properties, which may render mice more susceptible to early disseminated infection caused by Salmonella.

Isolation and Evaluation of Probiotic Potential of Lactic Acid Strains From Healthy Equines for Potential Use in Salmonella Infection

The objective of the present study was to evaluate the probiotic properties, security and antibacterial ability in vivo of isolated strains from healthy equine. In the present study, two Pediococcus acidilactici (P1 and P2) and two Lactobacillus equi (L1 and L2) were isolated. All isolates were died when exposed to pH 2.0 for 3 hours but survived at pH 3.0 and pH 4.0 with differential survival rate, and there is a higher survival rate at pH 4.0. Similarly, the isolates showed different tolerance to bile. The viable bacteria count was sustained at high levels in a tolerance test with artificial gastrointestinal fluid. The isolates survived and grew at temperatures between 37 and 55°C but died at 65°C. Four strains exhibited inhibitory activity against pathogens, including Salmonella typhimurium (CVCC542), Escherichia coli (C83902), Staphylococcus aureus (BNCC186335), and Pasteurella multocida (clinical isolate). These isolates exhibited differential antibiotic susceptibility. In safety trials, all isolates were γ-hemolytic, and the oral toxicity of strains P1 (gavaged with 1 × 109 CFU/day) and L1 (gavaged with 1 × 109 CFU/day) were analyzed in mice. There were no effects on the overall health status of mice. There were no prominent differences in the incidence of bacteria translocation to blood, liver, and spleen. Mice gavaged with Pediococcus acidilactici P1 (1 × 108 CFU/day) or Lactobacillus equi L1 (1 × 108 CFU/day) as prevention showed lower rates of diarrhea and mortality after being challenged with Salmonella typhimurium (4 × 106 CFU signal dose, 0.1 mL by intragastric gavage). The results indicate that the isolated strains could act as potential probiotics, providing a new way to reduce salmonella infection, which merit future application studies.

Highly adaptable and sensitive FRET-based aptamer assay for the detection of Salmonella paratyphi A

Here we demonstrate a facile and versatile fluorescence resonance energy transfer (FRET) based aptasensor for rapid detection of Salmonella paratyphi A. The assay shows a detection limit up to 10 cfu·mL^-1 with no cross-reactivity with other bacterial species. Less than 8% of inter-assay coefficient variance and recovery rate between 85 and 102% attests the assay reliability. The advantages of FRET-based aptamer assay over the conventional immunoassay formats such as ELISA are the specificity, speed, reliability, and simplicity of the assay. The ssDNA aptamers specific towards pathogenic Salmonella paratyphi A were generated via whole-cell SELEX. The aptamer was conjugated onto quantum dot (QD) that served as the molecular beacon and graphene oxide (GO) was used as a fluorescence quencher. Thus the proposed method enables detection of target pathogen using FRET-based assay. Further interaction of aptamer with pathogen protein DNA gyrase was explored using classical molecular dynamics simulation.

Syntheses of Salmonella Paratyphi A Associated Oligosaccharide Antigens and Development towards Anti-Paratyphoid Fever Vaccines

With the emergence of multidrug resistant Salmonella strains, the development of anti-Salmonella vaccines is an important task. Currently there are no approved vaccines against Salmonella Paratyphi A, the leading cause of paratyphoid fever. To fill this gap, oligosaccharides corresponding to the O-polysaccharide repeating units from the surface of Salmonella Paratyphi A have been synthesized through convergent stereoselective glycosylations. The synthetic glycan antigen was conjugated with a powerful immunogenic carrier system, the bacteriophage Qβ. The resulting construct was able to elicit strong and long-lasting anti-glycan IgG antibody responses, which were highly selective toward Salmonella Paratyphi A associated glycans. The availability of well-defined glycan antigen enabled the determination that one repeating unit of the polysaccharide is sufficient to induce protective antibodies, and the paratose residue and/or the O-acetyl modifications on the backbone are important for recognition by antibodies elicited by a Qβ-tetrasaccharide conjugate. Immune sera provided excellent protection to mice from lethal challenge with Salmonella Paratyphi A, highlighting the potential of the synthetic glycan-based vaccine.

Predictive evaluation of pediatric patients based on their typhoid fever status using linear discriminant model

Epidemiologic studies have established a relationship between pediatric patients and typhoid fever infection. This study was carried out to ascertain if specific hematological measurements of the pediatric patients discriminate between their positive and negative status to typhoid infection and to produce a rule for classifying other pediatric patients. Discriminant analysis was applied to predict the probability of a specific categorical outcome based on several explanatory variables (predictors). This study analyzed the differentiation between two hundred pediatric patients attending Landmark University Medical Centre based on their typhoid fever status. The hematological parameters considered were Packed Cell Volume, White Blood Cell count; Neutrophil, Erythrocyte level, Hemoglobin and Platelet count, Assay of samples were performed using standard procedures. Fisher's Linear Discriminant Method was used for classification of variables in this study. With the use of the Fisher's Linear Discrimination method for classification of the obtained data, a minimum value of -0.0067 was obtained implying that any new pediatric patient with a discriminant score above -0.0067 would be diagnosed to be typhoid negative; otherwise, they would be classified as typhoid positive pediatric patients. The efficiency of this method of classification was tested using two approaches; Retribution estimate approach and leaving-one out approach which showed a prevalence rate of typhoid positive patients at 75.8% and 74.7% respectively. This data analysis hypotheses that typhoid fever is highly endemic amongst our study subjects. A point-of-care diagnosis with a strong positive predictive value, which improves pediatric enteric fever diagnosis, is strongly advocated.

Dosage Determination of Ethnopharmacologically Used Fermented Zea mays subsp. mays Liquor Extract of Bambusa vulgaris Schrad. Ex. J.C. Wendel Leaf Against Salmonella typhi

Background: Bambusa vulgaris (bamboo) is a common plant in tropical regions of the world, with multiple biological activities. Cereal steep liquors have been identified to act against some fecal bacteria. Given the increasing prevalence of antimicrobial resistance coupled with the cost of antibiotics, there is a need for mitigation efforts and the shift by locals to herbal products. Methods: The factorial study design was employed. Bamboo leaves were washed, dried, milled, and soxhlet extracted for 16 h using the steep fermented liquor from Zea mays subsp. mays as the solvent. Rotary evaporated extracts of various weights were used to carry out sensitivity and minimum inhibitory concentration (MIC) tests. Oral acute toxicity was determined. The in vivo assay was used to determine the effective dosage for the treatment of infected mice while distilled water and ciprofloxacin served as negative and positive controls, respectively. Results: The average inhibition zone diameters in the sensitivity test at 25, 50, and 100 mg/mL concentrations were 16.20 ± 0.06 mm, 19.10 ± 0.02 mm, and 22.10 ± 0.05 mm, respectively, while the MIC against Salmonella typhi was 25 mg/mL. The extract was found to be safe at up to 5000 mg/kg dose, which means that the LD50 was ≥ 3808 mg/kg. The Widal test revealed that mice responded to treatment with the extract at different concentrations (50, 100, and 200 mg/mL) as the number of days increased. The in vivo assay on day 14 showed the bactericidal property at a dosage of 200 mg/mL. Conclusions: Bamboo leaves extract in steep liquor from fermented yellow maize displayed excellent pharmacological activity against the pathogenic organism of typhoid fever with a potential source of active agents.

Research in a time of enteroids and organoids: how the human gut model has transformed the study of enteric bacterial pathogens

Enteric bacterial pathogens cause significant morbidity and mortality globally. Studies in tissue culture and animal models shaped our initial understanding of these host-pathogen interactions. However, intrinsic shortcomings in these models limit their application, especially in translational applications like drug screening and vaccine development. Human intestinal enteroid and organoid models overcome some limitations of existing models and advance the study of enteric pathogens. In this review, we detail the use of human enteroids and organoids to investigate the pathogenesis of invasive bacteria Shigella, Listeria, and Salmonella, and noninvasive bacteria pathogenic Escherichia coli, Clostridium difficile, and Vibrio cholerae. We highlight how these studies confirm previously identified mechanisms and, importantly, reveal novel ones. We also discuss the challenges for model advancement, including platform engineering to integrate environmental conditions, innate immune cells and the resident microbiome, and the potential for pre-clinical testing of recently developed antimicrobial drugs and vaccines.

Time series analysis of cumulative incidences of typhoid and paratyphoid fevers in China using both Grey and SARIMA models

Typhoid and paratyphoid fevers are common enteric diseases causing disability and death in China. Incidence data of typhoid and paratyphoid between 2004 and 2016 in China were analyzed descriptively to explore the epidemiological features such as age-specific and geographical distribution. Cumulative incidence of both fevers displayed significant decrease nationally, displaying a drop of 73.9% for typhoid and 86.6% for paratyphoid in 2016 compared to 2004. Cumulative incidence fell in all age subgroups and the 0–4 years-old children were the most susceptible ones in recent years. A cluster of three southwestern provinces (Yunnan, Guizhou, and Guangxi) were the top high-incidence regions. Grey model GM (1,1) and seasonal autoregressive integrated moving average (SARIMA) model were employed to extract the long-term trends of the diseases. Annual cumulative incidence for typhoid and paratyphoid were formulated by GM (1,1) as x^(t)=−14.98(e−0.10(t−2004)−e−0.10(t−2005)) and x^(t)=−4.96(e−0.19(t−2004)−e−0.19(t−2005)) respectively. SARIMA (0,1,7) × (1,0,1)₁₂ was selected among a collection of constructed models for high R² and low errors. The predictive models for both fevers forecasted cumulative incidence to continue the slightly downward trend and maintain the cyclical seasonality in near future years. Such data-driven insights are informative and actionable for the prevention and control of typhoid and paratyphoid fevers as serious infectious diseases.

A novel Vi-diphtheria toxoid typhoid conjugate vaccine is safe and can induce immunogenicity in healthy Indonesian children 2-11 years: a phase II preliminary report

BACKGROUND

Typhoid fever caused by Salmonella enteric serovar Typhi (S. Typhi) is a common cause of morbidity in the world. In 2017, 14.3 million cases of Typhoid and paratyphoid fever occurred globally. School age children between 3 to 19 years old are the most affected. Poor sanitation and multi drug resistance have increased the need for vaccines to reduce the global burden of disease. Based on previous trials, typhoid conjugate vaccines have longer- lasting protection, higher efficacy, require fewer doses and are suitable from infancy that allows them to be incorporated into the routine immunization program. Our previous phase I trial proved that a novel Vi-DT typhoid conjugate vaccine is safe and immunogenic in subjects 2-5 and 18-40 years. Our phase II trial consisted of subjects 6 months to 40 years. Our previously published paper on subjects 6 to < 24 months proved that this vaccine is safe and immunogenic for this age group. Therefore, with this paper we aimed to evaluate the safety and immunogenicity in children 2-11 years.

METHODS

A randomized, observer-blind, superiority design of Vi-DT Typhoid conjugate vaccine compared to Vi-polysaccharide vaccine (Vi-PS) phase II study was conducted from October 2018 to December 2018 where 200 subjects aged 2-11 years were recruited. A blood sample prior to vaccination was taken, followed by administration of a single dose of either test vaccine (Vi-DT) or control vaccine (Vi-PS) and then a second blood sample was collected 28 days post vaccination. Adverse reactions were assessed and antibody increment was evaluated at 28 days post vaccination through collected serum sample.

RESULTS

Pain was the most common local reaction. Fever and muscle pain were the most common systemic reactions. Both Vi-DT and Vi-PS groups had roughly the same number of adverse reactions. At 28 days post vaccination, 100% of subjects in the Vi-DT group and 93% of subjects in the Vi-PS group produced antibody increment ≥4 times. The Vi-DT group produced a higher GMT as compared to Vi-PS.

CONCLUSION

Vi-DT vaccine is safe and immunogenic in children 2-11 years old.

TRIAL REGISTRATION

Trial registration number: NCT03460405 .

Immune Modulation and the Development of Fowl Typhoid: A Model of Human Disease?

Salmonella enterica serovar Gallinarum (S. Gallinarum) is the cause of typhoid in chickens but the immune factors that may facilitate the development of typhoid have not been fully elucidated. We show that, in contrast to non-typhoid S. Enteritidis infection, S. Gallinarum significantly reduced nitrite ion production and expression of mRNA for heterophil granulocyte chemoattractants CXCLi2 and IL-6 in chicken monocyte-derived macrophages (chMDMs) (p < 0.05) at 6 h post-infection (pi). S. Gallinarum also reduced IFN-γ and IL-17 expression by CD4⁺ lymphocytes cultured with infected chMDMs for 5 days but did not induce a Th2 phenotype or anergy. In vivo, S. Gallinarum also induced significantly lower expression of CXCLi1, CXCLi2, IL-1β, IL-6 and iNOS mRNA in the caecal tonsil by day 2 pi (p < 0.05–0.01) and consistently lower levels of IFN-γ, IL-18, IL-12, and IL-17. In the spleen, S. Gallinarum induced significantly lower levels of iNOS and IFN-γ (p < 0.01 and 0.05 respectively) and consistently lower levels of IL-18 and IL-12 but significantly greater (p < 0.01) expression of anti-inflammatory IL-10 at day 4 and 5 pi when compared to S. Enteritidis. This immune phenotype was associated with transit from the intestinal tissues to the liver by S. Gallinarum, not observed following S. Enteritidis infection. In conclusion, we report an immune mechanism that may facilitate typhoid disease in S. Gallinarum-infected chickens. However, down-regulation of inflammatory mediators, upregulation of IL-10, and associated liver colonisation are also characteristic of human typhoid, suggesting that this may also be a useful model of typhoid in humans.

Homologous and heterologous re-challenge with Salmonella Typhi and Salmonella Paratyphi A in a randomised controlled human infection model

Enteric fever is a systemic infection caused by Salmonella Typhi or Paratyphi A. In many endemic areas, these serovars co-circulate and can cause multiple infection-episodes in childhood. Prior exposure is thought to confer partial, but incomplete, protection against subsequent attacks of enteric fever. Empirical data to support this hypothesis are limited, and there are few studies describing the occurrence of heterologous-protection between these closely related serovars. We performed a challenge-re-challenge study using a controlled human infection model (CHIM) to investigate the extent of infection-derived immunity to Salmonella Typhi or Paratyphi A infection. We recruited healthy volunteers into two groups: naïve volunteers with no prior exposure to Salmonella Typhi/Paratyphi A and volunteers previously-exposed to Salmonella Typhi or Paratyphi A in earlier CHIM studies. Within each group, participants were randomised 1:1 to oral challenge with either Salmonella Typhi (104 CFU) or Paratyphi A (103 CFU). The primary objective was to compare the attack rate between naïve and previously challenged individuals, defined as the proportion of participants per group meeting the diagnostic criteria of temperature of ≥38°C persisting for ≥12 hours and/or S. Typhi/Paratyphi bacteraemia up to day 14 post challenge. The attack-rate in participants who underwent homologous re-challenge with Salmonella Typhi was reduced compared with challenged naïve controls, although this reduction was not statistically significant (12/27[44%] vs. 12/19[63%]; Relative risk 0.70; 95% CI 0.41-1.21; p = 0.24). Homologous re-challenge with Salmonella Paratyphi A also resulted in a lower attack-rate than was seen in challenged naïve controls (3/12[25%] vs. 10/18[56%]; RR0.45; 95% CI 0.16-1.30; p = 0.14). Evidence of protection was supported by a post hoc analysis in which previous exposure was associated with an approximately 36% and 57% reduced risk of typhoid or paratyphoid disease respectively on re-challenge. Individuals who did not develop enteric fever on primary exposure were significantly more likely to be protected on re-challenge, compared with individuals who developed disease on primary exposure. Heterologous re-challenge with Salmonella Typhi or Salmonella Paratyphi A was not associated with a reduced attack rate following challenge. Within the context of the model, prior exposure was not associated with reduced disease severity, altered microbiological profile or boosting of humoral immune responses. We conclude that prior Salmonella Typhi and Paratyphi A exposure may confer partial but incomplete protection against subsequent infection, but with a comparable clinical and microbiological phenotype. There is no demonstrable cross-protection between these serovars, consistent with the co-circulation of Salmonella Typhi and Paratyphi A. Collectively, these data are consistent with surveillance and modelling studies that indicate multiple infections can occur in high transmission settings, supporting the need for vaccines to reduce the burden of disease in childhood and achieve disease control. Trial registration NCT02192008; clinicaltrials.gov.