Serovar Typhi Infection Research Articles

Antimicrobial Resistance Profile of Salmonella enterica Serovar typhi Isolated from Human Clinical Samples in Ebonyi State, Nigeria

The emergence of resistance to the frequent use of empirical treatment of uncomplicated enteric fever caused by Salmonella enterica serovar Typhi is on the increase. This study was designed to determine the antimicrobial Resistance profile of Salmonella enterica serovar Typhi isolated from human clinical samples in Ebonyi State. A non-duplicated stool culture of Salmonella enterica serovar Typhi of patients diagnosed with typhoid fever at General Hospital Onicha Igboeze were collected from the hospital ward namely: A & E (n = 4), MS (n = 3), FS (n = 3), PD (n = 7), LW (n = 4), ORT (n = 1), LAB (n = 17), THE (n = 9), GOPD (n = 4), MM (n = 3). Antimicrobial studies of Salmonella enterica serovar Typhi were determined using the Kirby–Bauer disk diffusion method. The proportion of resistance ranges from 33 %-100% against colistin, cefepime, nalidixic acid, cefoxitin, amikacin, cefuroxime, and piperacillin-tazobactam but isolates were only susceptible to meropenem 100%. The use of antimicrobial agents for the treatment of Salmonella enterica serovar typhi infection should be guided with antimicrobial susceptibility testing, Nonetheless, the diversity of the Salmonella isolates as a result of the dissemination of these resistant genes is a call for concern and emphasizes a need for an extensive investigation for the presence of these genes in Ebonyi State as well as the implementation of strict antimicrobial policies in a bid to restrict the spread of these resistance genes and prevent the emergence of new resistant strains.

Antimicrobial susceptibility of bacteraemic isolates of Salmonella enterica serovar typhi and paratyphi infection in Pakistan from 2017-2020.

To determine the antibacterial susceptibility pattern of bacteraemia isolates of Salmonella enterica serovar typhi and paratyphi. The retrospective descriptive observational study was conducted at the Microbiology section of Dow Diagnostic Research and Reference Laboratory, and comprised blood culture reports from January 1, 2017, to Dec 30, 2020, which were screened for the presence of Salmonella typhi and paratyphi growth The frequency of the isolates and their antibiotic resistance patterns were analysed. Data was analysed using SPSS 20. Of the 174,190 blood culture samples, 62,709(36%) were positive for bacterial growth. Salmonella were isolated in 8,689(13.8%) samples of which 8,041(92.5%) were Salmonella typhi, 529(6%) were Salmonella paratyphi A and 119(1.3%) were Salmonella paratyphi B. There was a drastic increase in resistance to third-generation cephalosporin in Salmonella typhi from 71(12.8%) in 2017 to 1,420(71%) in 2018, 2,850(74.6%) in 2019 and 1,251(77%) in 2020. All isolates were sensitive to meropenem and azithromycin. A high number of extensively drug-resistant typhoid cases due to Salmonella typhi were found. All isolates were sensitive to meropenem and azithromycin.

Identification of collaborative cross mouse strains permissive to Salmonella enterica serovar Typhi infection

Salmonella enterica serovar Typhi is the causative agent of typhoid fever restricted to humans and does not replicate in commonly used inbred mice. Genetic variation in humans is far greater and more complex than that in a single inbred strain of mice. The Collaborative Cross (CC) is a large panel of recombinant inbred strains which has a wider range of genetic diversity than laboratory inbred mouse strains. We found that the CC003/Unc and CC053/Unc strains are permissive to intraperitoneal but not oral route of S. Typhi infection and show histopathological changes characteristic of human typhoid. These CC strains are immunocompetent, and immunization induces antigen-specific responses that can kill S. Typhi in vitro and control S. Typhi in vivo. Our results indicate that CC003/Unc and CC053/Unc strains can help identify the genetic basis for typhoid susceptibility, S. Typhi virulence mechanism(s) in vivo, and serve as a preclinical mammalian model system to identify effective vaccines and therapeutics strategies.

Salmonella enterica serovar Typhi infection: a public health problem in Latin America and the automated microbiological methods

Salmonella enterica serovar Typhi infection: a public health problem in Latin America and the automated microbiological methods

B Cells Control Mucosal-Associated Invariant T Cell Responses to Salmonella enterica Serovar Typhi Infection Through the CD85j HLA-G Receptor.

Mucosal-associated invariant T (MAIT) cells are an innate-like population of T cells that display a TCR Vα7.2+ CD161+ phenotype and are restricted by the nonclassical MHC-related molecule 1 (MR1). Although B cells control MAIT cell development and function, little is known about the mechanisms underlying their interaction(s). Here, we report, for the first time, that during Salmonella enterica serovar Typhi (S. Typhi) infection, HLA-G expression on B cells downregulates IFN-γ production by MAIT cells. In contrast, blocking HLA-G expression on S. Typhi-infected B cells increases IFN-γ production by MAIT cells. After interacting with MAIT cells, kinetic studies show that B cells upregulate HLA-G expression and downregulate the inhibitory HLA-G receptor CD85j on MAIT cells resulting in their loss. These results provide a new role for HLA-G as a negative feedback loop by which B cells control MAIT cell responses to antigens.

Prevalence of Salmonella enterica serovar Typhi infection, its associated factors and antimicrobial susceptibility patterns among febrile patients at Adare general hospital, Hawassa, southern Ethiopia

BackgroundSalmonellas enterica serovar Typhi (S.typhi) causes typhoid fever and is a global health problem, especially in developing countries like Ethiopia. But there is a little information about prevalence and factors association with S.typhi and its antimicrobial susceptibility pattern in Ethiopia especially in the study area.The aim of this study was to determine the prevalence of S.typhi infection, its associated factors and antimicrobial susceptibility pattern among patient with a febrile illness at Adare General Hospital, Hawassa, Southern Ethiopia.MethodsHospital based cross sectional study was conducted among 422 febrile patients from May 23, 2018 to October 20, 2018. A 5 ml venous blood was collected from each febrile patient. Culture and biochemical test were performed for each isolate. Antimicrobial susceptibility testing was performed for each isolate using modified Kirby-Bauer disk diffusion techniques.ResultIn this study, the prevalence of S.typhi among febrile illness patients at Adare General Hospital was 1.6% [95% confidence interval (CI): 0.5–2.9]. The age of the study subjects were ranged from 15 to 65 years (mean age 32 years). It was observed that participants who came from rural area had 8 times (AOR 8.27: 95% CI: 1.33, 51.55) more likely to had S. typhi infection when compared with urban dwellers. The microbial susceptibility testing revealed that all six of S.typhi isolates showed sensitive to Ceftriaxone and all 6 isolates showed resistant to nalidixic acid and Cefotaxime and 5(83.3%) susceptible to Chloramphenicol and Ciprofloxaciline. Multidrug resistance (resistance to three or more antibiotics) was observed among most of the isolates.ConclusionS. typhi bacteraemia is an uncommon but important cause of febrile illness in our study population. Ceftriaxone therapy is a suitable empirical antibiotic for those that are unwell and suspected of having this illness. Further surveillance is required to monitor possible hanging antibiotic resistant patterns in Ethiopia.

Core Fucosylation of Intestinal Epithelial Cells Protects Against Salmonella Typhi Infection via Up-Regulating the Biological Antagonism of Intestinal Microbiota.

The fucosylated carbohydrate moieties on intestinal epithelial cells (IECs) are involved in the creation of an environmental niche for commensal and pathogenic bacteria. Core fucosylation catalyzed by fucosyltransferase 8 (Fut8) is the major fucosylation pattern on the N-glycans of the surface glycoproteins on IECs, however, the role of IECs core fucosylation during infection remains unclear. This study was conducted to investigate the interaction between IECs core fucosylation and gut microbiota, and the effects of this interaction on protecting Salmonella enterica subsp. enterica serovar Typhi (S. Typhi) infection. Firstly, the Fut8+/+ and Fut8+/– mice were infected with S. Typhi. The level of IECs core fucosylation and protein expression of intestinal mucosa were then detected by LCA blot and Western blot, respectively. The gut microbiota of Fut8+/+ and Fut8+/– mice before and after S. Typhi infection was assessed by 16S rRNA sequencing. Our results showed that core fucosylation was ubiquitous expressed on the intestinal mucosa of mice and had significant effects on their gut microbiota. Fut8+/– mice was more susceptive to S. Typhi infection than Fut8+/+ mice. Interestingly, infection of S. Typhi upregulated the core fucosylation level of IECs and increased the abundances of beneficial microorganisms such as Lactobacillus and Akkermansia spp. Further in vitro and in vivo studies demonstrated that Wnt/β-catenin signaling pathway mediated the elevation of IECs core fucosylation level upon infection of S. Typhi. Taken together, our data in this study revealed that the IECs core fucosylation plays an important role in protecting against S. Typhi infection via up-regulating the biological antagonism of intestinal microbiota.

Quantitative Assessment of an Artificial Neural Network for the Variation in Immunity to Salmonella Infection Among Sudanese and Chinese Populations and the Relationship Between HLA-DQB1 and Antibody: A Preliminary Study

Background: Salmonella enterica serovar typhi infection is a worldwide bacterial disease still remains a public health problem and the resistance to the infection and clearance of the bacteria may differ between Sudanese and Chinese populations. Objectives: We aimed to evaluate the difference in immunity to Salmonella infection and the relationship of HLA-DQB1 and antibody in the two populations using an artificial neural network (ANN). Methods: An ANN was constructed by data collected from resolved Salmonella-infected patients. The variation in immunity to Salmonella in the two groups was compared using the Mann-Whitney U test. The relationship between human leukocyte antigen (HLA) gene and the antibody was assessed by Spearman correlation. Binary Logistic regression assessed whether variables were independent in the two groups. The quantitative variations in immunity to S. typhi in the two groups were assessed by ANN using SPSS software version 21.0. Results: A high variation in immunity to S. typhi between Sudanese and Chinese in affinity (P 0.05). There was a high variation in HLA-DQB1*03 (P 0.05). A clear correlation was observed between HLA-DQB1*05 and the antibody (P < 0.05). The standardized percentage of the effect of HLA-DQB1 gene on the variation of immunity in the two groups for HLA-DQB1*06 (100%) was much higher than the other HLA-DQB1 alleles. Conclusions: A high variation in the HLA-DQB1 gene between Sudanese and Chinese populations may be associated with the difference in immunity against S. typhi infection.

Typhoid in Laos: An 18-Year Perspective.

.Although typhoid is endemic to Southeast Asia, very little is known about the disease in Laos. Typhoid vaccination is not included in the national immunization program. Although sanitation has improved, one million people still do not have access to basic clean water sources. We describe the epidemiology and antimicrobial susceptibility patterns of Salmonella enterica serovar Typhi (S. Typhi) infection in Laos based on isolates accrued over 18 years at Mahosot Hospital, Vientiane. All blood cultures collected from patients presenting with fever submitted to the Microbiology Laboratory at Mahosot Hospital (February 2000–December 2018) were included. This included patients from Vientiane and four provincial hospitals and one typhoid outbreak investigation. A total of 913 (1.5%) of 60,384 blood cultures were positive for S. Typhi. The majority of isolates with data available (712/898, 79.3%) were susceptible to all antibiotics tested, with 59 (6.5%) multidrug-resistant (MDR) isolates, mostly from one outbreak. Of 854 isolates, 12 (1.4%) were fluoroquinolone resistant. Patient admissions peaked between March and June at the end of the dry season. Although there are key limitations, these data give the first detailed epidemiological evidence of typhoid in Laos. However, estimates will be greatly influenced by access to blood culture services and health-seeking behavior. Although typhoid multidrug resistance and fluoroquinolone resistance are not currently major issues in Laos, continued surveillance and improved antibiotic stewardship are necessary to forestall worsening of the situation. Cost-effectiveness analysis is needed to inform decisions regarding typhoid vaccine introduction.

Analysis of Caenorhabditis elegans phosphoproteome reveals the involvement of a molecular chaperone, HSP-90 protein during Salmonella enterica Serovar Typhi infection

Being a primary and prerequisite Post Translational Modification (PTM), protein phosphorylation mediates the defense mechanisms that presides host defense against a pathogen attack. Hence, the current study was intended to uncover the role of regulatory proteins and their PTMs with special attention to phosphorylation during pathogen attack, using C. elegans as a host and S. Typhi as an interacting pathogen. The study was initiated with the identification of differential regulation of the crucial immune regulatory kinases such as PMK-1, JNK-1 and SGK-1 through immunoblotting analysis, which revealed up-regulation of kinases during 48 h of S. Typhi infection. Subsequent the phosphoproteome profiling of S. Typhi infected C. elegans, using TiO2 Column Chromatography followed by MALDI-ToF-ToF-MS, uncovered the regulated phosphoprotein players resulting in the identification of 166 and 54 proteins from gel-free and gel-based analysis, respectively. HSP-90 was found to be a central player from the interactome analyses and its role during pathogenic defense was validated using immunoblotting. Furthermore, the protein disorders of the identified phosphoproteins have been extensively analysed in silico. This study suggests that S. Typhi interferes with the homeostasis of chaperone molecules by kinetically interfering with the phosphorylation of the downstream pathway players of MAPK and JNK.

Role of Environmental Factors in Shaping Spatial Distribution of Salmonella enterica Serovar Typhi, Fiji.

Fiji recently experienced a sharp increase in reported typhoid fever cases. To investigate geographic distribution and environmental risk factors associated with Salmonella enterica serovar Typhi infection, we conducted a cross-sectional cluster survey with associated serologic testing for Vi capsular antigen–specific antibodies (a marker for exposure to Salmonella Typhi in Fiji in 2013. Hotspots with high seroprevalence of Vi-specific antibodies were identified in northeastern mainland Fiji. Risk for Vi seropositivity increased with increased annual rainfall (odds ratio [OR] 1.26/quintile increase, 95% CI 1.12–1.42), and decreased with increased distance from major rivers and creeks (OR 0.89/km increase, 95% CI 0.80–0.99) and distance to modeled flood-risk areas (OR 0.80/quintile increase, 95% CI 0.69–0.92) after being adjusted for age, typhoid fever vaccination, and home toilet type. Risk for exposure to Salmonella Typhi and its spatial distribution in Fiji are driven by environmental factors. Our findings can directly affect typhoid fever control efforts in Fiji.

Human genetic variation in VAC14 regulates Salmonella invasion and typhoid fever through modulation of cholesterol

Risk, severity, and outcome of infection depend on the interplay of pathogen virulence and host susceptibility. Systematic identification of genetic susceptibility to infection is being undertaken through genome-wide association studies, but how to expeditiously move from genetic differences to functional mechanisms is unclear. Here, we use genetic association of molecular, cellular, and human disease traits and experimental validation to demonstrate that genetic variation affects expression of VAC14, a phosphoinositide-regulating protein, to influence susceptibility to Salmonella enterica serovar Typhi (S Typhi) infection. Decreased VAC14 expression increased plasma membrane cholesterol, facilitating Salmonella docking and invasion. This increased susceptibility at the cellular level manifests as increased susceptibility to typhoid fever in a Vietnamese population. Furthermore, treating zebrafish with a cholesterol-lowering agent, ezetimibe, reduced susceptibility to S Typhi. Thus, coupling multiple genetic association studies with mechanistic dissection revealed how VAC14 regulates Salmonella invasion and typhoid fever susceptibility and may open doors to new prophylactic/therapeutic approaches.

Salmonella Typhi: A cause of septic arthritis knee: A Rare entity.

Salmonella species enterica subspecies enterica serovar Typhi infection may result in various presentations like enteric fever, septicaemia with and without local suppurative lesions, gastroenteritis and the carrier state. Arthritis is an uncommon and rare manifestation of salmonella infection. Here, we report a case of septic arthritis of knee in a patient with benign prostate hypertrophy and catheter in situ . The case is presented for its rarity and to highlight the atypical manifestations of Salmonella Typhi in endemic regions. Hence salmonella species must always be kept in mind for the differential diagnosis of septic arthritis in a clinically relevant setting. Although few case reports have been reported signifying Salmonella enteritidis as a cause of septic arthritis knee however this is the first report of septic arthritis knee caused by Salmonella Typhi .

Diagnosing Salmonella enterica Serovar Typhi Infections by Polymerase Chain Reaction Using EDTA Blood Samples of Febrile Patients From Burkina Faso.

Globally, there are an estimated 22 million cases of Salmonella enterica serovar Typhi infection each year. However, this figure is likely to be an underestimate due to the low sensitivity of blood culture in S. Typhi diagnosis. The aim of this study was to diagnose S. Typhi by conventional polymerase chain reaction (PCR) using patient's blood preserved with ethylenediamine tetraacetic acid (EDTA). From April 2012 to September 2013, typhoid fever surveillance was conducted in Polesgo and Nioko, 2 dry slum areas in Ouagadougou, Burkina Faso. Blood culture was performed for febrile patients using an automated blood culture system. Additional blood was collected in EDTA tubes from those patients and preserved at -80°C. DNA was extracted from EDTA blood and PCR was performed to identify presence of S. Typhi. Randomly selected PCR products were further sequenced to identify S. Typhi-specific amplicons. Of 1674 patients, S. Typhi was isolated from 18 (1.1%) individuals by blood culture. EDTA blood was collected from 1578 patients, of which 298 EDTA samples were tested by PCR. Salmonella Typhi-specific DNA was identified in 44 (14.8%) samples. The sensitivity of S. Typhi-specific PCR from EDTA blood was 89% (74%-100%) among the blood culture-positive cases. Sixteen S. Typhi-positive PCR products were sequenced, and 13 retrieved the sequence of a S. Typhi-specific amplicon. These findings suggest that blood culture-based diagnoses of S. Typhi underestimate the burden of typhoid fever in Burkina Faso. PCR could be considered as an alternative method for the identification and diagnosis of S. Typhi in blood samples.

Salmonella Manipulation of Host Signaling Pathways Provokes Cellular Transformation Associated with Gallbladder Carcinoma.

Cancer is fueled by deregulation of signaling pathways in control of cellular growth and proliferation. These pathways are also targeted by infectious pathogens en route to establishing infection. Gallbladder carcinoma (GBC) is frequent in the Indian subcontinent, with chronic Salmonella enterica serovar Typhi infection reported as a significant risk factor. However, direct association and causal mechanisms between Salmonella Typhi infection and GBC have not been established. Deconstructing the epidemiological association between GBC and Salmonella Typhi infection, we show that Salmonella enterica induces malignant transformation in predisposed mice, murine gallbladder organoids, and fibroblasts, with TP53 mutations and c-MYC amplification. Mechanistically, activation of MAPK and AKT pathways, mediated by Salmonella enterica effectors secreted during infection, is critical to both ignite and sustain transformation, consistent with observations in GBC patients from India. Collectively, our findings indicate that Salmonella enterica can promote transformation of genetically predisposed cells and is a causative agent of GBC.

Evaluation of TUBEX-TF and OnSite Typhoid IgG/IgM Combo rapid tests to detect Salmonella enterica serovar Typhi infection during a typhoid outbreak in Harare, Zimbabwe.

BackgroundSalmonella enterica serovar Typhi, the causative agent of typhoid, is endemic in most parts of the world especially in Africa. Reliable and rapid diagnosis of the bacterium is therefore critical for confirmation of all suspected typhoid cases. In many parts of Zimbabwe, laboratory capacity to isolate the microorganism by culture method as a way of diagnosis has limitations. In this study, two rapid serological kits, TUBEX-TF and OnSite Typhoid IgG/IgM Combo, were evaluated for possible expeditious diagnosis of Salmonella enterica serovar Typhi infection during a typhoid outbreak in Zimbabwe.MethodsBlood was collected from patients with clinical signs and symptoms of typhoid in Harare, Zimbabwe during an outbreak. The standard culture method was used to diagnose the disease. Two rapid kits, the TUBEX-TF and OnSite Typhoid IgG/IgM Combo, were also used in parallel to diagnose typhoid according to manufacturers’ instructions. The diagnostic accuracy of the two kits was evaluated using the culture method as the gold standard.ResultsFrom all the cases diagnosed by the blood culture (n = 136), we enrolled 131 patients for the TUBEX-TF and 136 for the OnSite Typhoid IgG/IgM Combo tests. With the culture method as a reference standard, we found that TUBEX-TF test was 100% sensitive and 94.12% specific, with 63.16% positive and 100% negative predictive values (NPVs) and the OnSite Typhoid IgG/IgM Combo test was 100% sensitive and 94.35% specific, with 63.16% positive and 100% NPVs.ConclusionOur results indicated that TUBEX-TF and OnSite Typhoid IgG/IgM Combo rapid tests were useful tools for the rapid diagnosis of Salmonella enterica serovar Typhi infection during typhoid outbreaks in Zimbabwe. The tests performed very well in laboratory evaluations of blood culture-confirmed typhoid cases in Harare, Zimbabwe.

Prevalence of Salmonellosis among Food Handlers and the Health Implications on the Food Consumers in Lagos State, Nigeria

Food borne diseases/illnesses (food borne infections) are global public health problem both in developed and developing countries such as Nigeria. Food handlers play an important role in the transmission of food-borne diseases. This research work is aimed to determine the prevalence of salmonellosis among food handlers and its implications on the health of food consumers in Lagos, Southwest Nigeria. Two hundred and thirty five (235) blood samples were collected into EDTA bottles from the food handlers at various locations in Victoria Island (Lagos Island) and Bariga (Lagos mainland) which were analyzed using standard methods. Questionnaires were distributed and collated among 235 respondents (food handlers) to test their knowledge on food safety. The results showed that 74 (31.5%) of the studied population had either previous or recent Salmonella infection as indicated by IgG and IgM anti-Salmonella immunoglobulin while 161 (68.5%) had neither recent nor previous infection. Ninety three (93) respondents were males while One hundred and forty two (142) were females of active working age bracket of 11- 60 years old. Among 93 males screened, 26(28.0%) were infected, 67(72.0%) were not infected while 48(33.8%) females were infected out of 142 females screened for Salmonella enterica serovar Typhi and Paratyphi infections. Regression and T-test statistical analysis reviewed that since F cal>F tab (1.776>0.969) and t cal>t tab (6.5>5.0), it can be concluded that food handlers were not responsible for food borne infections but potential risk factors in Lagos, Southwest, Nigeria.

Development and evaluation of a multiple-locus variable-number tandem-repeats analysis assay for subtyping Salmonella typhi strains from Sub-Saharan Africa

Background: Typhoid fever a major public health problem in developing countries. Epidemiological investigations of Salmonella enterica serovar Typhi (Salmonella Typhi) infections using molecular sub-typing methods are challenging due to the highly homologous nature of Salmonella Typhi strains. In recent years, several approaches in using multiple-locus variable-number tandem-repeats analysis (MLVA) for molecular sub-typing of Salmonella Typhi have been made. To date, a standardized set of variable-number tandem-repeats (VNTR) loci for the typing of homologous Salmonella Typhi strains has not been established. The aim of our study was to develop and evaluate a MLVA assay consisting of 5 VNTR markers to analyse Salmonella Typhi strains from Sub-Saharan Africa (SSA). Methods & Materials: To develop and evaluate the MLVA assay, 50 Salmonella Typhi strains from humans were selected from the culture collection at the Centre for Enteric Diseases (CED) at the National Institute for Communicable Diseases (NICD) from a potential 1080 isolates. This strain panel represented the diverse Salmonella Typhi pulsed-field gel electrophoresis (PFGE) profiles in the CED database, specimen collection dates and geographic areas within the SSA region. The 50 Salmonella Typhi strains were used to evaluate 12 polymorphic VNTR loci that were previously published. These include TR1, TR2, TR3, TR4, TR5, Sal02, Sal06, Sal10, Sal16, Sal20, TR4500 and TR4600. The assay included PCR amplification of VNTR loci using fluorescently labelled primers and size determination of PCR products by capillary electrophoresis. Results: Of the 12 VNTR loci that were evaluated, 5 (TR3, TR4, TR5, Sal06, Sal10 and TR4500) were found unsuitable as they showed poor allele variation (between 1 and 3 alleles). The remaining 6 VNTR loci showed good allele variation and good diversity indices; with Sal20, Sal 16 and TR1 having 6, 9 and 11 alleles respectively; and Sal02, TR4699 and TR2 having 15, 20 and 23 alleles respectively. Conclusion: In summary, we have identified 6 polymorphic VNTR loci suitable for MLVA analysis of Salmonella Typhi strains. The five most diverse VNTR loci will be selected for the MLVA assay and will be used to analyse Salmonella Typhi strains from SSA. This work will assist in rapidly identifying strain relatedness and assist outbreak detection in typhoid fever outbreaks.

Use of multilocus variable-number tandem repeat analysis in molecular subtyping of Salmonella enterica serovar Typhi isolates

We evaluated 11 variable number tandem repeat (VNTR) markers for the epidemiological investigation of Salmonella enterica serovar Typhi (S. Typhi) infection and compared the results to those obtained by PFGE. PFGE, using one or two restriction enzymes (XbaI and BlnI), was insufficient to differentiate between some isolates that were epidemiologically unlinked. Multilocus variable-number tandem repeat analysis (MLVA)-8, based on analysis of the eight most variable VNTRs, displayed a high level of discrimination when distinguishing between epidemiologically unlinked isolates that could not be discerned by PFGE with two enzymes. An MLVA-8 typing scheme could be implemented as a routine subtyping tool for the epidemiological investigation of S. Typhi infections. Because seven of the 11 VNTRs are highly variable, the VNTR markers may only be useful in determining genetic relationships among very closely related isolates in short-term epidemiological studies and not for discerning S. Typhi clones.

Evaluation of a newly developed ELISA against Widal, TUBEX-TF and Typhidot for typhoid fever surveillance

Typhoid fever is endemic in many parts of the world and represents a major cause of acute febrile illness (AFI). Rapid and accurate laboratory methods for diagnosis of this disease are needed for both patient care and surveillance situations. Serum samples were collected from AFI patients and used to evaluate the performance of a newly developed ELISA assay that uses a mixture of somatic and flagellar antigens to detect the total antibody response against Salmonella enterica subspecies enterica serovar Typhi (S. Typhi) infection. The levels of Ig isotype response (IgG, IgM and IgA) were also evaluated, and results were compared to those of TUBEX-TF and Typhidot commercial kits. Of 234 culture-confirmed typhoid patients, the total Ig ELISA diagnosed 93% compared to 71% using Widal test. This sensitivity level (93%) is higher than that observed for the individual Ig ELISAs (IgG 75%; IgM 79%; IgA 57%) and the commercial tests TUBEX-TF (75%), Typhidot IgM (63%) and Typhidot IgG (28%). An agreement of 78% was achieved between the total Ig ELISA and Widal test. The average specificity of the ELISA was 96%. Using ELISA, up to 200 samples can be tested per run with cost per test at US$0.20. The developed ELISA shows superior sensitivity and specificity, when compared to Widal, TUBEX-TF and Typhidot assays, is more cost effective and allows higher throughput. This method is highly recommended for active surveillance studies or outbreak investigations of typhoid fever.