Invasive Nontyphoidal Salmonella Disease in Africa

Non-typhoidal Salmonella transmission reservoirs in Sub-Saharan Africa: a genomic assessment from a one health perspective

BACKGROUND

In sub-Saharan Africa, invasive non-typhoidal Salmonella disease, characterized by bloodstream infections with high mortality rates, poses a significant public health burden. In Africa, Salmonella enterica, which are typically livestock- associated pathogens in industrialised countries, have genetically evolved and anthroponotic transmission has been proposed for S. Typhimurium ST313. In this study, we investigated the hypothesis of an exclusively anthroponotic transmission reservoir of Salmonella enterica ST313 and aimed to identify reservoirs for other Salmonella spp., shedding light on their occurrence in different ecological niches.

METHODS

This study used a One Health approach and Salmonella were isolated from humans, livestock and the environment, in Tanzania and in Ghana. Salmonella spp. were identified by biochemical methods and antibiotic susceptibility was tested. Isolates were subjected to whole genome sequencing.

RESULTS

Out of 9,086 collected samples, 222 Salmonella enterica were identified comprising 58 serovars. The highest level of antimicrobial resistance was found in humans with emerging fluroquinolone resistance and multidrug resistance being highest in isolates from blood cultures (24%, n/N = 11/46). For the invasive strains, the sequence types S. Typhimurium ST313 and ST19 were most common and ST313 was associated with multidrug resistance, followed by S. Enteritidis ST11 and ST147 and S. Dublin ST10. An overlap of sequence types amongst human-livestock and human-environmental strains was detected for S. Typhimurium ST19 but not found for ST313 and the two serovars Dublin and Enteritidis.

CONCLUSIONS

Our study adds further evidence of S. Typhimurium ST313 being restricted to a human reservoir and linked to multidrug resistance. Additionally, our study provides comprehensive insights into Salmonella genetic diversity and distribution among humans, animals and the environment in Ghana and in Tanzania. This sheds light on other potential reservoirs for infections, all of which show antimicrobial resistance. Further research into stool carriage is warranted, encompassing patients with invasive disease and those with and without diarrhoea, to identify transmission reservoirs in particular for invasive disease-causing strains. These findings underscore the need for integrated One Health approaches to effectively monitor and manage salmonellosis and mitigate public health risks. Continued research into the spread of Salmonella spp. and its evolution is crucial for targeted interventions and disease control.

Landscape analysis of invasive non-typhoidal salmonella (iNTS) disease and iNTS vaccine use case and demand: Report of a WHO expert consultation

Invasive disease caused by non-typhoidal Salmonella serovars (iNTS) occurs with increased risk in the presence of other comorbidities such as malaria, HIV, malnutrition, anaemia and sickle cell disease. While infection with non-typhoidal (NTS) serovars often results in self-limited enterocolitis in high-income settings, in sub-Saharan Africa (SSA) where these risk-comorbidities are common, an invasive (iNTS) disease phenotype is seen, associated with up to 20 % case-fatality ratio, and antimicrobial resistance is both significant and growing. The need to evaluate the potential public health value of vaccines against iNTS disease is increasingly being recognized, and several candidate vaccines are in early development. A better understanding of the global burden and epidemiology of iNTS disease, as well as the potential public health and socio-economic benefits that iNTS vaccines may offer is fundamental to support and justify the investments in vaccine development. In addition, the pathways for licensure, policy recommendations and eventual vaccine prioritization and use in low- and middle-income countries (LMICs) need to be defined. Here, we report on the proceedings of an expert consultation held on 29 November - 1 December 2021 as part of an overall project to develop a Full Value of Vaccines Assessment (FVVA) for iNTS vaccines and in addition to more recent iNTS vaccine developments. Experts at the consultation reviewed the current evidence on iNTS disease and discussed knowledge gaps to be addressed to accelerate vaccine development, licensure and introduction, as well as LMIC perspectives on potential iNTS vaccine use and demand. The learnings from this consultation are critical inputs to inform remaining work under the iNTS FVVA project.

The global, regional, and national burden of Invasive Non-typhoidal Salmonella (iNTS): An analysis from the Global Burden of Disease Study 1990-2021

OBJECTIVES

Invasive Non-typhoidal Salmonella (iNTS) can cause serious, life-threatening, and invasive infections, posing great challenges to public health. We aimed to systematically review the burden of iNTS disease based on Global Burden of Diseases (GBD) 2021.

METHODS

We extracted data for the incidence, death, and disability-adjusted life-years (DALYs) associated with iNTS from GBD 2021, providing an overview of its epidemiology while examining trends from 1990 to 2021. Additionally, we decomposed changes of iNTS-related burden, and quantified cross-country inequalities.

RESULTS

GBD 2021 estimated 509976(95%UI,413361 to 606167) incident cases of iNTS worldwide in 2021, with the most cases and highest age-standardized rate (ASR) in Western Sub-Saharan Africa. The low SDI region had the most cases of iNTS in 2021. The incidence and DALYs rates were highest in the Low SDI region. Among all age groups, the incidence, death, and DALYs rate of iNTS were primarily concentrated among the following age groups: <1 year, 1-4 years, 5-9 years, 10-14 years, and 15-19 years. The highest rates were observed in the <1-year group. The results of joinpoint regression analysis revealed that the global burden of iNTS increased overall from 1990 to 2005, followed by notable decrease from 2005 to 2021 at varying rates. Decomposition analysis found that population growth (103.93%) and epidemiological change (48.34%) were responsible for motivating the changes in iNTS global burden. Cross-country inequality analysis revealed that the SDI-related inequalities were moderated from 1990 to 2021.

CONCLUSIONS

The global burden of iNTS is still high, and the distribution patterns vary across different countries and territories. The global burden of iNTS was primarily noteworthy among children and adolescents, with the highest burden among infants. The changes in the iNTS burden were primarily driven by population growth and epidemic transition. Despite varying iNTS burdens across different SDI regions, SDI-related inequalities across countries became moderated gradually over time. This study reported the global disease burden and temporal trends of iNTS disease, and underscores the need for age- and region-specific strategies to mitigate the corresponding global burden.

Developing a clinical prediction model to modify empirical antibiotics for non-typhoidal Salmonella bloodstream infection in children under-five in the Democratic Republic of Congo

BACKGROUND

Non-typhoidal Salmonella (NTS) frequently cause bloodstream infection in children under-five in sub-Saharan Africa, particularly in malaria-endemic areas. Due to increasing drug resistance, NTS are often not covered by standard-of-care empirical antibiotics for severe febrile illness. We developed a clinical prediction model to orient the choice of empirical antibiotics (standard-of-care versus alternative antibiotics) for children admitted to hospital in settings with high proportions of drug-resistant NTS.

METHODS

Data were collected during a prospective cohort study in children (> 28 days-< 5 years) admitted with severe febrile illness to Kisantu district hospital, DR Congo. The outcome variable was blood culture confirmed NTS bloodstream infection; the comparison group were children without NTS bloodstream infection. Predictors were selected a priori based on systematic literature review. The prediction model was developed with multivariable logistic regression; a simplified scoring system was derived. Internal validation to estimate optimism-corrected performance was performed using bootstrapping and net benefits were calculated to evaluate clinical usefulness.

RESULTS

NTS bloodstream infection was diagnosed in 12.7% (295/2327) of enrolled children. The area under the curve was 0.79 (95%CI: 0.76-0.82) for the prediction model, and 0.78 (0.85-0.80) for the scoring system. The estimated calibration slopes were 0.95 (model) and 0.91 (scoring system). At a decision threshold of 20% NTS risk, the prediction model and scoring system had 57% and 53% sensitivity, and 85% specificity. The net benefit for decisions thresholds < 30% ranged from 2.4 to 3.9 per 100 children.

CONCLUSION

The model predicts NTS bloodstream infection and can support the choice of empiric antibiotics to include coverage of drug-resistant NTS, in particular for decision thresholds < 30%. External validation studies are needed to investigate generalizability.

TRIAL REGISTRATION

DeNTS study, clinicaltrials.gov: NCT04473768 (registration 16/07/2020) and TreNTS study, clinicaltrials.gov: NCT04850677 (registration 20/04/2021).

Foodborne Infections and Salmonella: Current Primary Prevention Tools and Future Perspectives

Salmonella is considered the major zoonotic and foodborne pathogen responsible for human infections. It includes the serovars causing typhoid fever (S. typhi and S. paratyphi) and the non-typhoidal salmonella (NTS) serovars (S. enteritidis and S. typhimurium), causing enteric infections known as "Salmonellosis". NTS represents a major public health burden worldwide. The consumption of S. enteritidis-contaminated animal foods is the main source of this disease in humans, and eradicating bacteria from animals remains a challenge. NTS causes various clinical manifestations, depending on the quantity of bacteria present in the food and the immune status of the infected individual, ranging from localized, self-limiting gastroenteritis to more serious systemic infections. Salmonellosis prevention is based on hygienic and behavioral rules related to food handling that aim to reduce the risk of infection. However, no vaccine against NTS is available for human use. This aspect, in addition to the increase in multidrug-resistant strains and the high morbidity, mortality, and socioeconomic costs of NTS-related diseases, makes the development of new prevention and control strategies urgently needed. The success of the vaccines used to protect against S. typhi encouraged the development of NTS vaccine candidates, including live attenuated, subunit-based, and recombinant-protein-based vaccines. In this review, we discuss the epidemiological burden of Salmonellosis and its primary prevention, focusing on the current status and future perspectives of the vaccines against NTS.

Neutrophil prime unique transcriptional responses in intestinal organoids during infection with nontyphoidal Salmonella enterica serovars

Nontyphoidal strains of Salmonella enterica are a major cause of foodborne illnesses, and infection with these bacteria results in inflammatory gastroenteritis. Polymorphonuclear leukocytes (PMNs), also known as neutrophils, are a dominant immune cell type found at the site of infection in Salmonella-infected individuals, but how they regulate infection outcome is not well understood. Here, we used a co-culture model of primary human PMNs and human intestinal organoids to probe the role of PMNs during infection with two of the most prevalent Salmonella serovars: Salmonella enterica serovar Enteritidis and Typhimurium. Using a transcriptomics approach, we identified a dominant role for PMNs in mounting differential immune responses including production of pro-inflammatory cytokines, chemokines, and antimicrobial peptides. We also identified specific gene sets that were induced by PMNs in response to Enteritidis or Typhimurium infection. By comparing host responses to these serovars, we uncovered differential regulation of host metabolic pathways particularly induction of cholesterol biosynthetic pathways during Typhimurium infection and suppression of RNA metabolism during Enteritidis infection. Together, these findings provide insight into the role of human PMNs in modulating different host responses to pathogens that cause similar disease in humans.IMPORTANCENontyphoidal serovars of Salmonella enterica are known to induce robust recruitment of polymorphonuclear leukocytes (PMNs) in the gut during early stages of infection, but the specific role of PMNs in regulating infection outcome of different serovars is poorly understood. Due to differences in human infection progression compared to small animal models, characterizing the role of PMNs during infection has been challenging. Here, we used a co-culture model of human intestinal organoids with human primary PMNs to study the role of PMNs during infection of human intestinal epithelium. Using a transcriptomics approach, we define PMN-dependent reprogramming of the host response to Salmonella, establishing a clear role in amplifying pro-inflammatory gene expression. Additionally, the host response driven by PMNs differed between two similar nontyphoidal Salmonella serovars. These findings highlight the importance of building more physiological infection models to replicate human infection conditions to study host responses specific to individual pathogens.

Platelet aggregation responses to Salmonella Typhimurium are determined by host anti-Salmonella antibody levels

Invasive non-typhoidal Salmonella infections are responsible for >75 000 deaths/year and >500 000 cases/year globally. Seventy-five percent of these cases occur in Sub-Saharan Africa, an increasing number of which are from multi-drug resistant strains. Interactions between bacteria and platelets can lead to thrombus formation, which can be beneficial for control of infection (immunothrombosis), or harmful through uncontrolled inflammation and organ damage (thromboinflammation). It is unknown whether Salmonella Typhimurium can activate human platelets. To assess this, light transmission aggregometry was used to measure platelet activation by two different Salmonella Typhimurium strains in 26 healthy donors in platelet-rich plasma and washed platelets. In platelet-rich plasma, but not in washed platelets, Salmonella Typhimurium activated platelets in a donor- and strain-dependent manner mediated through the low affinity immune receptor FcγRIIA and the feedback agonists, ADP and thromboxane A2. Plasma swap studies between strong and weak responders demonstrated a plasma component was responsible for the variation between donors. Depletion of anti-Salmonella antibodies from plasma abolished Salmonella-induced platelet aggregation responses, and addition of polyclonal anti-Salmonella antibody allowed aggregation in washed platelets. Correlating levels of anti-Salmonella total IgG or the IgG1, IgG2, IgG3 and IgG4 subclasses to platelet responses revealed total IgG levels, rather than levels of individual subclasses, positively correlated with maximum platelet aggregation results, and negatively with lag times. Overall, we show that anti-Salmonella IgG antibodies are responsible for donor variation in platelet aggregation responses to Salmonella and mediate this activity through FcγRIIA.

Fighting the enemy within: Systemic immune defense against mucosal Salmonella infection

Salmonella infection remains a persistent global health threat, as different serovars induce a range of clinical disease, depending upon bacterial virulence and host susceptibility. While some Salmonella serovars induce gastroenteritis in healthy individuals, others can cause more serious systemic enteric fever or invasive nontyphoidal Salmonellosis. The rise of antibiotic resistance, coupled with the absence of effective vaccines for most serovars, perpetuates the spread of Salmonella in endemic regions. A detailed mechanistic understanding of immunity to Salmonella infections has been aided by the availability of mouse models that have served as a valuable tool for understanding host-pathogen interactions under controlled laboratory conditions. These mouse studies have delineated the processes by which early inflammation is triggered after infection, how adaptive immunity is initiated in lymphoid tissues, and the contribution of lymphocyte memory responses to resistance. While recent progress has been made in vaccine development for some causes of enteric fever, deeper understanding of Salmonella-specific immune memory might allow the formation of new vaccines for all serovars. This review will provide a summary of our understanding of vaccination and protective immunity to Salmonella with a focus on recent developments in T cell memory formation.

Shedding of nontyphoidal Salmonella by asymptomatic convalescing children under 5 years as a risk factor for invasive disease in Mukuru informal settlement in Nairobi, Kenya

Nontyphoidal Salmonella (NTS) is a predominant cause of invasive disease in sub-Saharan Africa especially among children under 5 years. Asymptomatic fecal shedding of NTS is hypothesized to contribute to the human-to-human transmission of NTS especially in low-resource settings. However, the role of pathogen shedding in invasive disease is unknown. This study aimed to investigate the prevalence and duration of fecal shedding of NTS among children under 5 years convalescing from invasive NTS disease and among healthy individuals in the community. Children presenting with fever of ≥38°C with or without diarrhea were recruited at four health facilities in Nairobi, between June 2021 and August 2023. Blood and stool samples collected were subjected to culture for the isolation of NTS (S. Enteritidis and S. Typhimurium). Children with NTS culture-positive samples (index cases) were followed up post-acute disease where household contacts and controls provided stool samples for isolation of NTS. NTS prevalence among the 3,293 individuals recruited was 1.52%. Asymptomatic shedding post-treatment was observed in almost one-third (31%) of the 42 index cases followed up. Of the 13 with intestinal shedding, 7 were shedding NTS of the same sequence type (ST) as the one recovered during acute disease. The longest duration of intestinal shedding was 3 months post-treatment. Of the 241 healthy individuals recruited, 8 had asymptomatic shedding of NTS, and 2 of these were closely related to those recovered from index cases. These findings support the hypothesis of human-to-human transmission of NTS in sub-Saharan Africa highlighting the possible benefit of vaccine introduction.

IMPORTANCE

Asymptomatic fecal shedding of nontyphoidal Salmonella (NTS) is hypothesized to contribute to the human-to-human transmission of NTS especially in low-resource settings which could lead to invasive disease among high-risk populations, especially children. Our findings reiterate the hypothesis that human reservoirs could be important in the transmission of nontyphoidal Salmonella in sub-Saharan Africa. This underscores the importance of developing infection prevention measures which could include vaccine deployment and improving water, sanitation and hygiene infrastructure.

Nontyphoidal Salmonella Hepatitis: A Rare Complication of a Common Enteric Infection

Hepatitis from nontyphoidal Salmonella gastroenteritis is rare, especially in immunocompetent patients. We present the case of a 30-year-old woman who was found to have Salmonella serotype C2 gastroenteritis and elevated liver function tests concerning for concurrent hepatitis. An extensive workup was negative for other etiologies, making Salmonella the likely culprit. The patient was managed with supportive measures as her liver function tests and symptoms were improving before obtaining microbiological data. Since the role of antibiotic therapy in such cases is not well studied, disease severity in accordance with current guidelines should be used to tailor treatment on a case-by-case basis.

Salmonella Bacteremia in Spanish Pediatric Emergency Departments: Uncommon But Not Mild

BACKGROUND

Salmonella spp. is an uncommon microorganism in bloodstream infections among pediatric patients in our setting, although in developing countries it is the most common causative organism in blood cultures.

METHODS

We describe the children presenting to pediatric emergency departments and diagnosed with Salmonella bacteremia (SB) and identify clinical and laboratory predictors of poor outcome (ie, complications, sequelae and death) by bivariate analysis. We performed an observational study and subanalysis of a multicenter prospective registry, including patients <18 years of age with a positive blood culture obtained at any of the 22 participating Spanish pediatric emergency departments between 2011 and 2016. We considered young age, chronic diseases, immunosuppressive treatment and intestinal flora disruption as risk factors for SB.

RESULTS

Of the 55 patients with SB (3.2% of registered bacteremia), 32 (58.2%) had no risk factors for SB, 42 (76.3%) had a normal pediatric assessment triangle and 45 (81.8%) an associated gastrointestinal infection (acute gastroenteritis or enteric fever). Nine (16.4%) had a poor outcome, including 1 death (1.8%). A poor outcome was more common in patients with an abnormal pediatric assessment triangle [odds ratio (OR): 51.6; 95% confidence interval (CI): 9.2-289.5], an altered physical examination (OR: 15.2; 95% CI: 4.4-58.8) and elevated C-reactive protein (OR: 1.01; 95% CI: 1.005-1.03).

CONCLUSIONS

Most SBs were related to a gastrointestinal infection. One in 6 children had a poor outcome; abnormal pediatric assessment triangle on arrival (25% of patients) was the main risk factor identified.

Bacteraemia in Tropical Australia: A Review

Purpose of Review

This review discusses the trends of bacteraemia and their outcomes in tropical regions of Australia. Bacteraemia can frequently lead to severe sepsis and potentially life-threatening consequences. Epidemiology of bacteraemia is ever evolving.

Recent Findings

This review outlines the current patterns of bacteraemia in tropical regions of Australia, focusing on their outcomes and associated risk factors. The most frequently reported causes of bacteraemia were Staphylococcus aureus and Escherichia coli. There has been an increase in published incidence of Group A Streptococcus, methicillin-resistant Staphylococcus aureus and Burkholderia pseudomallei bacteraemia cases, while Streptococcus pneumoniae bacteraemia exhibited a declining trend. Factors specific to tropical environments and the higher representation of Indigenous populations in these areas were identified as contributing to the elevated incidence rates.

Summary

Bacteraemia was found to be an increasing healthcare burden to the Australian tropical regions. Ideally, linkage of existing data from healthcare settings could be utilised to obtain more accurate, comprehensive and up to date information of trends and patterns of bacteraemia.

Vaccine value profile for invasive non-typhoidal Salmonella disease

Invasive non-typhoidal Salmonella (iNTS) disease is an under-recognized high-burden disease causing major health and socioeconomic issues in sub-Saharan Africa (sSA), predominantly among immune-naïve infants and young children, including those with recognized comorbidities such as HIV infection. iNTS disease is primarily caused by Salmonella enterica serovar Typhimurium sequence type (ST) 313 and 'African-restricted clades' of Salmonella Enteritidis ST11 that have emerged across the African continent as a series of epidemics associated with acquisition of new antimicrobial resistance. Due to genotypes with a high prevalence of antimicrobial resistance and scarcity of therapeutic options, these NTS serovars are designated by the World Health Organization as a priority pathogen for research and development of interventions, including vaccines, to address and reduce NTS associated bacteremia and meningitis in sSA. Novel and traditional vaccine technologies are being applied to develop vaccines against iNTS disease, and the results of the first clinical trials in the infant target population should become available in the near future. The "Vaccine Value Profile" (VVP) addresses information related predominantly to invasive disease caused by Salmonella Enteritidis and Salmonella Typhimurium prevalent in sSA. Information is included on stand-alone iNTS disease candidate vaccines and candidate vaccines targeting iNTS disease combined with another invasive serotype, Salmonella Typhi, that is also common across sSA. Out of scope for the first version of this VVP is a wider discussion on either diarrheagenic NTS disease (dNTS) also associated with Salmonella Enteritidis and Salmonella Typhimurium or the development of a multivalent Salmonella vaccines targeting key serovars for use globally. This VVP for vaccines to prevent iNTS disease is intended to provide a high-level, holistic assessment of the information and data that are currently available to inform the potential public health, economic, and societal value of pipeline vaccines and vaccine-like products. Future versions of this VVP will be updated to reflect ongoing activities such as vaccine development strategies and a "Full Vaccine Value Assessment" that will inform the value proposition of an iNTS disease vaccine. This VVP was developed by a working group of subject matter experts from academia, non-profit organizations, public private partnerships, and multi-lateral organizations, and in collaboration with stakeholders from the World Health Organization African Region. All contributors have extensive expertise on various elements of the iNTS disease VVP and collectively aimed to identify current research and knowledge gaps. The VVP was developed using only existing and publicly available information.

The Economic Burden of Non-Typhoidal Salmonella and Invasive Non-Typhoidal Salmonella Infection: A Systematic Literature Review

Non-typhoidal Salmonella (NTS) infection and invasive non-typhoidal Salmonella (iNTS) infection cause a significant global health and economic burden. This systematic review aims to investigate the reported economic burden of NTS and iNTS infection, identify research gaps, and suggest future research directions. Data from PubMed and Embase databases up to April 2022 were reviewed, and articles were screened based on predefined criteria. Cost data were extracted, categorized into direct medical costs (DMCs), direct non-medical costs (DNMCs), and indirect costs (ICs), and converted into US dollars (year 2022). Data primarily originated from high-income countries (37 out of 38), with limited representation from Africa and resource-limited settings. For inpatients, DMCs were the primary cost driver for both NTS and iNTS illnesses, with estimates ranging from USD 545.9 (Taiwan, a region of China) to USD 21,179.8 (Türkiye) for NTS and from USD 1973.1 (Taiwan, a region of China) to USD 32,507.5 (United States of America) for iNTS per case. DNMCs and ICs varied widely across studies. Although study quality improved over time, methodological differences persisted. This review underscores the lack of economic data on NTS and iNTS in resource-limited settings. It also highlights the need for economic burden data in resource-limited settings and a standardized approach to generate global datasets, which is critical for informing policy decisions, especially regarding future vaccines.

Lipopolysaccharide with long O-antigen is crucial for Salmonella Enteritidis to evade complement activity and to facilitate bacterial survival in vivo in the Galleria mellonella infection model

Bacterial resistance to serum is a key virulence factor for the development of systemic infections. The amount of lipopolysaccharide (LPS) and the O-antigen chain length distribution on the outer membrane, predispose Salmonella to escape complement-mediated killing. In Salmonella enterica serovar Enteritidis (S. Enteritidis) a modal distribution of the LPS O-antigen length can be observed. It is characterized by the presence of distinct fractions: low molecular weight LPS, long LPS and very long LPS. In the present work, we investigated the effect of the O-antigen modal length composition of LPS molecules on the surface of S. Enteritidis cells on its ability to evade host complement responses. Therefore, we examined systematically, by using specific deletion mutants, roles of different O-antigen fractions in complement evasion. We developed a method to analyze the average LPS lengths and investigated the interaction of the bacteria and isolated LPS molecules with complement components. Additionally, we assessed the aspect of LPS O-antigen chain length distribution in S. Enteritidis virulence in vivo in the Galleria mellonella infection model. The obtained results of the measurements of the average LPS length confirmed that the method is suitable for measuring the average LPS length in bacterial cells as well as isolated LPS molecules and allows the comparison between strains. In contrast to earlier studies we have used much more precise methodology to assess the LPS molecules average length and modal distribution, also conducted more subtle analysis of complement system activation by lipopolysaccharides of various molecular mass. Data obtained in the complement activation assays clearly demonstrated that S. Enteritidis bacteria require LPS with long O-antigen to resist the complement system and to survive in the G. mellonella infection model.

Salmonella enterica serovar Typhimurium ST313 sublineage 2.2 has emerged in Malawi with a characteristic gene expression signature and a fitness advantage

Invasive non-typhoidal Salmonella (iNTS) disease is a serious bloodstream infection that targets immune-compromised individuals, and causes significant mortality in sub-Saharan Africa. Salmonella enterica serovar Typhimurium ST313 causes the majority of iNTS in Malawi. We performed an intensive comparative genomic analysis of 608 S. Typhimurium ST313 isolates dating between 1996 and 2018 from Blantyre, Malawi. We discovered that following the arrival of the well-characterized S. Typhimurium ST313 lineage 2 in 1999, two multidrug-resistant variants emerged in Malawi in 2006 and 2008, designated sublineages 2.2 and 2.3, respectively. The majority of S. Typhimurium isolates from human bloodstream infections in Malawi now belong to sublineages 2.2 or 2.3. To understand the emergence of the prevalent ST313 sublineage 2.2, we studied two representative strains, D23580 (lineage 2) and D37712 (sublineage 2.2). The chromosome of ST313 lineage 2 and sublineage 2.2 only differed by 29 SNPs/small indels and a 3 kb deletion of a Gifsy-2 prophage region including the sseI pseudogene. Lineage 2 and sublineage 2.2 had distinctive plasmid profiles. The transcriptome was investigated in 15 infection-relevant in vitro conditions and within macrophages. During growth in physiological conditions that do not usually trigger S. Typhimurium SPI2 gene expression, the SPI2 genes of D37712 were transcriptionally active. We identified down-regulation of flagellar genes in D37712 compared with D23580. Following phenotypic confirmation of transcriptomic differences, we discovered that sublineage 2.2 had increased fitness compared with lineage 2 during mixed growth in minimal media. We speculate that this competitive advantage is contributing to the emergence of sublineage 2.2 in Malawi.

Meningitis and Bacteremia by Unusual Serotype of Salmonella enterica Strain: A Whole Genome Analysis

Background

Although meningitis caused by Salmonella species is relatively rare and accounts for <1% of the confirmed cases in neonates, it is associated with case complications and fatality rates up to 50-70% when compared to other forms of Gram-negative bacilli meningitis.

Objectives

We conducted an investigation into the first reported case of neonatal meningitis caused by nontyphoidal S. enterica in Jazan, a region in the southwestern part of Saudi Arabia.

Methods

CSF and blood culture were collected from a female neonate patient to confirm the presence of bacterial meningitis. WGS was conducted to find out the comprehensive genomic characterization of S. enterica isolate.

Results

A 3-week-old infant was admitted to a local hospital with fever, poor feeding, and hypoactivity. She was diagnosed with Salmonella meningitis and bacteremia caused by S. enterica, which was sensitive to all antimicrobials tested. WGS revealed the specific strain to be S. enterica serotype Johannesburg JZ01, belonging to ST515 and cgMLST 304742.

Conclusions

We presented a genomic report of rare case of NTS meningitis in an infant who is living in a rural town in Jazan region, Saudi Arabia. Further research is required to understand the impact of host genetic factors on invasive nontyphoidal Salmonella infection.

Examining geospatial and temporal distribution of invasive non-typhoidal Salmonella disease occurrence in sub-Saharan Africa: a systematic review and modelling study

BACKGROUND

Invasive non-typhoidal Salmonella (iNTS) disease is a significant health concern in sub-Saharan Africa. While our knowledge of a larger-scale variation is growing, understanding of the subnational variation in iNTS disease occurrence is lacking, yet crucial for targeted intervention.

METHOD

We performed a systematic review of reported occurrences of iNTS disease in sub-Saharan Africa, consulting literature from PubMed, Embase and Web of Science published since 2000. Eligibility for inclusion was not limited by study type but required that studies reported original data on human iNTS diseases based on the culture of a normally sterile site, specifying subnational locations and the year, and were available as full-text articles. We excluded studies that diagnosed iNTS disease based on clinical indications, cultures from non-sterile sites or serological testing. We estimated the probability of occurrence of iNTS disease for sub-Saharan Africa on 20 km × 20 km grids by exploring the association with geospatial covariates such as malaria, HIV, childhood growth failure, access to improved water, and sanitation using a boosted regression tree.

RESULTS

We identified 130 unique references reporting human iNTS disease in 21 countries published from 2000 through 2020. The estimated probability of iNTS occurrence grids showed significant spatial heterogeneity at all levels (20 km × 20 km grids, subnational, country and subregional levels) and temporal heterogeneity by year. For 2020, the probability of occurrence was higher in Middle Africa (0.34, 95% CI: 0.25 to 0.46), followed by Western Africa (0.33, 95% CI: 0.23 to 0.44), Eastern Africa (0.24, 95% CI: 0.17 to 0.33) and Southern Africa (0.08, 95% CI: 0.03 to 0.11). Temporal heterogeneity indicated that the probability of occurrence increased between 2000 and 2020 in countries such as the Republic of the Congo (0.05 to 0.59) and Democratic Republic of the Congo (0.10 to 0.48) whereas it decreased in countries such as Uganda (0.65 to 0.23) or Zimbabwe (0.61 to 0.37).

CONCLUSION

The iNTS disease occurrence varied greatly across sub-Saharan Africa, with certain regions being disproportionately affected. Exploring regions at high risk for iNTS disease, despite the limitations in our data, may inform focused resource allocation. This targeted approach may enhance efforts to combat iNTS disease in more affected areas.

A Population-Based Study on the Incidence, Risk Factors, and Outcome of Salmonella Bloodstream Infections in South Sweden 2012-2022

INTRODUCTION

Invasive infections caused by Salmonella are a significant global health concern. This population-based study aimed to comprehensively analyze invasive Salmonella infections in South Sweden, focusing on incidence, clinical presentation, risk factors, and outcomes.

METHODS

This population-based observational cohort study, conducted from 2012 to 2022, included all patients with Salmonella bloodstream infections (BSI) in the Skåne region, South Sweden. A control group consisted of patients with positive stool cultures/PCR for Salmonella but without BSI. Data were collected following a predefined study protocol from medical records. Standardized statistical analyses assessed patient characteristics, clinical presentation, and outcomes.

RESULTS

Between 2012 and 2022, 149 patients with SBSI were identified, with the majority having non-typhoidal Salmonella (NTS) infections (95%). A declining trend in the incidence of SBSI was observed, with the highest incidence in 2012 (1.5 per 100,000 person-years) and the lowest in 2020 (0.3 per 100,000 person-years). Patients with BSI were more likely to be older, have comorbidities, be immunosuppressed, and use proton pump inhibitors (PPIs). Additionally, patients with BSI presented with fewer gastrointestinal symptoms, had a higher respiratory rate, lower saturation, and higher SOFA scores, suggesting a more septic presentation. Patients with SBSI had significantly longer hospital stays and higher 30-day, 90-day, 180-day, and 365-day mortality rates compared to the control group.

CONCLUSION

Invasive Salmonella infections are rare in South Sweden. In a cohort of enteric and invasive Salmonella infection, the absence of classic gastroenteritis symptoms increases the risk of Salmonella bloodstream infection. This study highlights the importance of distinguishing between clinical presentations to guide appropriate treatment when Salmonella infection is suspected. The declining trend in incidence, particularly associated with international travel, necessitates further investigation to understand contributing factors.

Ophthalmic implications of biological threat agents according to the chemical, biological, radiological, nuclear, and explosives framework

As technology continues to evolve, the possibility for a wide range of dangers to people, organizations, and countries escalate globally. The United States federal government classifies types of threats with the capability of inflicting mass casualties and societal disruption as Chemical, Biological, Radiological, Nuclear, and Energetics/Explosives (CBRNE). Such incidents encompass accidental and intentional events ranging from weapons of mass destruction and bioterrorism to fires or spills involving hazardous or radiologic material. All of these have the capacity to inflict death or severe physical, neurological, and/or sensorial disabilities if injuries are not diagnosed and treated in a timely manner. Ophthalmic injury can provide important insight into understanding and treating patients impacted by CBRNE agents; however, improper ophthalmic management can result in suboptimal patient outcomes. This review specifically addresses the biological agents the Center for Disease Control and Prevention (CDC) deems to have the greatest capacity for bioterrorism. CBRNE biological agents, encompassing pathogens and organic toxins, are further subdivided into categories A, B, and C according to their national security threat level. In our compendium of these biological agents, we address their respective CDC category, systemic and ophthalmic manifestations, route of transmission and personal protective equipment considerations as well as pertinent vaccination and treatment guidelines.

The Background, Role and Approach for Development of a Controlled Human Infection Model for Nontyphoidal Salmonella

Nontyphoidal Salmonella (NTS) is responsible for a major global burden of disease and economic loss, particularly in low- and middle-income countries. It is designated a priority pathogen by the WHO for vaccine development and, with new impetus from vaccine developers, the establishment of an NTS controlled human infection model (CHIM) is timely and valuable. The broadly dichotomous clinical presentations of diarrhoea and invasive disease, commonly bacteraemia, present significant challenges to the development of an NTS CHIM. Nevertheless, if successful, such a CHIM will be invaluable for understanding the pathogenesis of NTS disease, identifying correlates of protection and advancing candidate vaccines towards licensure. This article describes the background case for a CHIM for NTS, the role of such a CHIM and outlines a potential approach to its development.

Salmonella Vaccine Study in Oxford (SALVO) trial: protocol for an observer-participant blind randomised placebo-controlled trial of the iNTS-GMMA vaccine within a European cohort

INTRODUCTION

Invasive non-typhoidal Salmonellosis (iNTS) is mainly caused by Salmonella enterica serovars Typhimurium and Enteritidis and is estimated to result in 77 500 deaths per year, disproportionately affecting children under 5 years of age in sub-Saharan Africa. Invasive non-typhoidal Salmonellae serovars are increasingly acquiring resistance to first-line antibiotics, thus an effective vaccine would be a valuable tool in reducing morbidity and mortality from infection. While NTS livestock vaccines are in wide use, no licensed vaccines exist for use in humans. Here, a first-in-human study of a novel vaccine (iNTS-GMMA) containing S. Typhimurium and S. Enteritidis Generalised Modules for Membrane Antigens (GMMA) outer membrane vesicles is presented.

METHOD AND ANALYSIS

The Salmonella Vaccine Study in Oxford is a randomised placebo-controlled participant-observer blind phase I study of the iNTS-GMMA vaccine. Healthy adult volunteers will be randomised to receive three intramuscular injections of the iNTS-GMMA vaccine, containing equal quantities of S. Typhimurium and S. Enteritidis GMMA particles adsorbed on Alhydrogel, or an Alhydrogel placebo at 0, 2 and 6 months. Participants will be sequentially enrolled into three groups: group 1, 1:1 randomisation to low dose iNTS-GMMA vaccine or placebo; group 2, 1:1 randomisation to full dose iNTS-GMMA vaccine or placebo; group 3, 2:1 randomisation to full dose or lower dose (dependant on DSMC reviews of groups 1 and 2) iNTS-GMMA vaccine or placebo.The primary objective is safety and tolerability of the vaccine. The secondary objective is immunogenicity as measured by O-antigen based ELISA. Further exploratory objectives will characterise the expanded human immune profile.

ETHICS AND DISSEMINATION

Ethical approval for this study has been obtained from the South Central-Oxford A Research Ethics Committee (Ethics REF:22/SC/0059). Appropriate documentation and regulatory approvals have been acquired. Results will be disseminated via peer-reviewed articles and conferences.

TRIAL REGISTRATION NUMBER

EudraCT Number: 2020-000510-14.

Induction of Broad Immunity against Invasive Salmonella Disease by a Quadrivalent Combination Salmonella MAPS Vaccine Targeting Salmonella Enterica Serovars Typhimurium, Enteritidis, Typhi, and Paratyphi A

Bloodstream infections in low- and middle-income countries (LMICs) are most frequently attributed to invasive Salmonella disease caused by four primary serovars of Salmonella enterica: Typhi, Paratyphi A, Typhimurium, and Enteritidis. We showed previously that a bivalent vaccine targeting S. Typhi and S. Paratyphi A using a Multiple Antigen-Presenting System (MAPS) induced functional antibodies against S. Typhi and S. Paratyphi. In the current study, we describe the preclinical development of a first candidate quadrivalent combination Salmonella vaccine with the potential to cover all four leading invasive Salmonella serotypes. We showed that the quadrivalent Salmonella MAPS vaccine, containing Vi from S. Typhi, O-specific Polysaccharide (OSP) from S. Paratyphi A, S. Enteritidis and S. Typhimurium, combined with the Salmonella-specific protein SseB, elicits robust and functional antibody responses to each of the components of the vaccine. Our data indicates that the application of MAPS technology to the development of vaccines targeting invasive forms of Salmonella is practical and merits additional consideration.

A genomic appraisal of invasive Salmonella Typhimurium and associated antibiotic resistance in sub-Saharan Africa

Invasive non-typhoidal Salmonella (iNTS) disease manifesting as bloodstream infection with high mortality is responsible for a huge public health burden in sub-Saharan Africa. Salmonella enterica serovar Typhimurium (S. Typhimurium) is the main cause of iNTS disease in Africa. By analysing whole genome sequence data from 1303 S. Typhimurium isolates originating from 19 African countries and isolated between 1979 and 2017, here we show a thorough scaled appraisal of the population structure of iNTS disease caused by S. Typhimurium across many of Africa's most impacted countries. At least six invasive S. Typhimurium clades have already emerged, with ST313 lineage 2 or ST313-L2 driving the current pandemic. ST313-L2 likely emerged in the Democratic Republic of Congo around 1980 and further spread in the mid 1990s. We observed plasmid-borne as well as chromosomally encoded fluoroquinolone resistance underlying emergences of extensive-drug and pan-drug resistance. Our work provides an overview of the evolution of invasive S. Typhimurium disease, and can be exploited to target control measures.

Seroprevalence of non-typhoidal Salmonella disease and associated factors in children in Mukuru settlement in Nairobi County, Kenya

Non-typhoidal Salmonella (NTS) infections remain a significant public health challenge especially in sub-Saharan Africa. NTS disease is endemic in Kenya and is associated with sporadic fatal outbreaks in several regions of the country with poor resource setting. Data is limited on background exposure of NTS in the population in endemic areas and the general immune status of the community most affected by NTS. The aim of the study was to determine the proportion of children exposed to Salmonella Enteritidis or Salmonella Typhimurium O antigen among the apparently healthy children and patients and the associated host and environmental factors among children attending selected healthcare facilities in Mukuru, Nairobi County, Kenya. A cross-sectional case-control study was conducted among patients and apparently healthy participants aged 0-5 years. Blood was collected and centrifuged to obtain serum. The serum was used to test for the presence of antibodies (IgA, IgG, IgM) against NTS using ELISA. A questionnaire was administered to obtain relevant demographic, socio-economic and healthcare utilization information. A total of 382 children were recruited into the study. The NTS seroprevalence was 12.6%. Among the apparently healthy participants, mean age of those exposed to NTS was 36 months and those not exposed was 27 months. Among patients, the mean age was 39 months and those not exposed was 30 months. The seroprevalence of NTS infection among the apparently healthy was significantly associated with cooking water, washing water and age of the child. Treating water using chlorine or boiling method was identified as being protective against contracting Salmonella Typhimurium/Enteritidis. Among the patients, the proportion of exposure was significantly associated with keeping animals and the chicken count. There is a high exposure to NTS among young children below five years of age and the population has developed immunity to the disease.

Comparative Molecular Analysis and Antigenicity Prediction of an Outer Membrane Protein (ompC) of Non-typhoidal Salmonella Serovars Isolated from Different Food Animals in Lagos, Nigeria

Non-typhoidal Salmonella (NTS) infections occur globally with high morbidity and mortality. The public health challenge caused is exacerbated by increasing rate of antibiotic resistance and absence of NTS vaccine. In this study, we characterized the outer membrane protein C (OmpC) serovars isolated from different food animals and predicted antigenicity. ompC of 27 NTS serovars were amplified by polymerase chain reaction (PCR) and sequenced. Sequence data were analysed and B-cell epitope prediction was done by BepiPred tool. T-cell epitope prediction was done by determining peptide-binding affinities of major histocompatibility complex (MHC) classes I and II using NetMHC pan 2.8 and NetMHC-II pan 3.2, respectively. ompC sequence analysis revealed conserved region among ompCs of Salmonella Serovars. A total of 66.7% of ompCs were stable with instability index value < 40 and molecular weight that ranged from 27 745.47 to 32 714.32 kDa. All ompCs were thermostable and hydrophilic with the exception of S. Pomona (14p) isolate that had ompC with GRAVY value of 0.028 making it hydrophobic. Linear B-cell epitope prediction revealed ability of ompC to elicit humoral immunity. Multiple B-cell epitopes that were exposed and buried were observed on several positions on the ompC sequences. T-cell epitope prediction revealed epitopes with strong binding affinity to MHC-I and -II. Strong binding to human leukocyte antigen (HLA-A) ligands, including HLA-A03:1, HLA-A24:02 and HLA-A26:01 in the case of MHC-I were observed. While binding affinity to H-2 IAs, H-2 IAq and H-2 IAu (H-2 mouse molecules) were strongest in the case of MHC-II. ompCs of NTS serovars isolated from different food animal sources indicated ability to elicit humoral and cell-mediated immunity. Hence, ompCs of NTS serovars are potential candidate for production of NTS vaccines.

Nontyphoidal Salmonella Invasive Disease: Challenges and Solutions

Nontyphoidal Salmonella are a leading cause of community-onset bacteremia and other serious infections in sub-Saharan African countries where large studies indicate that they are an uncommon cause of moderate-to-severe diarrhea. Approximately 535 000 nontyphoidal Salmonella invasive disease illnesses and 77 500 deaths were estimated to occur in 2017; 422 000 (78.9%) illnesses and 66 500 (85.9%) deaths in countries in sub-Saharan Africa. Lineages of Salmonella enterica serovar Typhimurium sequence type (ST) 313 and lineages of Salmonella enterica serovar Enteritidis ST11 dominate as causes of invasive disease. A major reservoir for these specific strains outside of humans has not been identified to date. Human fecal shedding of such strains is common in areas where nontyphoidal Salmonella invasive disease incidence is high. The case-fatality ratio of nontyphoidal Salmonella invasive disease is approximately 15%. Early diagnosis and treatment are needed to avert fatal outcomes. Antimicrobial resistance, including multiple drug resistance, decreased fluoroquinolone susceptibility, and resistance to third-generation cephalosporins, is increasing in prevalence and is likely to further compromise patient outcomes. Naturally acquired immunity against invasive disease develops in children aged >3 years in endemic areas, likely mediated in part by the sequential acquisition of T-cell immunity, followed by antigen-specific immunoglobulin G antibodies. Vaccines in preclinical or clinical development include live-attenuated S. enterica serovar Typhimurium, nontyphoidal S. enterica core and O-polysaccharide glycoconjugates, multiple antigen-presenting system complexes, and generalized modules for membrane antigens vaccines. The latter are in phase I trials in Europe and Africa. Both vaccine use, and other effective, evidence-based nonvaccine interventions, are needed to prevent and control nontyphoidal Salmonella invasive disease.

Human Salmonellosis: A Continuous Global Threat in the Farm-to-Fork Food Safety Continuum

Salmonella is one of the most common zoonotic foodborne pathogens and a worldwide public health threat. Salmonella enterica is the most pathogenic among Salmonella species, comprising over 2500 serovars. It causes typhoid fever and gastroenteritis, and the serovars responsible for the later disease are known as non-typhoidal Salmonella (NTS). Salmonella transmission to humans happens along the farm-to-fork continuum via contaminated animal- and plant-derived foods, including poultry, eggs, fish, pork, beef, vegetables, fruits, nuts, and flour. Several virulence factors have been recognized to play a vital role in attaching, invading, and evading the host defense system. These factors include capsule, adhesion proteins, flagella, plasmids, and type III secretion systems that are encoded on the Salmonella pathogenicity islands. The increased global prevalence of NTS serovars in recent years indicates that the control approaches centered on alleviating the food animals' contamination along the food chain have been unsuccessful. Moreover, the emergence of antibiotic-resistant Salmonella variants suggests a potential food safety crisis. This review summarizes the current state of the knowledge on the nomenclature, microbiological features, virulence factors, and the mechanism of antimicrobial resistance of Salmonella. Furthermore, it provides insights into the pathogenesis and epidemiology of Salmonella infections. The recent outbreaks of salmonellosis reported in different clinical settings and geographical regions, including Africa, the Middle East and North Africa, Latin America, Europe, and the USA in the farm-to-fork continuum, are also highlighted.

Complementary measurement of nontyphoidal Salmonella-specific IgG and IgA antibodies in oral fluid and serum

Objectives

Immuno-epidemiological studies of orally acquired, enteric pathogens such as nontyphoidal Salmonella (NTS) often focus on serological measures of immunity, ignoring potentially relevant oral mucosal responses. In this study we sought to assess the levels and detectability of both oral fluid and serum IgG and IgA to NTS antigens, in endemic and non-endemic populations.

Methods

IgG and IgA antibodies specific for Salmonella Typhimurium and Salmonella Enteritidis O antigen and phase 1 flagellin were assessed using Enzyme Linked Immunosorbent Assay (ELISA). Paired oral fluid and serum samples were collected from groups of 50 UK adults, Kenyan adults and Kenyan infants. Additionally, oral fluid alone was collected from 304 Kenyan individuals across a range of ages.

Results

Antigen-specific IgG and IgA was detectable in the oral fluid of both adults and infants. Oral fluid antibody increased with age, peaking in adulthood for both IgG and IgA but a separate peak was also observed for IgA in infants. Oral fluid and serum responses correlated for IgG but not IgA. Despite standardised collection the relationship between oral fluid volume and antibody levels varied with age and country of origin.

Conclusions

Measurement of NTS-specific oral fluid antibody can be used to complement measurement of serum antibody. For IgA in particular, oral fluid may offer insights into how protective immunity to NTS changes as individuals transition with age, from maternal to acquired systemic and mucosal immunity. This may prove useful in helping to guide future vaccine design.

The rpoS gene confers resistance to low osmolarity conditions in Salmonella enterica serovar Typhi

Salmonella enterica serovars Typhimurium and Typhi are enteropathogens that differ in host range and the diseases that they cause. We found that exposure to a combination of hypotonicity and the detergent Triton X-100 significantly reduced the viability of the S. Typhi strain Ty2 but had no effect on the S. Typhimurium strain SL1344. Further analysis revealed that hypotonicity was the critical factor: incubation in distilled water alone was sufficient to kill Ty2, while the addition of sodium chloride inhibited killing in a dose-dependent manner. Ty2's loss of viability in water was modified by culture conditions: bacteria grown in well-aerated shaking cultures were more susceptible than bacteria grown under less aerated static conditions. Ty2, like many S. Typhi clinical isolates, has an inactivating mutation in the rpoS gene, a transcriptional regulator of stress responses, whereas most S. Typhimurium strains, including SL1344, have the wild-type gene. Transformation of Ty2 with a plasmid expressing wild-type rpoS, but not the empty vector, significantly increased survival in distilled water. Moreover, an S. Typhi strain with wild-type rpoS had unimpaired survival in water. Inactivation of the wild-type gene in this strain significantly reduced survival, while replacement with an arabinose-inducible allele of rpoS restored viability in water under inducing conditions. Our observations on rpoS-dependent differences in susceptibility to hypotonic conditions may be relevant to the ability of S. Typhi and S. Typhimurium to tolerate the various environments they encounter during the infectious cycle. They also have implications for the handling of these organisms during experimental manipulations.

The CRISPR genotypes and genetic diversity of different serogroups of nontyphoidal Salmonella in Guizhou Province, 2013-2018

Nontyphoidal Salmonella is a bacterial and foodborne pathogen that poses a severe public health threat. However, the genetic diversity of different serogroups of nontyphoidal Salmonella in Guizhou is unknown. This study aimed to obtain the RNA secondary structure of the typical direct repeat sequences, the characteristics of clustered regularly interspaced short palindromic repeats (CRISPR) genotypes, and the genetic diversity of different serogroups of nontyphoidal Salmonella strains. The 342 nontyphoidal Salmonella strains were collected from nine cities (prefectures) of Guizhou province during 2013-2018, serotyped by slide agglutination, and examined the molecular genotypes by CRISPR method. The strains were divided into five serogroups. The dominant serogroup was group B (47.08%), followed by group D1 (36.55%). One hundred and thirty-five CRISPR genotypes were detected with 108 novel spacer sequences amongst 981 unique spacer sequences. The diversity of nontyphoidal Salmonella CRISPR loci was not only the deletion, duplication, or point mutation of spacer sequences but also the acquisition of new spacer sequences to form novel genotypes. The CRISPR genotyping was an effective typing method that could reveal the genetic diversity of different nontyphoidal Salmonella serotypes except for S. Enteritidis.

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.

Uptake of Plasmodium chabaudi hemozoin drives Kupffer cell death and fuels superinfections

Kupffer cells (KCs) are self-maintained tissue-resident macrophages that line liver sinusoids and play an important role on host defense. It has been demonstrated that upon infection or intense liver inflammation, KCs might be severely depleted and replaced by immature monocytic cells; however, the mechanisms of cell death and the alterations on liver immunity against infections deserves further investigation. We explored the impact of acute Plasmodium infection on KC biology and on the hepatic immune response against secondary infections. Similar to patients, infection with Plasmodium chabaudi induced acute liver damage as determined by serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) elevation. This was associated with accumulation of hemozoin, increased of proinflammatory response and impaired bacterial and viral clearance, which led to pathogen spread to other organs. In line with this, mice infected with Plasmodium had enhanced mortality during secondary infections, which was associated with increased production of mitochondrial superoxide, lipid peroxidation and increased free iron within KCs-hallmarks of cell death by ferroptosis. Therefore, we revealed that accumulation of iron with KCs, triggered by uptake of circulating hemozoin, is a novel mechanism of macrophage depletion and liver inflammation during malaria, providing novel insights on host susceptibility to secondary infections. Malaria can cause severe liver damage, along with depletion of liver macrophages, which can predispose individuals to secondary infections and enhance the chances of death.

Multiple immunodominant O-epitopes co-expression in live attenuated Salmonella serovars induce cross-protective immune responses against S. Paratyphi A, S. Typhimurium and S. Enteritidis

Salmonella enterica subsp. enterica (S. enterica) is a significant public health concern and is estimated to cause more than 300,000 deaths annually. Nowadays, the vaccines available for human Salmonellosis prevention are all targeting just one serovar, i.e., S. Typhi, leaving a huge potential risk of Salmonella disease epidemiology change. In this study, we explored the strategy of multiple immunodominant O-epitopes co-expression in S. enterica serovars and evaluated their immunogenicity to induce cross-immune responses and cross-protections against S. Paratyphi A, S. Typhimurium and S. Enteritidis. We found that nucleotide sugar precursors CDP-Abe and CDP-Par (or CDP-Tyv) could be utilized by S. enterica serovars simultaneously, exhibiting O2&O4 (or O4&O9) double immunodominant O-serotypes without obvious growth defects. More importantly, a triple immunodominant O2&O4&O9 O-serotypes could be achieved in S. Typhimurium by improving the substrate pool of CDP-Par, glycosyltransferase WbaV and flippase Wzx via a dual-plasmid overexpressing system. Through immunization in a murine model, we found that double or triple O-serotypes live attenuated vaccine candidates could induce significantly higher heterologous serovar-specific antibodies than their wild-type parent strain. Meanwhile, the bacterial agglutination, serum bactericidal assays and protection efficacy experiments had all shown that these elicited serum antibodies are cross-reactive and cross-protective. Our work highlights the potential of developing a new type of live attenuated Salmonella vaccines against S. Paratyphi A, S. Typhimurium and S. Enteritidis simultaneously.

Urban rats as carriers of invasive Salmonella Typhimurium sequence type 313, Kisangani, Democratic Republic of Congo

BACKGROUND

Invasive non-typhoidal Salmonella (iNTS-mainly serotypes Enteritidis and Typhimurium) are major causes of bloodstream infections in children in sub-Saharan Africa, but their reservoir remains unknown. We assessed iNTS carriage in rats in an urban setting endemic for iNTS carriage and compared genetic profiles of iNTS from rats with those isolated from humans.

METHODOLOGY/PRINCIPAL FINDINGS

From April 2016 to December 2018, rats were trapped in five marketplaces and a slaughterhouse in Kisangani, Democratic Republic of the Congo. After euthanasia, blood, liver, spleen, and rectal content were cultured for Salmonella. Genetic relatedness between iNTS from rats and humans-obtained from blood cultures at Kisangani University Hospital-was assessed with multilocus variable-number tandem repeat (VNTR) analysis (MLVA), multilocus sequence typing (MLST) and core-genome MLST (cgMLST). 1650 live-capture traps yielded 566 (34.3%) rats (95.6% Rattus norvegicus, 4.4% Rattus rattus); 46 (8.1%) of them carried Salmonella, of which 13 had more than one serotype. The most common serotypes were II.42:r:- (n = 18 rats), Kapemba (n = 12), Weltevreden and Typhimurium (n = 10, each), and Dublin (n = 8). Salmonella Typhimurium belonged to MLST ST19 (n = 7 rats) and the invasive ST313 (n = 3, isolated from deep organs but not from rectal content). Sixteen human S. Typhimurium isolates (all ST313) were available for comparison: MLVA and cgMLST revealed two distinct rat-human clusters involving both six human isolates, respectively, i.e. in total 12/16 human ST313 isolates. All ST313 Typhimurium isolates from rats and humans clustered with the ST313 Lineage 2 isolates and most were multidrug resistant; the remaining isolates from rats including S. Typhimurium ST19 were pan-susceptible.

CONCLUSION

The present study provides evidence of urban rats as potential reservoirs of S. Typhimurium ST313 in an iNTS endemic area in sub-Saharan Africa.

Multilayered Networks of SalmoNet2 Enable Strain Comparisons of the Salmonella Genus on a Molecular Level

Serovars of the genus Salmonella primarily evolved as gastrointestinal pathogens in a wide range of hosts. Some serotypes later evolved further, adopting a more invasive lifestyle in a narrower host range associated with systemic infections. A system-level knowledge of these pathogens could identify the complex adaptations associated with the evolution of serovars with distinct pathogenicity, host range, and risk to human health. This promises to aid the design of interventions and serve as a knowledge base in the Salmonella research community. Here, we present SalmoNet2, a major update to SalmoNet1, the first multilayered interaction resource for Salmonella strains, containing protein-protein, transcriptional regulatory, and enzyme-enzyme interactions. The new version extends the number of Salmonella networks from 11 to 20. We now include a strain from the second species in the Salmonella genus, a strain from the Salmonella enterica subspecies arizonae and additional strains of importance from the subspecies enterica, including S. Typhimurium strain D23580, an epidemic multidrug-resistant strain associated with invasive nontyphoidal salmonellosis (iNTS). The database now uses strain specific metabolic models instead of a generalized model to highlight differences between strains. The update has increased the coverage of high-quality protein-protein interactions, and enhanced interoperability with other computational resources by adopting standardized formats. The resource website has been updated with tutorials to help researchers analyze their Salmonella data using molecular interaction networks from SalmoNet2. SalmoNet2 is accessible at http://salmonet.org/. IMPORTANCE Multilayered network databases collate interaction information from multiple sources, and are powerful both as a knowledge base and subject of analysis. Here, we present SalmoNet2, an integrated network resource containing protein-protein, transcriptional regulatory, and metabolic interactions for 20 Salmonella strains. Key improvements to the update include expanding the number of strains, strain-specific metabolic networks, an increase in high-quality protein-protein interactions, community standard computational formats to help interoperability, and online tutorials to help users analyze their data using SalmoNet2.

Genetic and Structural Variation in the O-Antigen of Salmonella enterica Serovar Typhimurium Isolates Causing Bloodstream Infections in the Democratic Republic of the Congo

Salmonella enterica serovar Typhimurium causes a devastating burden of invasive disease in sub-Saharan Africa with high levels of antimicrobial resistance. No licensed vaccine is available, but O-antigen-based candidates are in development, as the O-antigen moiety of lipopolysaccharides is the principal target of protective immunity. The vaccines under development are designed based on isolates with O-antigen O-acetylated at position C-2 of abequose, giving the O:5 antigen. Serotyping data on recent Salmonella Typhimurium clinical isolates from the Democratic Republic of the Congo (DRC), however, indicate increasing levels of isolates without O:5. The importance and distribution of this loss of O:5 antigen in the population as well as the genetic mechanism responsible for the loss and chemical characteristics of the O-antigen are poorly understood. In this study, we Illumina whole-genome sequenced 354 Salmonella Typhimurium isolates from the DRC, which were isolated between 2002 and 2017. We used genomics and phylogenetics combined with chemical approaches (¹H nuclear magnetic resonance [NMR], high-performance anion-exchange chromatography with pulsed amperometric detection [HPAEC-PAD], high-performance liquid chromatography–PAD [HPLC-PAD], and HPLC-size exclusion chromatography [HPLC-SEC]) to characterize the O-antigen features within the bacterial population. We observed convergent evolution toward the loss of the O:5 epitope predominantly caused by recombination events in a single gene, the O-acetyltransferase gene oafA. In addition, we observe further O-antigen variations, including O-acetylation of the rhamnose residue, different levels of glucosylation, and the absence of O-antigen repeating units. Large recombination events underlying O-antigen variation were resolved using long-read MinION sequencing. Our study suggests evolutionary pressure toward O-antigen variants in a region where invasive disease by Salmonella Typhimurium is highly endemic. This needs to be taken into account when developing O-antigen-based vaccines, as it might impact the breadth of coverage in such regions.

Antimicrobial Resistance Rates and Surveillance in Sub-Saharan Africa: Where Are We Now?

Introduction

Although antimicrobials have traditionally been used to treat infections and improve health outcomes, resistance to commonly used antimicrobials has posed a major challenge. An estimated 700,000 deaths occur globally every year as a result of infections caused by antimicrobial-resistant pathogens. Antimicrobial resistance (AMR) also contributes directly to the decline in the global economy. In 2019, sub-Saharan Africa (SSA) had the highest mortality rate (23.5 deaths per 100,000) attributable to AMR compared to other regions.

Methods

We searched PubMed for articles relevant to AMR in pathogens in the WHO-GLASS list and in other infections of local importance in SSA. In this review, we focused on AMR rates and surveillance of AMR for these priority pathogens and some of the most encountered pathogens of public health significance. In addition, we reviewed the implementation of national action plans to mitigate against AMR in countries in SSA.

Results and Discussion

The SSA region is disproportionately affected by AMR, in part owing to the prevailing high levels of poverty, which result in a high burden of infectious diseases, poor regulation of antimicrobial use, and a lack of alternatives to ineffective antimicrobials. The global action plan as a strategy for prevention and combating AMR has been adopted by most countries, but fewer countries are able to fully implement country-specific action plans, and several challenges exist in many settings.

Conclusion

A concerted One Health approach will be required to ramp up implementation of action plans in the region. In addition to AMR surveillance, effective implementation of infection prevention and control, water, sanitation, and hygiene, and antimicrobial stewardship programs will be key cost-effective strategies in helping to tackle AMR.

Whole Genome Sequencing, Antibiotic Resistance, and Epidemiology Features of Nontyphoidal Salmonella Isolated From Diarrheic Children: Evidence From North China

Nontyphoidal Salmonella (NTS) in children remains a growing burden on public health and often causes children to be hospitalized with diarrheic symptoms. In this work, 260 strains of human Salmonella isolated from Jilin, China were characterized by serotypes and antimicrobial resistance using whole genome sequencing (WGS). The most prevalent serotype was Salmonella enteritidis (47.3%), followed by S. I 4,[5],12:i:- (33.1%), and Salmonella Typhimurium (7.3%). Furthermore, the consistency between resistance phenotype and genotype was confirmed. Similarly, strains harbored bla_TEM−1B and tetA genes were detected, which verified the level of resistant phenotype in β-lactams and tetracyclines. The presence of a single mutation in parC, gyrA, and qnrS1 genes corresponding to quinolones was also observed. In our work, multilocus sequence typing (MLST) and core genome multilocus sequence typing (cgMLST) were found to have a high resolution to molecular traceability, and the combination of both was conducive to practical application in an actual situation. Taking all of this into account, we suggested that the comprehensive surveillance of Salmonella infection in children should be carried out to monitor antimicrobial-resistant trends from various sources and to alert on outbreaks of foodborne diseases to protect public health.

Complications and mortality of non-typhoidal salmonella invasive disease: a global systematic review and meta-analysis

BACKGROUND

Non-typhoidal salmonella can cause serious, life-threatening invasive infections involving the bloodstream and other normally sterile sites. We aimed to systematically review the prevalence of complications and case-fatality ratio (CFR) of non-typhoidal salmonella invasive disease to provide contemporary global estimates and inform the development of vaccine and non-vaccine interventions.

METHODS

We did a global systematic review and meta-analysis of studies investigating the complications and mortality associated with non-typhoidal salmonella invasive disease. We searched Embase, MEDLINE, Web of Science, and PubMed for peer-reviewed, primary research articles published from database inception up to June 4, 2021, with no restrictions on language, country, date, or participant demographics. Only studies reporting the proportion of complications or deaths associated with non-typhoidal salmonella invasive disease, confirmed by culture of samples taken from a normally sterile site (eg, blood or bone marrow) were included. We excluded case reports, case series, policy reports, commentaries, editorials, and conference abstracts. Data on the prevalence of complications and CFR were abstracted. The primary outcomes were to estimate the prevalence of complications and CFR of non-typhoidal salmonella invasive disease. We calculated an overall pooled CFR estimate and pooled CFR stratified by UN region, subregion, age group, and by serovar when available with a random-effects meta-analysis. A risk-of-bias assessment was done, and heterogeneity was assessed with Cochran's Q Test, I2, and τ2. This study was done in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses, and is registered with PROSPERO, CRD42020202293.

FINDINGS

The systematic review returned a total of 8770 records. After duplicates were removed, 5837 titles and abstracts were screened, yielding 84 studies from 35 countries after exclusions. Of these included studies, 77 (91·7%) were hospital-based and 66 (78·6%) were located in Africa or Asia. Among 55 studies reporting non-typhoidal salmonella disease-associated complications, a total of 45 different complications were reported and 1824 complication events were identified among 6974 study participants. The most prevalent complication was septicaemia, occurring in 171 (57·2%) of 299 participants, followed by anaemia in 580 (47·3%) of 1225 participants. From 81 studies reporting the CFR of non-typhoidal salmonella invasive disease, the overall pooled CFR estimate was 14·7% (95% CI 12·2-17·3). When stratified by UN region, the pooled CFR was 17·1% (13·6-21·0) in Africa, 14·0% (9·4-19·4) in Asia, 9·9% (6·4-14·0) in Europe, and 9·6% (0·0-25·1) in the Americas. Of all 84 studies, 66 (78·6%) had an overall high risk of bias, 18 (21·4%) had a moderate risk, and none had a low risk. Substantial heterogeneity (I2>80%) was observed in most (15 [65·2%] of 23) CFR estimates.

INTERPRETATION

Complications were frequent among individuals with non-typhoidal salmonella invasive disease and approximately 15% of patients died. Clinicians, especially in African countries, should be aware of non-typhoidal salmonella invasive disease as a cause of severe febrile illness. Prompt diagnoses and management decisions, including empiric antimicrobial therapy, would improve patient outcomes. Additionally, investments in improving clinical microbiology facilities to identify non-typhoidal salmonella and research efforts towards vaccine development and non-vaccine prevention measures would prevent non-typhoidal salmonella invasive disease-associated illness and death.

FUNDING

EU Horizon 2020 research and innovation programme.

Environmental protection based on the nanobiosensing of bacterial lipopolysaccharides (LPSs): material and method overview

Lipopolysaccharide (LPS) or endotoxin control is critical for environmental and healthcare issues. LPSs are responsible for several infections, including septic and shock sepsis, and are found in water samples. Accurate and specific diagnosis of endotoxin is one of the most challenging issues in medical bacteriology. Enzyme-linked immunosorbent assay (ELISA), plating and culture-based methods, and Limulus amebocyte lysate (LAL) assay are the conventional techniques in quantifying LPS in research and medical laboratories. However, these methods have been restricted due to their disadvantages, such as low sensitivity and time-consuming and complicated procedures. Therefore, the development of new and advanced methods is demanding, particularly in the biological and medical fields. Biosensor technology is an innovative method that developed extensively in the past decade. Biosensors are classified based on the type of transducer and bioreceptor. So in this review, various types of biosensors, such as optical (fluorescence, SERS, FRET, and SPR), electrochemical, photoelectrochemical, and electrochemiluminescence, on the biosensing of LPs were investigated. Also, the critical role of advanced nanomaterials on the performance of the above-mentioned biosensors is discussed. In addition, the application of different labels on the efficient usage of biosensors for LPS is surveyed comprehensively. Also, various bio-elements (aptamer, DNA, miRNA, peptide, enzyme, antibody, etc.) on the structure of the LPS biosensor are investigated. Finally, bio-analytical parameters that affect the performance of LPS biosensors are surveyed.

Genomics of human and chicken Salmonella isolates in Senegal: Broilers as a source of antimicrobial resistance and potentially invasive nontyphoidal salmonellosis infections

Salmonella enterica is the most common foodborne pathogen worldwide. It causes two types of diseases, a self-limiting gastroenteritis and an invasive, more threatening, infection. Salmonella gastroenteritis is caused by several serotypes and is common worldwide. In contrast, invasive salmonellosis is rare in high-income countries (HIC) while frequent in low- and middle-income countries (LMIC), especially in sub-Saharan Africa (sSA). Invasive Nontyphoidal Salmonella (iNTS), corresponding to serotypes other than Typhi and Paratyphi, have emerged in sSA and pose a significant risk to public health. We conducted a whole-genome sequence (WGS) analysis of 72 strains of Salmonella isolated from diarrheic human patients and chicken meat sold in multipurpose markets in Dakar, Senegal. Antimicrobial susceptibility testing combined with WGS data analysis revealed frequent resistance to fluoroquinolones and the sulfamethoxazole-trimethoprim combination that are among the most used treatments for invasive Salmonella. In contrast, resistance to the historical first-line drugs chloramphenicol and ampicillin, and to cephalosporins was rare. Antimicrobial resistance (AMR) was lower in clinical isolates compared to chicken strains pointing to the concern posed by the excessive use of antimicrobials in farming. Phylogenetic analysis suggested possible transmission of the emerging multidrug resistant (MDR) Kentucky ST198 and serotype Schwarzengrund from chicken to human. These results stress the need for active surveillance of Salmonella and AMR in order to address invasive salmonellosis caused by nontyphoidal Salmonella strains and other important bacterial diseases in sSA.

Virulence Factors and Antimicrobial Resistance in Salmonella Species Isolated from Retail Beef in Selected KwaZulu-Natal Municipality Areas, South Africa

Salmonellosis and antimicrobial resistance caused by non-typhoidal Salmonella are public health concerns. This study aimed at determining prevalence, serovars, virulence factors and antimicrobial resistance of Salmonella from beef products. Four-hundred beef samples from 25 retail outlets in KwaZulu-Natal, South Africa were analyzed for Salmonella using standard methods, confirmation with matrix-assisted laser desorption ionization–time of flight and serotyping according to the White–Kauffmann–Le Minor scheme. The Kirby Bauer disk diffusion method was used to determine antimicrobial resistance against Cefotaxime, Kanamycin, Ampicillin, Amoxicillin, Trimethoprim Sulfamethoxazole, Ciprofloxacin, Chloramphenicol, Gentamicin Cefoxitin and Tetracycline. A polymerase chain reaction was performed to detect invA, agfA, lpfA, hilA, sivH, sefA, sopE, and spvC virulence genes. Salmonella was observed in 1.25% (5/400) of the samples. Four serovars (Enteritidis, Hadar, Heidelberg, Stanley) were identified. Almost all Salmonella were susceptible to all antimicrobials except S. Enteritidis isolate that was resistant to Tetracycline, Ampicillin and Amoxicillin. All Salmonella isolates carried at least two virulence factors. The findings indicate low Salmonella prevalence in meat from selected KZN retail beef; however, routine surveillance to monitor risk associated with virulence factors is required to mitigate potential outbreaks. The resistant S. Enteritidis highlights a need to routinely monitor antimicrobial resistance in order to enhance human health.

The antagonistic interactions between a polyvalent phage SaP7 and β-lactam antibiotics on combined therapies

Phage therapy is a promising alternative antibiotic strategy to combat multidrug-resistant bacteria infections. Most studies focus on the synergistic effects, while the antagonistic interactions between phage and antibiotics is rarely studied. Here, we isolated and identified a novel polyvalent phage SaP7, which is capable of infecting multidrug-resistant Salmonella S7 and several E. coli strains. Morphology via electron microscopy showed that SaP7 belonged to the Myoviridae family. Genomic analysis revealed that the genome of SaP7 lacked any genes associated with antibiotic resistance, toxins, lysogeny, and virulence factors. We discovered the antagonism efficacy of SaP7 combined amoxicillin/potassium clavulanate (AMC) in counteracting Salmonella S7 in piglet-models by bacterial loads in feces and tissues. The consistent result as above between SaP7 and amoxicillin (AMX) was further verified in BALB/c mice-models. Furthermore, in vitro, plaque assay and minimum inhibitory concentration (MIC) determinations showed that AMX or AMC or cefepime (FEP) inhibited SaP7 plaque formation respectively and SaP7 decreased bacterial susceptibility of Salmonella S7 to AMX, AMC and FEP. And the negative interference of SaP7 with the bacteriostasis to Salmonella S7 of these three β-lactam antibiotics was observed in planktonic cultures via microtiter plates, but could not prevent the bacteriostasis of high titer of phage or high concentration of antibiotics. Finally, our research suggested that a polyvalent phage SaP7 existed antagonism with several β-lactam antibiotics. It is therefore crucial to fully and cautiously evaluate phage/antibiotic interactions and probable outcomes to avoid antagonistic impacts and failure of antibiotic and phage combination therapy.

Virulence Gene Profile, Antimicrobial Resistance and Multilocus Sequence Typing of Salmonella enterica Subsp. enterica Serovar Enteritidis from Chickens and Chicken Products

This study was undertaken to determine the virulence, antimicrobial resistance and molecular subtypes of Salmonella in the Central Region of Peninsular Malaysia. A total of 45 Salmonella Enteritidis were detected from live chicken (cloacal swab), and chicken products (fresh and ready-to-eat meat) samples upon cultural isolation and serotyping. Similarly, an antimicrobial susceptibility test based on the Kirby Bauer disk diffusion method as well as antimicrobial resistance AMR genes, virulence determinants and multilocus sequence typing (MLST) typing were conducted after the Whole Genome Sequencing and analysis of the isolates. The results indicate that sequence types ST1925 (63.7%), and ST11 (26.5%) were the predominant out of the seven sequence types identified (ST292, ST329, ST365, ST423 and ST2132). The phenotypic antimicrobial profile corresponds to the genotypic characterization in that the majority of the isolates that exhibited tetracycline, gentamycin and aminoglycoside resistance; they also possessed the tetC and blaTEM β-Lactam resistance genes. However, isolates from cloacal swabs showed the highest number of resistance genes compared to the chicken products (fresh and ready-to-eat meat) samples. Furthermore, most of the virulence genes were found to cluster in the Salmonella pathogenicity island (SPI). In this study, all the isolates were found to possess SPI-1, which codes for the type III secretion system, which functions as actin-binding proteins (SptP and SopE). The virulence plasmid (VP) genes (spvB, spvC) were present in all genotypes except ST365. The findings of this study, particularly with regard to the molecular subtypes and AMR profiles of the Salmonella Enteritidis serotype shows multidrug-resistance features as well as genetic characteristics indicative of high pathogenicity.

An adsorption method to prepare specific antibody-depleted normal human serum as a source of complement for human serum bactericidal assays for Salmonella

Serum bactericidal assays (SBA) are valuable for assessing the functional activity of natural and vaccine-induced antibodies against many Gram-negative bacteria, such as meningococcus and Salmonella. However, SBA often require an exogenous source of complement and the presence of pre-existing naturally acquired antibodies limits the use of human complement for this purpose. To remove pre-existing Salmonella-specific antibodies, in the context of SBA for Salmonella vaccine research, we incubated human sera with preparations of Salmonella. By incubating at 4 °C, pre-existing antibodies were adsorbed onto the Salmonella bacteria with only minimal complement deposition. We assessed the effects of adsorption on specific antibody levels, complement activity and the bactericidal activity of sera using flow cytometry, SBA and haemolytic assays. Adsorption removed Salmonella-specific antibodies and bactericidal activity against Salmonella from whole serum but was not detrimental to serum complement activity, even after five adsorption cycles. Bactericidal activity could be reconstituted in the adsorbed serum by the addition of exogenous specific antibodies. Sera preadsorbed with Salmonella are suitable as a source of human complement to measure the bactericidal activity of Salmonella antibodies. The adsorption method can be used to deplete, simply and rapidly, specific antibodies from serum to prepare a source of human complement for use in SBA for vaccine research and assessment.

Epidemiology, Serogroups and Resistance of Salmonella During a 15-Year Period (2006-2020) in Kuwait

Purpose

The aim of the study was to investigate the changing pattern in serogroup distribution and antimicrobial resistance of all Salmonella spp. isolated from patients attending the Mubarak Al Kabeer Hospital (MAK), Kuwait from 2006 to 2020.

Patients and Methods

A retrospective study of all enrolled patients attending the MAK with culture-positive Salmonella spp. was undertaken. Data on age, gender, culture sample and serogroup were obtained from the laboratory information system. A prospective antimicrobial susceptibility of all stock isolates was carried out using E test. The trend rates of Salmonella serogroups and antimicrobial resistance were compared among 5 periods: 2006–2008, 2009–2011, 2012–2014, 2015–2017, and 2018–2020.

Results

A total of 700 isolates were identified. The majority of the isolates were from the stool (77.6%), followed by the blood (16.4%). The most common serogroups were serogroup D (37.6%) and B (23.4%). There was a significant rise in ciprofloxacin resistance from 32.2% during 2006–2008 to 54.3% during 2018–2020 and from 32.5% during 2009–2011 to 54.3% during 2018–2020 (P=0.0001, respectively). The resistance trend to cefotaxime was at relatively low levels ranging from 0% to 3.4% through 2006–2008 to 2018–2020. There was a significant drop of the resistance to ampicillin from 23.6% in 2015–2017 to 12.3% in 2006–2008 to 2018–2020 (P=0.03). Trimethoprim/sulfamethoxazole resistance dropped significantly from 14.5 to 3.6% (P=0.002) during 2006–2008 to 2018–2020 and then from 13.5 to 3.6% (P=0.02) during 2015–2017 to 2018–2020. One hundred and seventeen (16.7%) isolates were multidrug-resistant.

Conclusion

Continuous surveillance of Salmonella and its antimicrobial resistance is important for antibiotic policy formulation for invasive Salmonella infections.

Direct association between rainfall and non-typhoidal Salmonella bloodstream infections in hospital-admitted children in the Democratic Republic of Congo

Non-typhoidal Salmonella (NTS) ranks first among causes of bloodstream infection in children under five years old in the Democratic Republic of Congo and has a case fatality rate of 15%. Main host-associated risk factors are Plasmodium falciparum malaria, anemia and malnutrition. NTS transmission in sub-Saharan Africa is poorly understood. NTS bloodstream infections mostly occur during the rainy season, which may reflect seasonal variation in either environmental transmission or host susceptibility. We hypothesized that environment- and host-associated factors contribute independently to the seasonal variation in NTS bloodstream infections in children under five years old admitted to Kisantu referral hospital in 2013-2019. We used remotely sensed rainfall and temperature data as proxies for environmental factors and hospital data for host-associated factors. We used principal component analysis to disentangle the interrelated environment- and host-associated factors. With timeseries regression, we demonstrated a direct association between rainfall and NTS variation, independent of host-associated factors. While the latter explained 17.5% of NTS variation, rainfall explained an additional 9%. The direct association with rainfall points to environmental NTS transmission, which should be explored by environmental sampling studies. Environmental and climate change may increase NTS transmission directly or via host susceptibility, which highlights the importance of preventive public health interventions.

Incidence of non-typhoidal Salmonella invasive disease: A systematic review and meta-analysis

OBJECTIVES

We sought to collate and summarize high-quality data on non-typhoidal Salmonella invasive disease (iNTS) incidence to provide contemporary incidence estimates by location and year.

METHODS

We systematically searched the databases Embase + MEDLINE, Web of Science, and PubMed for articles published on the incidence of iNTS from inception of the database through 8 May 2020 with no language, country, date, or demographic restrictions applied. A meta-analysis was performed to report pooled iNTS incidence as a rate of cases per 100,000 per year.

RESULTS

Among 13 studies eligible for analysis, there were 68 estimates of incidence. Overall pooled incidence (95% CI) was 44.8 (31.5-60.5) per 100,000 persons per year. When stratified by region, pooled incidence was significantly higher in Africa than Asia, 51.0 (36.3-68.0) compared to 1.0 (0.2-2.5), respectively. Incidence was consistently higher in children aged <5 years compared with older age groups. Incidence displayed considerable heterogeneity in both place and time, varying substantially between locations and over consecutive years in the same location.

CONCLUSIONS

iNTS incidence varies by region, location, age group, and over time. Concerted efforts are needed to address the limited high-quality data available on iNTS disease incidence.