Typhoid fever

Clinical and microbiological characterization of Salmonella spp. isolates from patients treated in a university hospital in South America between 2012-2021: a cohort study

BACKGROUND

Salmonellosis is a major cause of morbidity and mortality and one of the most frequent etiologies of diarrhea in the world. Mortality due to Salmonellosis in Latin America still poorly understood, and there is a lack of studies that evaluate resistance and clinical manifestations. The aims of this study were to characterize patients infected with Salmonella spp. seen in a university hospital in Colombia between 2012 and 2021, to evaluate trends in antibiotic resistance and to determine the proportion of overall mortality and related factors.

METHODS

Retrospective observational study. All patients with microbiological diagnosis of Salmonella spp. were included. The sociodemographic, clinical and microbiological characteristics were described, and the proportion of antibiotic resistant isolates per year was estimated. The prevalence of mortality according to age groups was calculated. Log binomial regression models were used to establish factors associated with mortality.

RESULTS

Five hundred twenty-two patients were analyzed. Salmonellosis accounted for 0.01% of all medical consultations. The median age was 16 years old. The most common clinical presentation was gastroenteric syndrome (77.1%) and symptoms included diarrhea (79.1%), fever (66.7%), abdominal pain (39.6%) and vomiting (35.2%). Of the Salmonella spp. isolates, 78.2% were not classified, 19.1% corresponded to non-typhoidal Salmonella and 2.7% to Salmonella typhi. Mortality occurs in 4.02% of the patients and was higher in patients with hematologic malignancy (11.6%). When analyzing by age group, the proportion of deaths was 2.8% in patients aged 15 years or younger, while in those older than 15 years it was 5.4%. Factors associated to mortality where bacteremia (aPR = 3.41 CI95%: 1.08-10.76) and to require treatment in the ICU (aPR = 8.13 CI95%: 1.82-37.76). In the last 10 years there has been a steady increase in resistance rates to ciprofloxacin, ampicillin, ampicillin/sulbactam and ceftriaxone, reaching rates above 60% in recent years.

CONCLUSIONS

Despite improved availability of antibiotics for the treatment of salmonellosis in the past decades, mortality due to salmonellosis continues occurring in children and adults, mainly in patients with hematological malignancies and bacteremia. Antibiotic resistance rates have increased significantly over the last 10 years. Public health strategies for the control of this disease should be strengthened, especially in vulnerable populations.

Persistent Salmonella enterica serovar Typhi sub-populations within host interrogated by whole genome sequencing and metagenomics

Salmonella enterica serovar Typhi (S. Typhi) causes typhoid fever and, in some cases, chronic carriage after resolution of acute disease. This study examined sequential isolates of S. Typhi from a single host with persistent asymptomatic infection. These isolates, along with another S. Typhi isolate recovered from a household contact with typhoid fever, were subjected to whole genome sequencing and analysis. In addition, direct sequencing of the bile fluid from the host with persistent infection was also performed. Comparative analysis of isolates revealed three sub-populations of S. Typhi with distinct genetic patterns. Metagenomic sequencing recognised only two of the three sub-populations within the bile fluid. The detection and investigation of insertion sequences IS10R and associated deletions complemented analysis of single nucleotide polymorphisms. These findings improve our understanding of within-host dynamics of S. Typhi in cases of persistent infection and inform epidemiological investigations of transmission events associated with chronic carriers.

From Eberthella typhi to Salmonella Typhi: The Fascinating Journey of the Virulence and Pathogenicity of Salmonella Typhi

Salmonella Typhi (S. Typhi), the invasive typhoidal serovar of Salmonella enterica that causes typhoid fever in humans, is a severe threat to global health. It is one of the major causes of high morbidity and mortality in developing countries. According to recent WHO estimates, approximately 11-21 million typhoid fever illnesses occur annually worldwide, accounting for 0.12-0.16 million deaths. Salmonella infection can spread to healthy individuals by the consumption of contaminated food and water. Typhoid fever in humans sometimes is accompanied by several other critical extraintestinal complications related to the central nervous system, cardiovascular system, pulmonary system, and hepatobiliary system. Salmonella Pathogenicity Island-1 and Salmonella Pathogenicity Island-2 are the two genomic segments containing genes encoding virulent factors that regulate its invasion and systemic pathogenesis. This Review aims to shed light on a comparative analysis of the virulence and pathogenesis of the typhoidal and nontyphoidal serovars of S. enterica.

Hacking the Immune Response to Solid Tumors: Harnessing the Anti-Cancer Capacities of Oncolytic Bacteria

Oncolytic bacteria are a classification of bacteria with a natural ability to specifically target solid tumors and, in the process, stimulate a potent immune response. Currently, these include species of Klebsiella, Listeria, Mycobacteria, Streptococcus/Serratia (Coley's Toxin), Proteus, Salmonella, and Clostridium. Advancements in techniques and methodology, including genetic engineering, create opportunities to "hijack" typical host-pathogen interactions and subsequently harness oncolytic capacities. Engineering, sometimes termed "domestication", of oncolytic bacterial species is especially beneficial when solid tumors are inaccessible or metastasize early in development. This review examines reported oncolytic bacteria-host immune interactions and details the known mechanisms of these interactions to the protein level. A synopsis of the presented membrane surface molecules that elicit particularly promising oncolytic capacities is paired with the stimulated localized and systemic immunogenic effects. In addition, oncolytic bacterial progression toward clinical translation through engineering efforts are discussed, with thorough attention given to strains that have accomplished Phase III clinical trial initiation. In addition to therapeutic mitigation after the tumor has formed, some bacterial species, referred to as "prophylactic", may even be able to prevent or "derail" tumor formation through anti-inflammatory capabilities. These promising species and their particularly favorable characteristics are summarized as well. A complete understanding of the bacteria-host interaction will likely be necessary to assess anti-cancer capacities and unlock the full cancer therapeutic potential of oncolytic bacteria.

Severe Typhoid Fever Complicated by Superior Mesenteric and Splenic Vein Thrombosis

Typhoid fever (Typhoid or enteric fever) is still the most common bacterial bloodstream infection worldwide, caused by Salmonella typhi. The transmission route is indirect through passive vehicles such as contaminated water or food. Main clinical findings are a fever lasting more than three days, abdominal symptoms, leukocytosis, and anemia. Typhoid can cause a wide range of multi-organ complications. We report a particularly severe form of this infection complicated by superior mesenteric vein and splenic vein thrombosis, an extremely uncommon manifestation.

Determinants of persistent Salmonella infections

Persistent bacterial infections constitute an enormous challenge for public health. Amongst infections with other bacteria, infections with typhoidal and nontyphoidal Salmonella enterica serovars can result in long-term infections of the human and animal host. Persistent infections that are asymptomatic are difficult to identify and thus can serve as a silent reservoir for transmission. Symptomatic persistent infections are often difficult to treat as they harbor a combination of antibiotic-tolerant and antibiotic-resistant bacteria and boost the spread of genetic antibiotic resistance. In the last couple of years, the field has made some major progress in understanding the role of persisters, their reservoirs as well as their interplay with host factors in persistent Salmonella infections.

Salmonella Enteritidis activates inflammatory storm via SPI-1 and SPI-2 to promote intracellular proliferation and bacterial virulence

Salmonella Enteritidis is an important intracellular pathogen, which can cause gastroenteritis in humans and animals and threaten life and health. S. Enteritidis proliferates in host macrophages to establish systemic infection. In this study, we evaluated the effects of Salmonella pathogenicity island-1 (SPI-1) and SPI-2 to S. Enteritidis virulence in vitro and in vivo, as well as the host inflammatory pathways affected by SPI-1 and SPI-2. Our results show that S. Enteritidis SPI-1 and SPI-2 contributed to bacterial invasion and proliferation in RAW264.7 macrophages, and induced cytotoxicity and cellular apoptosis of these cells. S. Enteritidis infection induced multiple inflammatory responses, including mitogen-activated protein kinase (ERK-mediated) and Janus kinase-signal transducer and activator of transcript (STAT) (STAT2-mediated) pathways. Both SPI-1 and SPI-2 were necessary to induce robust inflammatory responses and ERK/STAT2 phosphorylation in macrophages. In a mouse infection model, both SPIs, especially SPI-2, resulted in significant production of inflammatory cytokines and various interferon-stimulated genes in the liver and spleen. Activation of the ERK- and STAT2-mediated cytokine storm was largely affected by SPI-2. S. Enteritidis ΔSPI-1-infected mice displayed moderate histopathological damage and drastically reduced bacterial loads in tissues, whereas only slight damage and no bacteria were observed in ΔSPI-2- and ΔSPI-1/SPI-2-infected mice. A survival assay showed that ΔSPI-1 mutant mice maintained a medium level of virulence, while SPI-2 plays a decisive role in bacterial virulence. Collectively, our findings indicate that both SPIs, especially SPI-2, profoundly contributed to S. Enteritidis intracellular localization and virulence by activating multiple inflammatory pathways.

Salmonella Durban meningitis: case report and genomics study

BACKGROUND

Bacterial meningitis caused by non-typhoid Salmonella can be a fatal condition which is more common in low and middle-income countries.

CASE PRESENTATION

We report the case of a Salmonella meningitis in a Belgian six-month old male infant. The first clinical examination was reassuring, but after a few hours, his general state deteriorated. A blood test and a lumbar puncture were therefore performed. The cerebrospinal fluid analysis was compatible with a bacterial meningitis which was later identified by the NRC (National Reference Center) as Salmonella enterica serovar Durban.

CONCLUSIONS

In this paper, we present the clinical presentation, genomic typing, and probable sources of infection for an unusually rare serovar of Salmonella. Through an extended genomic analysis, we established its relationship to historical cases with links to Guinea.

Typhoid Control in an Era of Antimicrobial Resistance: Challenges and Opportunities

Historically, typhoid control has been achieved with water and sanitation interventions. Today, in an era of rising antimicrobial resistance (AMR), two World Health Organization-prequalified vaccines are available to accelerate control in the shorter term. Meanwhile, water and sanitation interventions could be implemented in the longer term to sustainably prevent typhoid in low- and middle-income countries. This article first approaches typhoid control from a historical perspective, subsequently presents how vaccination could complement water and sanitation activities, and finally discusses the challenges and opportunities for impactful control of typhoid infection. It also addresses data blind spots and knowledge gaps to focus on for typhoid control and to ultimately progress towards elimination. This article presents a synthesis of discussions held in December 2021 during a roundtable session at the "12th International Conference on Typhoid and Other Invasive Salmonelloses".

The Prevalence of Undiagnosed Salmonella enterica Serovar Typhi in Healthy School-Aged Children in Osun State, Nigeria

Typhoid fever remains a significant public health concern due to cases of mis-/overdiagnosis. Asymptomatic carriers play a role in the transmission and persistence of typhoid fever, especially among children, where limited data exist in Nigeria and other endemic countries. We aim to elucidate the burden of typhoid fever among healthy school-aged children using the best surveillance tool(s). In a semi-urban/urban state (Osun), 120 healthy school-aged children under 15 years were enrolled. Whole blood and fecal samples were obtained from consenting children. ELISA targeting the antigen lipopolysaccharide (LPS) and anti-LPS antibodies of Salmonella Typhi, culture, polymerase chain reaction (PCR), and next-generation sequencing (NGS) were used to analyze the samples. At least one of the immunological markers was detected in 65.8% of children, with 40.8%, 37.5%, and 39% of children testing positive for IgM, IgG, and antigen, respectively. Culture, PCR, and NGS assays did not detect the presence of Salmonella Typhi in the isolates. This study demonstrates a high seroprevalence of Salmonella Typhi in these healthy children but no carriage, indicating the inability to sustain transmission. We also demonstrate that using a single technique is insufficient for typhoid fever surveillance in healthy children living in endemic areas.

Propionate reduces the viability of Salmonella enterica Serovar Typhi in macrophages by propionylation of PhoP K102

Propionate, a major constituent of short chain fatty acids, has recently been reported to be involved in both prokaryotic and eukaryotic lysine propionylation (Kpr). However, the propionylation characteristics of the enteric pathogen Salmonella enterica serovar Typhi (S. Typhi) following invasion of the human gut under the influence of propionate, whether virulence is affected, and the underlying mechanisms are not yet known. In the present study, we report that propionate significantly reduces the viability of S. Typhi in macrophages through intra-macrophage survival assays. We also demonstrate that the concentration of propionate and the propionate metabolic intermediate propionyl coenzyme A can affect the level of modification of PhoP by propionylation, which is tightly linked to intracellular survival. By expressing and purifying PhoP protein in vitro and performing EMSA and protein phosphorylation analyses, We provide evidence that K102 of PhoP is modified by Kpr propionate, which regulates S. Typhi viability in macrophages by decreasing the phosphorylation and DNA-binding ability of PhoP. In conclusion, our study reveals a potential molecular mechanism by which propionate reduces the viability of S. Typhi in macrophages via Kpr.

Salmonella-liberated dietary L-arabinose promotes expansion in superspreaders

The molecular understanding of host-pathogen interactions in the gastrointestinal (GI) tract of superspreader hosts is incomplete. In a mouse model of chronic, asymptomatic Salmonella enterica serovar Typhimurium (S. Tm) infection, we performed untargeted metabolomics on the feces of mice and found that superspreader hosts possess distinct metabolic signatures compared with non-superspreaders, including differential levels of L-arabinose. RNA-seq on S. Tm from superspreader fecal samples showed increased expression of the L-arabinose catabolism pathway in vivo. By combining bacterial genetics and diet manipulation, we demonstrate that diet-derived L-arabinose provides S. Tm a competitive advantage in the GI tract, and expansion of S. Tm in the GI tract requires an alpha-N-arabinofuranosidase that liberates L-arabinose from dietary polysaccharides. Ultimately, our work shows that pathogen-liberated L-arabinose from the diet provides a competitive advantage to S. Tm in vivo. These findings propose L-arabinose as a critical driver of S. Tm expansion in the GI tracts of superspreader hosts.

Genomic Investigation of Salmonella Typhi in Hong Kong Revealing the Predominance of Genotype 3.2.2 and the First Case of an Extensively Drug-Resistant H58 Genotype

Typhoid fever is a notable disease in Hong Kong. We noticed two local cases of typhoid fever caused by Salmonella Typhi within a two-week period in late 2022, which had no apparent epidemiological linkage except for residing in the same region of Hong Kong. A phylogenetic study of Salmonella Typhi isolates from Hong Kong Island from 2020 to 2022 was performed, including a whole-genome analysis, the typing of plasmids, and the analysis of antibiotic-resistance genes (ARGs), to identify the dominant circulating strain and the spread of ARGs. A total of seven isolates, from six local cases and an imported case, were identified from positive blood cultures in two hospitals in Hong Kong. Five antibiotic-sensitive strains of genotype 3.2.2 were found, which clustered with another 30 strains originating from Southeast Asia. Whole-genome sequencing revealed clonal transmission between the two index cases. The remaining two local cases belong to genotype 2.3.4 and genotype 4.3.1.1.P1 (also known as the H58 lineage). The genotype 4.3.1.1.P1 strain has an extensively drug-resistant (XDR) phenotype (co-resistance to ampicillin, chloramphenicol, ceftriaxone, ciprofloxacin, and co-trimoxazole). Although the majority of local strains belong to the non-H58 genotype 3.2.2 with a low degree of antibiotic resistance, the introduction of XDR strains with the global dissemination of the H58 lineage remains a concern.

A Phase II/III, Multicenter, Observer-blinded, Randomized, Non-inferiority and Safety, study of typhoid conjugate vaccine (EuTCV) compared to Typbar-TCV® in healthy 6 Months-45 years aged participants

The typhoid conjugate vaccine (TCV) ensures a long-lasting protective immune response, requires fewer doses and is fit for children under 2 years of age. From Phase I study, EuTCV displayed considerable immunogenicity and reliable safety, thus endorsing further examination in Phase II/III trials. Therefore, a clinical Phase II/III study (NCT04830371) was conducted to evaluate its efficacy in healthy Filipino participants aged 6 months to 45 years through administration of the test vaccine (Arm A, B, and C) or comparator vaccine Typbar-TCV® (Arm D). Sera samples were collected pre-vaccination (Visit 1) and post-vaccination (Visit 4, Day 28) to assess the immunogenicity of EuTCV and Typbar-TCV®. During the study, participants were regularly monitored through scheduled visits to the clinic to report any adverse events associated with the vaccine. For vaccine safety, the proportion of solicited and unsolicited Treatment-Emergent Adverse Events was all comparable between EuTCV and Typbar-TCV® groups. A single dose of EuTCV produced seroconversion in 99.4% of treated participants, with seroconversion rates non-inferior to that of Typbar-TCV®. Batch-to-batch consistency was concluded based on the 90% Confidence Interval of the geometric mean ratio (EuTCV Arm A, B, and C) at Week 4, lying within the equivalence margin of 0.5 to 2.0 for all batches. Results from this Phase II/III clinical trial of EuTCV in healthy volunteers show comparable safety and considerable immunogenicity, compared to Typbar-TCV®, meeting the objectives of this pivotal study. ClinicalTrials.gov registration number: NCT04830371.

Recent advances in the diagnosis and management of typhoid fever in Africa: A review

Typhoid fever, a classical disease of enteric origin caused by Salmonella species of bacteria, is among the most important diseases threatening public health in Africa. The African continent is a marker for both low resources within the healthcare system and poor disease control policy formulations in managing endemic infectious diseases. Since the colonial era, the Widal serological test has been used to confirm typhoid fever in Africa, however recent studies recommend blood culture, and when blood culture cannot be obtained, clinical findings, laboratory Widal test confirmation, and ruling out other febrile illnesses as confirmatory pathway to diagnose typhoid fever in Africa. Managing typhoid fever relies on antimicrobials. In 1980s chloramphenicol was the medication of choice. Years later, amoxicillin and co-trimoxazole were adopted. However, the instantaneous rise of resistant strains of Salmonella enterica confers an important challenge to treat the burdensome enteric fever. The current treatment algorithm of typhoid fever in Africa relies significantly on the use of fluoroquinolones, macrolides, and cephalosporins. Developed nations have successfully addressed and controlled typhoid fever via improvement in accessing safe water and food, better sanitary and hygienic behaviours, and vaccines development. Nevertheless, there is significant evidence to infer improvement in the diagnosis management of typhoid fever over the last few decades, and efforts are underway to control the disease spread in Africa. This review aims to provide an overview of the latest developments in typhoid fever diagnosis and management in Africa and provide key recommendations for a coordinated approach to mitigate typhoid in the continent.

ANTIBIOTIC RESISTANCE OF SALMONELLA TYPHI CARRIER ASSOCIATED WITH GALL BLADDER CHRONIC INFECTION IN AL-NAJAF PROVINCE

OBJECTIVE

The aim: This study was undertaken to identify antibiotic resistance of Salmonella Typhi in specimens of gall bladder tissue after cholecystectomy.

PATIENTS AND METHODS

Materials and methods: Salmonella Typhi identification from the isolates have been depended on morphology of the colony and biochemical tests as a first step in identification while final identification has been achieved by the automated VITEK-2 compact system then PCR technique.

RESULTS

Results: Depending to finding via the VITEK tests and PCR technique and thirty-five Salmonella Typhi sample have been obtained. This research shown that about 35 (70%) positive result contains, 12 (34.3%) isolates was positive from stool and 23(65.7%) from gall bladder tissue. The results revealed difference in S. Typhi resistance to some antibiotics, where S. Typhi has wide-ranging sensitivity: 35 (100%) to Cefepime, Cefixime and Ciprofloxacin and revealed great sensitivity 22 (62.8%) to Ampicillin. S. Typhi isolates proved extremely resistant 19 (54.2%) and 25 (71.4%) to Trimethoprim/Sulphamethoxazole and Chloramphenicol respectively. Increment in the rate of Salmonella that has multidrug resistance to chloramphenicol, ampicillin, furazolidonecotrimoxazole, streptomycin, and tetracycline is a developing problem and worldwide worry matte.

CONCLUSION

Conclusions: Resistant forms of Salmonella enteric serotype Typhi were detected with increment in the rate of multidrug resistance to chloramphenicol, ampicillin, and tetracycline so currently, Cefepime, Cefixime and Ciprofloxacin and revealed great sensitivity and have become the mainstay of treatment. Challenging difficult which rises in this study is the extend of Multidrug resistant strain (MDR) of S. Typhi.

Mohammed A, Mohammed Flyyiah T. Whole-genome sequencing of Aminoglycoside nucleotidyltransferase aadA1 in patients with typhoid

S. typhi is causes typhoid in Iraq and developing countries. The abuse of antibiotics make the patient infected with S. typhi wich is resistant to many antibiotics. Aims of the study: Molecular and phylogenetic tree of genomic resistance genes associated Aminoglycoside nucleotidyltransferase (aad-A1), and detection mutation occur in aadA1 gene. Disc diffusion method and VITEK2 compact system to detect the resistance of S.typhi to 11 antibiotics and using the PCR technique to detect the prevalence of aadA1 resistance gene. The genomic DNA extracted from all S. typhi isolated harboring resistance gene. The prevalence of the aadA1 gene was 12(24%) from all S. typhi isolates and the presence of a silent mutation in sample number 2 Iraqi isolate. The first isolate (MW805237.1) was almost just like the isolates of each of the countries Korea, Iran Iran, India, and Madagascar, but The second Iraqi isolate (MW805238.1) was the share of congruence between them at 99% at position G. The aadA1 gene was present in S. typhi isolated from blood, the stool of human, and the detected mutation has no effect.

Affinity of cefotiam for the alternative penicillin binding protein PBP3SAL used by Salmonella inside host eukaryotic cells

BACKGROUND

Following the invasion of eukaryotic cells, Salmonella enterica serovar Typhimurium replaces PBP2/PBP3, main targets of β-lactam antibiotics, with PBP2SAL/PBP3SAL, two homologue peptidoglycan synthases absent in Escherichia coli. PBP3SAL promotes pathogen cell division in acidic environments independently of PBP3 and shows low affinity for β-lactams that bind to PBP3 such as aztreonam, cefepime, cefotaxime, ceftazidime, ceftriaxone, cefuroxime and cefalotin.

OBJECTIVES

To find compounds with high affinity for PBP3SAL to control Salmonella intracellular infections.

METHODS

An S. Typhimurium ΔPBP3 mutant that divides using PBP3SAL and its parental wild-type strain, were exposed to a library of 1520 approved drugs in acidified (pH 4.6) nutrient-rich LB medium. Changes in optical density associated with cell filamentation, a read-out of blockage in cell division, were monitored. Compounds causing filamentation in the ΔPBP3 mutant but not in wild-type strain-the latter strain expressing both PBP3 and PBP3SAL in LB pH 4.6-were selected for further study. The bactericidal effect due to PBP3SAL inhibition was evaluated in vitro using a bacterial infection model of cultured fibroblasts.

RESULTS

The cephalosporin cefotiam exhibited higher affinity for PBP3SAL than for PBP3 in bacteria growing in acidified LB pH 4.6 medium. Cefotiam also proved to be effective against intracellular Salmonella in a PBP3SAL-dependent manner. Conversely, cefuroxime, which has higher affinity for PBP3, showed decreased effectiveness in killing intracellular Salmonella.

CONCLUSIONS

Antibiotics with affinity for PBP3SAL, like the cephalosporin cefotiam, have therapeutic value for treating Salmonella intracellular infections.

Implementation of an outbreak response vaccination campaign with typhoid conjugate vaccine – Harare, Zimbabwe, 2019

Introduction

Typhoid fever is a public-health problem in Harare, the capital city of Zimbabwe, with seasonal outbreaks occurring annually since 2010. In 2019, the Ministry of Health and Child Care (MOHCC) organized the first typhoid conjugate vaccination campaign in Africa in response to a recurring typhoid outbreak in a large urban setting.

Method

As part of a larger public health response to a typhoid fever outbreak in Harare, Gavi approved in September 2018 a MOHCC request for 340,000 doses of recently prequalified Typbar-TCV to implement a mass vaccination campaign. To select areas for the campaign, typhoid fever surveillance data from January 2016 until June 2018 was reviewed. We collected and analyzed information from the MOHCC and its partners to describe the vaccination campaign planning, implementation, feasibility, administrative coverage and financial costs.

Results

The campaign was conducted in nine high-density suburbs of Harare over eight days in February–March 2019 and targeted all children aged 6 months–15 years; however, the target age range was extended up to 45 years in one suburb due to the past high attack rate among adults. A total of 318,698 people were vaccinated, resulting in overall administrative coverage of 85.4 percent. More than 750 community volunteers and personnel from the MOHCC and the Ministry of Education were trained and involved in social mobilization and vaccination activities. The MOHCC used a combination of vaccination strategies (i.e., fixed and mobile immunization sites, a creche and school-based strategy, and door-to-door activities). Financial costs were estimated at US$ 2.39 per dose, including the vaccine and vaccination supplies (US$ 0.79 operational costs per dose excluding vaccine and vaccination supplies).

Conclusion

A mass targeted campaign in densely populated urban areas in Harare, using the recently prequalified typhoid conjugate vaccine, was feasible and achieved a high overall coverage in a short period of time.

The evolutionary diversification of the Salmonella artAB toxin locus

Salmonella enterica is a diverse species of bacterial pathogens comprised of >2,500 serovars with variable host ranges and virulence properties. Accumulating evidence indicates that two AB₅-type toxins, typhoid toxin and ArtAB toxin, contribute to the more severe virulence properties of the Salmonella strains that encode them. It was recently discovered that there are two distinct types of artAB-like genetic elements in Salmonella: those that encode ArtAB toxins (artAB elements) and those in which the artA gene is degraded and the ArtB homolog, dubbed PltC, serves as an alternative delivery subunit for typhoid toxin (pltC elements). Here, we take a multifaceted approach to explore the evolutionary diversification of artAB-like genetic elements in Salmonella. We identify 7 subtypes of ArtAB toxins and 4 different PltC sequence groups that are distributed throughout the Salmonella genus. Both artAB and pltC are encoded within numerous diverse prophages, indicating a central role for phages in their evolutionary diversification. Genetic and structural analyses revealed features that distinguish pltC elements from artAB and identified evolutionary adaptations that enable PltC to efficiently engage typhoid toxin A subunits. For both pltC and artAB, we find that the sequences of the B subunits are especially variable, particularly amongst amino acid residues that fine tune the chemical environment of their glycan binding pockets. This study provides a framework to delineate the remarkably complex collection of Salmonella artAB/pltC-like genetic elements and provides a window into the mechanisms of evolution for AB₅-type toxins.

Treatment of enteric fever (typhoid and paratyphoid fever) with cephalosporins

BACKGROUND

Typhoid and paratyphoid (enteric fever) are febrile bacterial illnesses common in many low- and middle-income countries. The World Health Organization (WHO) currently recommends treatment with azithromycin, ciprofloxacin, or ceftriaxone due to widespread resistance to older, first-line antimicrobials. Resistance patterns vary in different locations and are changing over time. Fluoroquinolone resistance in South Asia often precludes the use of ciprofloxacin. Extensively drug-resistant strains of enteric fever have emerged in Pakistan. In some areas of the world, susceptibility to old first-line antimicrobials, such as chloramphenicol, has re-appeared. A Cochrane Review of the use of fluoroquinolones and azithromycin in the treatment of enteric fever has previously been undertaken, but the use of cephalosporins has not been systematically investigated and the optimal choice of drug and duration of treatment are uncertain.

OBJECTIVES

To evaluate the effectiveness of cephalosporins for treating enteric fever in children and adults compared to other antimicrobials.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL, MEDLINE, Embase, LILACS, the WHO ICTRP and ClinicalTrials.gov up to 24 November 2021. We also searched reference lists of included trials, contacted researchers working in the field, and contacted relevant organizations.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in adults and children with enteric fever that compared a cephalosporin to another antimicrobial, a different cephalosporin, or a different treatment duration of the intervention cephalosporin. Enteric fever was diagnosed on the basis of blood culture, bone marrow culture, or molecular tests.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were clinical failure, microbiological failure and relapse. Our secondary outcomes were time to defervescence, duration of hospital admission, convalescent faecal carriage, and adverse effects. We used the GRADE approach to assess certainty of evidence for each outcome.

MAIN RESULTS

We included 27 RCTs with 2231 total participants published between 1986 and 2016 across Africa, Asia, Europe, the Middle East and the Caribbean, with comparisons between cephalosporins and other antimicrobials used for the treatment of enteric fever in children and adults. The main comparisons are between antimicrobials in most common clinical use, namely cephalosporins compared to a fluoroquinolone and cephalosporins compared to azithromycin. Cephalosporin (cefixime) versus fluoroquinolones Clinical failure, microbiological failure and relapse may be increased in patients treated with cefixime compared to fluoroquinolones in three small trials published over 14 years ago: clinical failure (risk ratio (RR) 13.39, 95% confidence interval (CI) 3.24 to 55.39; 2 trials, 240 participants; low-certainty evidence); microbiological failure (RR 4.07, 95% CI 0.46 to 36.41; 2 trials, 240 participants; low-certainty evidence); relapse (RR 4.45, 95% CI 1.11 to 17.84; 2 trials, 220 participants; low-certainty evidence). Time to defervescence in participants treated with cefixime may be longer compared to participants treated with fluoroquinolones (mean difference (MD) 1.74 days, 95% CI 0.50 to 2.98, 3 trials, 425 participants; low-certainty evidence). Cephalosporin (ceftriaxone) versus azithromycin Ceftriaxone may result in a decrease in clinical failure compared to azithromycin, and it is unclear whether ceftriaxone has an effect on microbiological failure compared to azithromycin in two small trials published over 18 years ago and in one more recent trial, all conducted in participants under 18 years of age: clinical failure (RR 0.42, 95% CI 0.11 to 1.57; 3 trials, 196 participants; low-certainty evidence); microbiological failure (RR 1.95, 95% CI 0.36 to 10.64, 3 trials, 196 participants; very low-certainty evidence). It is unclear whether ceftriaxone increases or decreases relapse compared to azithromycin (RR 10.05, 95% CI 1.93 to 52.38; 3 trials, 185 participants; very low-certainty evidence). Time to defervescence in participants treated with ceftriaxone may be shorter compared to participants treated with azithromycin (mean difference of -0.52 days, 95% CI -0.91 to -0.12; 3 trials, 196 participants; low-certainty evidence). Cephalosporin (ceftriaxone) versus fluoroquinolones It is unclear whether ceftriaxone has an effect on clinical failure, microbiological failure, relapse, and time to defervescence compared to fluoroquinolones in three trials published over 28 years ago and two more recent trials: clinical failure (RR 3.77, 95% CI 0.72 to 19.81; 4 trials, 359 participants; very low-certainty evidence); microbiological failure (RR 1.65, 95% CI 0.40 to 6.83; 3 trials, 316 participants; very low-certainty evidence); relapse (RR 0.95, 95% CI 0.31 to 2.92; 3 trials, 297 participants; very low-certainty evidence) and time to defervescence (MD 2.73 days, 95% CI -0.37 to 5.84; 3 trials, 285 participants; very low-certainty evidence). It is unclear whether ceftriaxone decreases convalescent faecal carriage compared to the fluoroquinolone gatifloxacin (RR 0.18, 95% CI 0.01 to 3.72; 1 trial, 73 participants; very low-certainty evidence) and length of hospital stay may be longer in participants treated with ceftriaxone compared to participants treated with the fluoroquinolone ofloxacin (mean of 12 days (range 7 to 23 days) in the ceftriaxone group compared to a mean of 9 days (range 6 to 13 days) in the ofloxacin group; 1 trial, 47 participants; low-certainty evidence).

AUTHORS' CONCLUSIONS

Based on very low- to low-certainty evidence, ceftriaxone is an effective treatment for adults and children with enteric fever, with few adverse effects. Trials suggest that there may be no difference in the performance of ceftriaxone compared with azithromycin, fluoroquinolones, or chloramphenicol. Cefixime can also be used for treatment of enteric fever but may not perform as well as fluoroquinolones.  We are unable to draw firm general conclusions on comparative contemporary effectiveness given that most trials were small and conducted over 20 years previously. Clinicians need to take into account current, local resistance patterns in addition to route of administration when choosing an antimicrobial.

Super Shedding in Enteric Pathogens: A Review

Super shedding occurs when a small number of individuals from a given host population shed high levels of a pathogen. Beyond this general definition, various interpretations of the shedding patterns have been proposed to identify super shedders, leading to the description of the super shedding phenomenon in a wide range of pathogens, in particular enteric pathogens, which are of considerable interest. Several underlying mechanisms may explain this observation, including factors related to the environment, the gut microbiota, the pathogen itself (i.e., genetic polymorphism), and the host (including immune factors). Moreover, data suggest that the interplay of these parameters, in particular at the host-pathogen-gut microbiota interface, is of crucial importance for the determination of the super shedding phenotype in enteric pathogens. As a phenomenon playing an important role in the epidemics of enteric diseases, the evidence of super shedding has highlighted the need to develop various control strategies.

Comparison of Single vs Combination Drug Therapy in Extensively Drug Resistant Salmonella typhi: An Observational Study from Pakistan

Introduction

Antibiotic resistance has become a significant problem in typhoid fever due to the emergence of extensively drug resistant (XDR) Salmonella enterica serovar typhi. In Pakistan, an outbreak of ceftriaxone-resistant typhoid was first reported in November 2016.

Methods

A retrospective chart review was conducted at Liaquat National Hospital and Medical University, in Karachi, Pakistan. Patient records were identified from the microbiology laboratory data of all admitted patients who had blood culture positive for XDR Salmonella typhi from January 2017 to December 2019.

Results

Out of 254 patients, 179 (70%) were male with an average age of 11.7 ± 10.9 years. Around 190 (74%) patients were treated with combination therapy, 126 (49%) were given azithromycin and meropenem and 61 (24%) received azithromycin and imipenem. A total of 64 (25%) patients received single drug therapy, 33 (12%) were given azithromycin, 23 (9%) meropenem, and 8 (3%) imipenem. Analysis indicated that single drug therapy resulted in an earlier onset of defervescence compared with combination therapy (5.03±2.98 days vs 3.45±2.48 days; P <0.001), with a decreased occurrence of pancytopenia (P <0.001).

Conclusion

Single antimicrobial therapy achieved defervescence earlier than combination therapy, with carbapenems performing better than azithromycin.

Understanding the Mechanism of Antimicrobial Resistance and Pathogenesis of Salmonella enterica Serovar Typhi

Salmonella enterica serovar Typhi (S. Typhi) is a Gram-negative pathogen that causes typhoid fever in humans. Though many serotypes of Salmonella spp. are capable of causing disease in both humans and animals alike, S. Typhi and S. Paratyphi are common in human hosts only. The global burden of typhoid fever is attributable to more than 27 million cases each year and approximately 200,000 deaths worldwide, with many regions such as Africa, South and Southeast Asia being the most affected in the world. The pathogen is able to cause disease in hosts by evading defense systems, adhesion to epithelial cells, and survival in host cells in the presence of several virulence factors, mediated by virulence plasmids and genes clustered in distinct regions known as Salmonella pathogenicity islands (SPIs). These factors, coupled with plasmid-mediated antimicrobial resistance genes, enable the bacterium to become resistant to various broad-spectrum antibiotics used in the treatment of typhoid fever and other infections caused by Salmonella spp. The emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains in many countries of the world has raised great concern over the rise of antibiotic resistance in pathogens such as S. Typhi. In order to identify the key virulence factors involved in S. Typhi pathogenesis and infection, this review delves into various mechanisms of virulence, pathogenicity, and antimicrobial resistance to reinforce efficacious disease management.

Distribution of Ciprofloxacin- and Azithromycin-Resistant Genes among Salmonella Typhi Isolated from Human Blood

Context

Salmonella Typhi has developed resistance to different groups of antibiotics.

Aims

The purpose of the present study was to assess the distribution of ciprofloxacin- and azithromycin-resistant genes among Salmonella Typhi isolated from human blood.

Settings and Design

This cross-sectional study was conducted in the Department of Microbiology of a tertiary care hospital in Bangladesh from July 2019-June 2020.

Subjects and Methods

Clinically suspected enteric fever patients, irrespective of age and gender, who attended the laboratory of the Department of Microbiology and outpatient department of Medicine of tertiary care hospital. Blood culture and sensitivity tests were done. The positive growth of Salmonella Typhi was identified by Gram staining, colony morphology, and biochemical test. Then, Salmonella Typhi was identified by using Salmonella-specific antisera. Final identification was made by using 16s rRNA by polymerase chain reaction (PCR). PCR was also done to detect quinolone and azithromycin resistance genes.

Results

A total number of 83 samples yielded positive cultures, of which 50 isolated organisms were identified as Salmonella species; however, among these isolates, Salmonella Typhi was detected in 40 (48.2%) isolates. Among 12 ciprofloxacin-resistant isolates, 8 (66.67%) were positive for the gyrA gene, 1 (8.33%) was positive for the qnrB gene and qnrS gene, 2 (16.67%) were positive for aac (6´)-Ib-cr. Among 12 azithromycin-resistant isolates, 2 (16.66%) were positive for mphA and mefA genes, respectively.

Conclusion

In conclusion, the gyrA, aac (6´)-Ib-cr, mphA, and mefA genes are found for the first time in tertiary care hospitals from the quinolones and azithromycin-resistant Salmonella Typhi.

Concurrent Typhoid Fever and Dengue Hemorrhagic Fever: A Case Report

Dengue virus can co-infect with a number of viruses, bacteria, and parasites of which dengue malaria co-infection is most well-known. We report a rare case of dengue virus co-infection with typhoid fever and the development of dengue hemorrhagic fever (DHF) during a dengue outbreak. The second spike of high-grade fever following initial defervescence with antibiotic therapy, hemorrhagic manifestations, new onset leucopenia and thrombocytopenia, and evidence of plasma leakage raised suspicion of DHF. Diagnosis of dengue co-infection was made by seroconversion for anti-dengue immunoglobulin M (IgM) antibodies by enzyme-linked immunosorbent assay (ELISA) on the seventh day of new-onset fever. Early recognition and judicious use of fluid therapy prevented the patient from developing shock and its complications. Prompt diagnosis, early recognition of plasma leakage, and appropriate management of DHF can reduce morbidity and mortality.

Lipopolysaccharides and outer membrane proteins as main structures involved in complement evasion strategies of non-typhoidal Salmonella strains

Non-typhoidal Salmonella (NTS) infections pose a serious public health problem. In addition to the typical course of salmonellosis, an infection with Salmonella bacteria can often lead to parenteral infections and sepsis, which are particularly dangerous for children, the elderly and immunocompromised. Bacterial resistance to serum is a key virulence factor for the development of systemic infections. Salmonella, as an enterobacterial pathogen, has developed several mechanisms to escape and block the antibacterial effects of the complement system. In this review, we discuss the relevance of outer membrane polysaccharides to the complement evasion mechanisms of NTS strains. These include the influence of the overall length and density of the lipopolysaccharide molecules, modifications of the O-antigen lipopolysaccharide composition and the role of capsular polysaccharides in opsonization and protection of the outer membrane from the lytic action of complement. Additionally, we discuss specific outer membrane protein complement evasion mechanisms, such as recruitment of complement regulatory proteins, blocking assembly of late complement components to form the membrane attack complex and the proteolytic cleavage of complement proteins.

Clinical Characteristics and Antibiotics Sensitivity of Culture Positive Typhoid Fever Patients in Baghdad Teaching Hospital - A Single Center Study

BACKGROUND: Enteric fever caused by Salmonella Typhi is an endemic disease in Iraq. Variations in presentations make it a diagnostic challenge. If untreated or treated inappropriately then it is a serious disease with potentially life-threatening complications. The recent emergence of drug resistant strains of S. Typhi is a rising public health problem and a clinical concern to the physician. AIM: The objectives of the study were to assess and describe the patterns of antimicrobial resistance, clinical characteristics, epidemiological distribution, and complications of typhoid fever. PATIENTS AND METHODS: Fifty cases of typhoid fever (culture proven) were collected during the period from February 2019 to November 2019 in the medical wards of Baghdad Teaching Hospital. Detailed history, physical examination, and laboratory investigations were conducted and statistical analysis of the results was done, prospective observational study was conducted. RESULTS: During the study period, 50 cases of typhoid fever were documented, mean age of presentation was 30.7 ± 12.8, 60% of the cases were male gender, gastrointestinal complications were the most common (90%) followed by hematological complications (71%). Mortality of typhoid fever in our study was 2%. High percentage of resistance to third generation cephalosporins, ciprofloxacin, and azithromycin was found (96%, 56%, and 56%, respectively) while good sensitivity to trimethoprim and meropenem was found (94% and 76%, respectively). Significant association was also found between the development of typhoid fever complications and the presence of anemia, thrombocytopenia, lymphopenia, and eosinopenia. Significant association was also found between the complications and the infection with strains resistant to cephalosporins, ciprofloxacin, and azithromycin. CONCLUSIONS: There is a concerning increase in resistance toward cephalosporins, ciprofloxacin, and azithromycin while meropenem and trimethoprim are emerging as effective drugs. There was high incidence of complications found (84%).Lymphopenia, anemia, eosinopenia, and thrombocytopenia are independent risk factors for the development of complications of typhoid fever.

Outbreak of Typhoid Fever in Children of Urban Vellore: A Report from the Surveillance for Enteric Fever in India Cohort

We report an outbreak of typhoid fever between April and June 2019 in the Surveillance for Enteric Fever in India cohort, a pediatric cohort from four contiguous semi-urban settlements of Vellore in South India. This cohort of children 6 months to 15 years of age was under surveillance from October 2017 to December 2019. A clustering of typhoid cases in the cohort was noted with reference to time, place, and person. The overall typhoid attack rate in the cohort was 0.9%, with the highest attack rate of 1.7% being documented in one of the four areas. The rate of hospitalization and complications in children who were typhoid positive during the outbreak was 28% and 2%, respectively. Given the background of suboptimal water, sanitation, and hygiene, and the risk of typhoid fever outbreaks in these settings, it is imperative that a typhoid vaccine be considered for introduction as a pragmatic preventive approach.

Facility-based disease surveillance and Bayesian hierarchical modeling to estimate endemic typhoid fever incidence, Kilimanjaro Region, Tanzania, 2007–2018

Growing evidence suggests considerable variation in endemic typhoid fever incidence at some locations over time, yet few settings have multi-year incidence estimates to inform typhoid control measures. We sought to describe a decade of typhoid fever incidence in the Kilimanjaro Region of Tanzania. Cases of blood culture confirmed typhoid were identified among febrile patients at two sentinel hospitals during three study periods: 2007–08, 2011–14, and 2016–18. To account for under-ascertainment at sentinel facilities, we derived adjustment multipliers from healthcare utilization surveys done in the hospital catchment area. Incidence estimates and credible intervals (CrI) were derived using a Bayesian hierarchical incidence model that incorporated uncertainty of our observed typhoid fever prevalence, of healthcare seeking adjustment multipliers, and of blood culture diagnostic sensitivity. Among 3,556 total participants, 50 typhoid fever cases were identified. Of typhoid cases, 26 (52%) were male and the median (range) age was 22 (<1–60) years; 4 (8%) were aged <5 years and 10 (20%) were aged 5 to 14 years. Annual typhoid fever incidence was estimated as 61.5 (95% CrI 14.9–181.9), 6.5 (95% CrI 1.4–20.4), and 4.0 (95% CrI 0.6–13.9) per 100,000 persons in 2007–08, 2011–14, and 2016–18, respectively. There were no deaths among typhoid cases. We estimated moderate typhoid incidence (≥10 per 100 000) in 2007–08 and low (<10 per 100 000) incidence during later surveillance periods, but with overlapping credible intervals across study periods. Although consistent with falling typhoid incidence, we interpret this as showing substantial variation over the study periods. Given potential variation, multi-year surveillance may be warranted in locations making decisions about typhoid conjugate vaccine introduction and other control measures.

There is evidence that typhoid fever incidence may vary over time, but there are few longitudinal studies estimating incidence. This is especially true in Sub-Saharan Africa, where recent estimates show wide variation in incidence across different settings, but very limited longitudinal descriptions from those settings. Incidence estimates were generated using facility-based surveillance data from three study periods that was adjusted for health-seeking behavior established through healthcare utilization surveys performed in the catchment area. In addition to coupling facility-based surveillance data with healthcare utilization data, we utilized a Bayesian statistical methodology in order to estimate incidence and characterize uncertainty around the estimates. Our results demonstrate moderate typhoid incidence in 2007–08 and low incidence during 2012–14 and 2016–18, but with overlapping credible intervals across study periods. Our data are consistent with evidence that endemic typhoid may vary substantially over time. Given potential variation, multi-year surveillance may be warranted in locations making decisions about typhoid conjugate vaccine introduction and other control measures.

Genomic epidemiology of Salmonella Typhi in Central Division, Fiji, 2012 to 2016

BACKGROUND

Typhoid fever is endemic in some Pacific Island Countries including Fiji and Samoa yet genomic surveillance is not routine in such settings. Previous studies suggested imports of the global H58 clade of Salmonella enterica var Typhi (Salmonella Typhi) contribute to disease in these countries which, given the MDR potential of H58, does not auger well for treatment. The objective of the study was to define the genomic epidemiology of Salmonella Typhi in Fiji.

METHODS

Genomic sequencing approaches were implemented to study the distribution of 255 Salmonella Typhi isolates from the Central Division of Fiji. We augmented epidemiological surveillance and Bayesian phylogenomic approaches with a multi-year typhoid case-control study to define geospatial patterns among typhoid cases.

FINDINGS

Genomic analyses showed Salmonella Typhi from Fiji resolved into 2 non-H58 genotypes with isolates from the two dominant ethnic groups, the Indigenous (iTaukei) and non-iTaukei genetically indistinguishable. Low rates of international importation of clones was observed and overall, there were very low levels an antibiotic resistance within the endemic Fijian typhoid genotypes. Genomic epidemiological investigations were able to identify previously unlinked case clusters. Bayesian phylodynamic analyses suggested that genomic variation within the larger endemic Salmonella Typhi genotype expanded at discreet times, then contracted.

INTERPRETATION

Cyclones and flooding drove 'waves' of typhoid outbreaks in Fiji which, through population aggregation, poor sanitation and water safety, and then mobility of the population, spread clones more widely. Minimal international importations of new typhoid clones suggest that targeted local intervention strategies may be useful in controlling endemic typhoid infection. These findings add to our understanding of typhoid transmission networks in an endemic island country with broad implications, particularly across Pacific Island Countries.

FUNDING

This work was supported by the Coalition Against Typhoid through the Bill and Melinda Gates Foundation [grant number OPP1017518], the Victorian Government, the National Health and Medical Research Council Australia, the Australian Research Council, and the Fiji Ministry of Health and Medical Services.

Outpatient management of uncomplicated enteric fever: A case series of 93 patients from the Hospital of Tropical Diseases, London

OBJECTIVES

Enteric fever is predominantly managed as an outpatient condition in endemic settings but there is little evidence to support this approach in non-endemic settings. This study aims to review the outcomes of outpatients treated for enteric fever at the Hospital of Tropical Diseases in London, UK.

METHODS

We conducted a retrospective analysis of all patients with confirmed enteric fever between August 2009 and September 2020. Demographic, clinical, laboratory and microbiological data were collected and compared between the inpatient and outpatient populations. Outcomes investigated were complicated enteric fever, treatment failure and relapse.

RESULTS

Overall, 93 patients (59% male, median age 31) were identified with blood and/or stool culture confirmed enteric fever and 49 (53%) of these were managed as outpatients. The commonest empirical treatment for outpatients was azithromycin (70%) and for inpatients was ceftriaxone (84%). Outpatients were more likely than inpatients to receive only one antibiotic (57% vs 19%, p < 0.01) and receive a shorter duration of antibiotics (median 7 vs 11 days, p <0.01). There were no cases of complicated disease or relapse in either the inpatient or outpatient groups. There was one treatment failure in the outpatient group. Azithromycin was well-tolerated with no reported side effects.

CONCLUSIONS

Our findings suggest that outpatient management of uncomplicated imported enteric fever is safe and effective with the use of oral azithromycin. Careful monitoring of patients is recommended as treatment failure can occur.

The CRISPR-Cas System Differentially Regulates Surface-Attached and Pellicle Biofilm in Salmonella enterica Serovar Typhimurium

The CRISPR-Cas mediated regulation of biofilm by Salmonella enterica serovar Typhimurium was investigated by deleting CRISPR-Cas components ΔcrisprI, ΔcrisprII, ΔΔcrisprI crisprII, and Δcas op. We determined that the system positively regulates surface biofilm while inhibiting pellicle biofilm formation. Results of real-time PCR suggest that the flagellar (fliC, flgK) and curli (csgA) genes were repressed in knockout strains, causing reduced surface biofilm. The mutants displayed altered pellicle biofilm architecture. They exhibited bacterial multilayers and a denser extracellular matrix with enhanced cellulose and less curli, ergo weaker pellicles than those of the wild type. The cellulose secretion was more in the knockout strains due to the upregulation of bcsC, which is necessary for cellulose export. We hypothesized that the secreted cellulose quickly integrates into the pellicle, leading to enhanced pellicular cellulose in the knockout strains. We determined that crp is upregulated in the knockout strains, thereby inhibiting the expression of csgD and, hence, also of csgA and bcsA. The conflicting upregulation of bcsC, the last gene of the bcsABZC operon, could be caused by independent regulation by the CRISPR-Cas system owing to a partial match between the CRISPR spacers and bcsC gene. The cAMP-regulated protein (CRP)-mediated regulation of the flagellar genes in the knockout strains was probably circumvented through the regulation of yddx governing the availability of the sigma factor σ²⁸ that further regulates class 3 flagellar genes (fliC, fljB, and flgK). Additionally, the variations in the lipopolysaccharide (LPS) profile and expression of LPS-related genes (rfaC, rfbG, and rfbI) in knockout strains could also contribute to the altered pellicle architecture. Collectively, we establish that the CRISPR-Cas system differentially regulates the formation of surface-attached and pellicle biofilm.

IMPORTANCE In addition to being implicated in bacterial immunity and genome editing, the CRISPR-Cas system has recently been demonstrated to regulate endogenous gene expression and biofilm formation. While the function of individual cas genes in controlling Salmonella biofilm has been explored, the regulatory role of CRISPR arrays in biofilm is less studied. Moreover, studies have focused on the effects of the CRISPR-Cas system on surface-associated biofilms, and comprehensive studies on the impact of the system on pellicle biofilm remain an unexplored niche. We demonstrate that the CRISPR array and cas genes modulate the expression of various biofilm genes in Salmonella, whereby surface and pellicle biofilm formation is distinctively regulated.

Salmonella enterica subsp. II serovar 4,5,12:a:- may cause gastroenteritis infections in humans

Some serovars of Salmonella are not or rare found to cause salmonellosis in human. In our clinic-based surveillance, three rare Salmonella 4,5,12:a:- strains were recovered from three patients with diarrhea. To explore their genetic and epidemiological characteristics and pathogenesis, we conducted whole-genome sequencing, in vitro invasion assays in mammalian cells, and in vivo virulence assays in an animal model. The three isolates had indistinguishable molecular patterns and similar genome sequences, and clustered together with an isolate from edible fish traded among countries. The isolates had biochemical reactions identical with those of Salmonella subspecies enterica but belonged to subspecies salamae according to genome phylogeny, revealing a new serovar, S. enterica subsp. II serovar 4,5,12:a:-. The strains contained multiple virulence genes, elicited temporary bacteremia and enteritidis and caused cell damage in the mouse liver and cecum. This study provides evidence that this new Salmonella salamae serovar can infect humans and cause clusters of cases, and whole-genome sequencing detection and surveillance of Salmonella can help to accurately define Salmonella classification and clonality, improve diagnosis, facilitate outbreak detection and aid in the source tracing of salmonellosis epidemics.

The Complex Mechanism of the Salmonella typhi Biofilm Formation That Facilitates Pathogenicity: A Review

Salmonella enterica serovar Typhi (S. typhi) is an intracellular pathogen belonging to the Enterobacteriaceae family, where biofilm (aggregation and colonization of cells) formation is one of their advantageous traits. Salmonella typhi is the causative agent of typhoid fever in the human body and is exceptionally host specific. It is transmitted through the fecal-oral route by consuming contaminated food or water. This subspecies is quite intelligent to evade the innate detection and immune response of the host body, leading to systemic dissemination. Consequently, during the period of illness, the gallbladder becomes a harbor and may develop antibiotic resistance. Afterwards, they start contributing to the continuous damage of epithelium cells and make the host asymptomatic and potential carriers of this pathogen for an extended period. Statistically, almost 5% of infected people with Salmonella typhi become chronic carriers and are ready to contribute to future transmission by biofilm formation. Biofilm development is already recognized to link with pathogenicity and plays a crucial role in persistency within the human body. This review seeks to discuss some of the crucial factors related to biofilm development and its mechanism of interaction causing pathogenicity. Understanding the connections between these things will open up a new avenue for finding therapeutic approaches to combat pathogenicity.

Typhoid toxin sorting and exocytic transport from Salmonella Typhi-infected cells

Typhoid toxin is an essential virulence factor for Salmonella Typhi, the cause of typhoid fever in humans. This toxin has an unusual biology in that it is produced by Salmonella Typhi only when located within host cells. Once synthesized, the toxin is secreted to the lumen of the Salmonella-containing vacuole from where it is transported to the extracellular space by vesicle carrier intermediates. Here, we report the identification of the typhoid toxin sorting receptor and components of the cellular machinery that packages the toxin into vesicle carriers, and exports it to the extracellular space. We found that the cation-independent mannose-6-phosphate receptor serves as typhoid toxin sorting receptor and that the coat protein COPII and the GTPase Sar1 mediate its packaging into vesicle carriers. Formation of the typhoid toxin carriers requires the specific environment of the Salmonella Typhi-containing vacuole, which is determined by the activities of specific effectors of its type III protein secretion systems. We also found that Rab11B and its interacting protein Rip11 control the intracellular transport of the typhoid toxin carriers, and the SNARE proteins VAMP7, SNAP23, and Syntaxin 4 their fusion to the plasma membrane. Typhoid toxin's cooption of specific cellular machinery for its transport to the extracellular space illustrates the remarkable adaptation of an exotoxin to exert its function in the context of an intracellular pathogen.

Identification of a Host-Targeted Compound to Control Typhoid Fever

Typhoid fever is caused primarily by the enteric microbe Salmonella enterica serovar Typhi and remains a major global health problem with approximately 14 million new infections and 136,000 fatalities annually. While there are antibiotic options available to treat the disease, the global increase in multidrug-resistant strains necessitates alternative therapeutic options. Host-targeted therapeutics present a promising anti-infective strategy against intracellular bacterial pathogens. A cell-based assay identified a compound that inhibits Salmonella proliferation in infected cells, 2-(3-hydroxypropyl)-1-(3-phenoxyphenyl)-1,2-dihydrochromeno[2,3-c]pyrrole-3,9-dione (KH-1), which is devoid of direct activity against Salmonella. The compound inhibits the growth of both antibiotic-sensitive and -resistant Salmonella strains inside macrophages and reduces lactate dehydrogenase (LDH) release from Salmonella-infected cells. Subsequent screening of KH-1 commercial analogs identified 2-(4-fluorobenzyl)-1-(3-phenoxyphenyl)-1,2-dihydrochromeno[2,3-c] pyrrole-3,9-dione (KH-1-2), which is more effective in controlling Salmonella growth inside macrophages. In vitro KH-1-2 treatment of Salmonella infection resulted in an 8- to 10-fold reduction in bacterial load in infected macrophages. In combination with suboptimal ciprofloxacin treatment, KH-1-2 further reduces Salmonella growth inside macrophages. The toxicity and efficacy of KH-1-2 in controlling Salmonella infection were examined in vivo using a mouse model of typhoid fever. No significant compound-related clinical signs and histological findings of the liver, spleen, or kidney were observed from uninfected mice that were intraperitoneally treated with KH-1-2. KH-1-2 significantly protected mice from a lethal dose of infection by an antibiotic-resistant Salmonella strain. Thus, our study provides support that this is a promising lead compound for the development of a novel host-targeted therapeutic agent to control typhoid fever.

IMPORTANCESalmonella spp. cause significant morbidity and mortality worldwide. Typhoidal spp. (e.g., S. Typhi) cause a systemic disease typically treated with antibiotics. However, growing antibiotic resistance is resulting in increased treatment failures. We screened a compound library for those that would reduce Salmonella-induced macrophage toxicity, identifying compound KH-1. KH-1 has no direct effects on the bacteria but limits Salmonella survival in macrophages and protects against lethal infection in a mouse model of typhoid fever. A suboptimal concentration of ciprofloxacin worked in conjunction with the compound to further decrease Salmonella survival in macrophages. An analog (KH-1-2) was identified that possessed increased activity in vitro in macrophages and in vivo against both antibiotic-sensitive and -resistant strains. Thus, we report the identification of a lead compound that may be a useful scaffold as a host-directed antimicrobial against typhoid fever.

Typhoid in Pakistan: Challenges, Efforts, and Recommendations

Typhoid, and its extra drug resistant form which is highly prevalent Pakistan, is increasing the burden on healthcare through multiple factors. These range from lack of sanitation, the collapsing economy, and poor access to clean drinking water which have made it arduous for the government and various other organizations in containing it. With the COVID-19 pandemic, treatment of typhoid became a challenge as focus was driven towards limiting the COVID-19 spread, and hence preferential use of antibiotics such as azithromycin may limit future empirical antibiotic therapy for typhoid. Socioeconomic disparities and geographical as well as demographic barriers further limit access to appropriate typhoid management. Lastly, illiteracy and self-medication with antibiotics may predispose Pakistan to another outbreak of typhoid. These concerns, although largely unaddressed effectively, need immediate action. Previously, the government and international organizations have made efforts to control the spread through the introduction of TCV as a part of EPI and awareness, additional improvements are needed. These include: improving access to telemedicine in rural areas, extensive vaccination programs, and routine awareness programs especially in schools.

Repurposing of FDA approved drugs against Salmonella enteric serovar Typhi by targeting dihydrofolate reductase: an in silico study

Drug-resistant Salmonella enteric serovar Typhi (S. Typhi) poses a vital public health issue. To overcome drug resistance issues, the development of effective drugs with novel mechanism(s) of action is required. In this regard, drug repurposing is a viable alternative approach to find novel drugs to overcome drug resistance. Therefore, a FDA-approved-drug-library containing 1930 drugs was analyzed against the dihydrofolate reductase (DHFR) of S. Typhi using deep learning regression algorithms. Initially, a total of 500 compounds were screened, followed by rescreening by molecular docking. Further, from screened compounds by molecular docking, the top eight compounds were subjected to molecular dynamics (MD) simulation. Analysis of MD simulation resulted in four potential compounds, namely; Duvelisib, Amenamevir, Lifitegrast and Nilotinib against the DHFR enzyme. During the MD simulation, these four drugs achieved good stability during the 100 ns trajectory period at 300 K. Further to know the insights of the complex's stability, we calculated RMSF, RG, SASA and interaction energy for the last 60 ns trajectory period because all complexes showed the stability after 40 ns trajectory period. MM-PBSA analysis of the last 10 ns of MD trajectories showed the stability of the complexes. From our results, we conclude that these drugs can also be useful for treating typhoid fever and can inhibit S. Typhi by interfering with the function of the DHFR enzyme. Communicated by Ramaswamy H. Sarma.

HEPATIC DYSFUNCTION IN MEDICAL INTENSIVE CAREUNIT PATIENTS PREDICTS POOR OUTCOME

BACKGROUND

A large number of patients admitted to the medical intensive care unit (MICU) have abnormal liver function tests (LFT). This includes patients with critical illness with or without preexisting liver disease and patients with acute primary liver injury. There are very few studies which have investigated the spectrum of liver disease, clinical profile and outcome in patients admitted to the MICU.

OBJECTIVE

To evaluate the occurrence, etiology, clinical profile, laboratory profile and outcome of hepatic dysfunction in patients admitted to the MICU. To evaluate the utility of model for end-stage liver disease (MELD) score on admission as a predictor of adverse short term outcome in patients with hepatic dysfunction admitted in MICU.

METHODS

It was a prospective observational study, conducted from December 2017 to December 2018 in a tertiary care hospital. Two hundred and two patients admitted to the MICU with LFTs as per the inclusion criteria were analyzed and their short-term outcome at 7 days was studied in relation to various parameters.

RESULTS

LFT abnormalities were present in 202/1126 (17.9%) of the patients admitted to MICU. Critical illness associated liver dysfunction was found in 172 (85.2%) patients, chronic liver disease in 11 (5.4%) patients and acute viral hepatitis in 19 (9.4%) patients. Most common symptom was fever (68.3%) followed by vomiting (48.0%). Among LFT abnormalities, elevated transaminases, raised international normalized ratio and high MELD score on admission correlated with poor short-term outcome. Requirement for inotropes and mechanical ventilation correlated with poor short-term outcome. Mortality did not differ significantly between patients with chronic liver disease, patients with acute viral hepatitis and patients with critical illness associated hepatic dysfunction. Hepatic dysfunction in MICU was associated with poor outcome and a high short-term mortality of 56.4% (114/202).

CONCLUSION

Liver function abnormality is common in patients who are admitted to the MICU and its presence is an indicator of poor short-term outcome.

Toward Typhoid Fever Elimination

Salmonella enterica serotype Typhi (S Typhi) causes typhoid fever and is responsible for an estimated 9 million cases and 110,000 deaths globally per annum. Typhoid fever is endemic in areas where water, sanitation, and hygiene (WaSH) infrastructure is poor. Serious complications develop in approximately 10%-15% of patients if left untreated, and this is driven by inadequate diagnostic methods and the high burden of antibiotic-resistant strains, complicating clinical management and ultimately prognosis. Asymptomatic chronic carriers, in addition to acutely infected patients, contribute to continued transmission through the shedding of the organism in the feces. The high morbidity and mortality of typhoid fever in low- and middle-income countries reinforce the need for an integrated control approach, which may ultimately lead to elimination of the disease in the 21^st century. Here we discuss the challenges faced in pursuit of typhoid fever elimination.

Typhoid fever presenting with gastric ulcer bleeding

Background

Enteric fever is a systemic disease caused by Salmonella enterica serovar Typhi or Salmonella enterica serovar Paratyphi, characterized by high fever and abdominal pain. Most patients with enteric fever improve within a few days after antibiotic treatment. However, some patients do not recover as easily and develop fatal life-threatening complications, including intestinal hemorrhage. Lower gastrointestinal bleeding has been reported in 10% of cases. However, upper gastrointestinal bleeding has rarely been reported in patients with enteric fever. We present a case of gastric ulcer hemorrhage caused by enteric fever.

Case presentation

A 32-year-old woman, complaining of fever lasting four days and right upper quadrant pain and melena that started one day before admission, consulted our hospital. Abdominal computed tomography revealed mild hepatomegaly and gastroscopy revealed multiple active gastric ulcers with flat black hemorrhagic spots. The melena of the patient stopped on the third day. On the fifth admission day, she developed hematochezia. At that time, Salmonella enterica serovar Typhi was isolated from the blood culture. The antibiotic regimen was switched to ceftriaxone. Her hematochezia spontaneously resolved the following day. Finally, the patient was discharged on the 12th admission day without clinical symptoms. However, her fever recurred one month after discharge, and she was readmitted and Salmonella enterica serovar Typhi was confirmed again via blood culture. She was treated with ceftriaxone for one month, and was discharged without complications.

Conclusion

Our case showed that although rare, active gastric ulcers can develop in patients with enteric fever. Therefore, upper and lower gastrointestinal bleeding should be suspected in patients with enteric fever, especially showing relapsing bacteremia.

Bacterial infection disrupts established germinal center reactions through monocyte recruitment and impaired metabolic adaptation

Consecutive exposures to different pathogens are highly prevalent and often alter the host immune response. However, it remains unknown how a secondary bacterial infection affects an ongoing adaptive immune response elicited against primary invading pathogens. We demonstrated that recruitment of Sca-1+ monocytes into lymphoid organs during Salmonella Typhimurium (STm) infection disrupted pre-existing germinal center (GC) reactions. GC responses induced by influenza, plasmodium, or commensals deteriorated following STm infection. GC disruption was independent of the direct bacterial interactions with B cells and instead was induced through recruitment of CCR2-dependent Sca-1+ monocytes into the lymphoid organs. GC collapse was associated with impaired cellular respiration and was dependent on TNFα and IFNγ, the latter of which was essential for Sca-1+ monocyte differentiation. Monocyte recruitment and GC disruption also occurred during LPS-supplemented vaccination and Listeria monocytogenes infection. Thus, systemic activation of the innate immune response upon severe bacterial infection is induced at the expense of antibody-mediated immunity.

Whole genome sequence analysis of Salmonella Typhi in Papua New Guinea reveals an established population of genotype 2.1.7 sensitive to antimicrobials

BACKGROUND

Typhoid fever, a systemic infection caused by Salmonella enterica serovar Typhi, remains a considerable public health threat in impoverished regions within many low- and middle-income settings. However, we still lack a detailed understanding of the emergence, population structure, molecular mechanisms of antimicrobial resistance (AMR), and transmission dynamics of S. Typhi across many settings, particularly throughout the Asia-Pacific islands. Here we present a comprehensive whole genome sequence (WGS) based overview of S. Typhi populations circulating in Papua New Guinea (PNG) over 30 years.

PRINCIPLE FINDINGS

Bioinformatic analysis of 86 S. Typhi isolates collected between 1980-2010 demonstrated that the population structure of PNG is dominated by a single genotype (2.1.7) that appears to have emerged in the Indonesian archipelago in the mid-twentieth century with minimal evidence of inter-country transmission. Genotypic and phenotypic data demonstrated that the PNG S. Typhi population appears to be susceptible to former first line drugs for treating typhoid fever (chloramphenicol, ampicillin and co-trimoxazole), as well as fluoroquinolones, third generation cephalosporins, and macrolides. PNG genotype 2.1.7 was genetically conserved, with very few deletions, and no evidence of plasmid or prophage acquisition. Genetic variation among this population was attributed to either single point mutations, or homologous recombination adjacent to repetitive ribosomal RNA operons.

SIGNIFICANCE

Antimicrobials remain an effective option for the treatment of typhoid fever in PNG, along with other intervention strategies including improvements to water, sanitation and hygiene (WaSH) related infrastructure and potentially the introduction of Vi-conjugate vaccines. However, continued genomic surveillance is warranted to monitor for the emergence of AMR within local populations, or the introduction of AMR associated genotypes of S. Typhi in this setting.

The Burden of Typhoid Fever in Sub-Saharan Africa: A Perspective

While typhoid fever has largely been eliminated in high-income regions which have developed modern water, sanitation, and hygiene facilities, it remains a significant public health burden resulting in morbidity and mortality among millions of individuals in resource-constrained settings. Prevention and control efforts are needed that integrate several high-impact interventions targeting facilities and infrastructure, including those addressing improvements in sanitation, access to safe water, and planned urbanization, together with parallel efforts directed at effective strategies for use of typhoid conjugate vaccines (TCV). The use of TCVs is a critical tool with the potential of having a rapid impact on typhoid fever disease burden; their introduction will also serve as an important strategy to combat evolving antimicrobial resistance to currently available typhoid fever treatments. Well-designed epidemiological surveillance studies play a critical role in establishing the need for, and monitoring the impact of, typhoid fever control and prevention strategies implemented by public health authorities. Here, we present a perspective based on a narrative review of the impact of typhoid fever on morbidity and mortality in sub-Saharan Africa and discuss ongoing surveillance activities and the role of vaccination in prevention and control efforts.

Cooperative defenses during enteropathogenic infection

During their co-evolution with pathogens, hosts acquired defensive health strategies that allow them to maintain their health or promote recovery when challenged with infections. The cooperative defense system is a largely unexplored branch of these evolved defense strategies. Cooperative defenses limit physiological damage and promote health without having a negative impact on a pathogen's ability to survive and replicate within the host. Here, we review recent discoveries in the new field of cooperative defenses using the model pathogens Citrobacter rodentium and Salmonella enterica. We discuss not only host-encoded but also pathogen-encoded mechanisms of cooperative defenses. Cooperative defenses remain an untapped resource in clinical medicine. With a global pandemic exacerbated by a lack of vaccine access and a worldwide rise in antibiotic resistance, the study of cooperative defenses offers an opportunity to safeguard health in the face of pathogenic infection.

Salmonellosis Including Enteric Fever

Salmonella is a gram-negative, motile, nonsporulating, facultative anaerobic bacillus, belongs to the family Enterobacteriaceae. The bacteria were first identified in 1884. It is transmitted through direct contact with an infected person or indirect contact by the consumption of contaminated food and water. More than 2500 serotypes of Salmonella enterica have been identified but less than 100 serotypes are known to cause infections in humans. S. enterica serovar typhi (S. typhi) and S. enterica serovar paratyphi (S. paratyphi A B C) cause enteric fever, whereas nontyphoidal Salmonella serotypes (NTS) cause diarrhea. NTS commonly presents with gastroenteritis and is a self-limiting disease. Enteric fever is a potentially life-threatening acute febrile systemic infection and is diagnosed by isolating a pathogen on culture. With the emergence of the extensive drug-resistant (XDR) S. typhi clone, limited treatment options are available. Vaccination of persons at risk, improvement of sanitation, promotion of food hygiene, and detection and control of chronic carriers are essential preventive control measures of enteric fever.

An observational study to compare the diagnostic accuracy of rapid antigen test and rapid antibody tests in various periods of enteric fever

A cross-sectional observational study was done on 180 fever patients to assess the diagnostic accuracy of rapid serological tests in early detection (<5 days of fever) of S. typhi and S. paratyphi in comparison to blood culture and Widal test Blood culture was positive in 58 (32.22%) cases. The diagnostic accuracy (<5 days of fever) of rapid antigen test, rapid antibody test, and Widal test was 45.56%, 42.22%, and 41.11% (p = 0.675) while sensitivity was 68.97%, 48.28%, and 46.55%, respectively. In conclusion, rapid antigen test holds moderately higher sensitivity in the first five days of fever as compared to rapid antibody and Widal tests. It is recommended that the antigen detection tests should be used for screening enteric fever in the first week of presentation.