Invasive nontyphoidal Salmonella disease: epidemiology, pathogenesis and diagnosis

Clinical-Microbiological Study of Nontyphoidal Salmonella Infections from Karnataka, India

Background

Nontyphoidal salmonella (NTS) are responsible for food-borne gastroenteritis and bacteremia, in immunosuppressed individuals. Antibiotic resistance in NTS is on the rise. This study reports the prevalence and antimicrobial susceptibility of nontyphoidal salmonella in clinical samples. Study Design. This is a hospital record-based cross-sectional, retrospective study.

Methods

In our study, inpatient samples such as blood (n = 13546), urine (n = 11,333), pus (n = 1,010), and stool (n = 926) samples were cultured to isolate etiological agents in the microbiology department from January 2017 to June 2019. Relevant details such as duration of fever, platelet count, hemoglobin, WBC count, immune status, and mode of treatment were noted from the medical records. Data were analyzed, and continuous variables were expressed as mean and categorical variables as percentages.

Results

A total of 24 NTS serovars were isolated, which included ten isolates from blood, five each from urine and pus, and four from stool samples. Of the NTS, five were Salmonella enterica subsp. enterica, three were S.enterica serovar Typhimurium, one was S.enterica subsp. diarizonae, and 15 S.enterica serovars could not be serologically differentiated. All were susceptible to ampicillin, chloramphenicol, and cefuroxime. However, 16.6% of NTS was resistant to ceftriaxone, 4% to cotrimoxazole, 58% to ciprofloxacin, and 75% to nalidixic acid.

Conclusions

A low prevalence of NTS responsible for invasive infections is seen in this part of the country. Few isolates were resistant to more than one antibiotic. A higher rate of resistance to ceftriaxone is the cause of concern. Awareness of the distribution of NTS serogroups is of epidemiological and public health significance.

Prevalence and Antimicrobial Resistance Diversity of Salmonella Isolates in Jiaxing City, China

Nontyphoidal Salmonella (NTS) is a cause of foodborne diarrheal diseases worldwide. Important emerging NTS serotypes that have spread as multidrug-resistant high-risk clones include S. Typhimurium monophasic variant and S. Kentucky. In this study, we isolated Salmonella in 5019 stool samples collected from patients with clinical diarrhea and 484 food samples. Antibiotic susceptibility testing and whole-genome sequencing were performed on positive strains. The detection rates of Salmonella among patients with diarrhea and food samples were 4.0% (200/5019) and 3.1% (15/484), respectively. These 215 Salmonella isolates comprised five main serotypes, namely S. Typhimurium monophasic variant, S. Typhimurium, S. London, S. Enteritidis, and S. Rissen, and were mainly resistant to ampicillin, tetracycline, chloramphenicol, and trimethoprim/sulfamethoxazole. The MDR rates of five major serotypes were 77.4%, 56.0%, 66.7%, 53.3%, and 80.0%, respectively. The most commonly acquired extended-spectrum β-lactamase-encoding genes were blaTEM-1B, blaOXA-10, and blaCTX-M-65. The S. Typhimurium monophasic variant strains from Jiaxing City belonged to a unique clone with broad antibiotic resistance. S. Kentucky isolates showed the highest drug resistance, and all were MDR strains. The discovery of high antibiotic resistance rates in this common foodborne pathogen is a growing concern; therefore, ongoing surveillance is crucial to effectively monitor this pathogen.

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.

Anti-interferon-gamma autoantibody and salmonellosis: Case report and literature review

Adult-onset immunodeficiency syndrome is characterized by the presence of anti-interferon-gamma (IFN-γ) autoantibody and the distribution of infections. Here, we describe Salmonella enterica bacteremia in a Thai woman who also had anti-IFN-γ autoantibody. The patient was also suffering from Salmonella osteomyelitis and a peri-orbital abscess. Her symptoms were completely eradicated after surgical intervention and the administration of appropriate antibiotics.

The global transcriptomes of Salmonella enterica serovars Gallinarum, Dublin and Enteritidis in the avian host

Salmonella enterica serovar Gallinarum causes Fowl Typhoid in poultry, and it is host specific to avian species. The reasons why S. Gallinarum is restricted to avians, and at the same time predominately cause systemic infections in these hosts, are unknown. In the current study, we developed a surgical approach to study gene expression inside the peritoneal cavity of hens to shed light on this. Strains of the host specific S. Gallinarum, the cattle-adapted S. Dublin and the broad host range serovar, S. Enteritidis, were enclosed in semi-permeable tubes and surgically placed for 4 h in the peritoneal cavity of hens and for control in a minimal medium at 41.2 °C. Global gene-expression under these conditions was compared between serovars using tiled-micro arrays with probes representing the genome of S. Typhimurium, S. Dublin and S. Gallinarum. Among other genes, genes of SPI-13, SPI-14 and the macrophage survival gene mig-14 were specifically up-regulated in the host specific serovar, S. Gallinarum, and further studies into the role of these genes in host specific infection are highly indicated. Analysis of pathways and GO-terms, which were enriched in the host specific S. Gallinarum without being enriched in the two other serovars indicated that host specificity was characterized by a metabolic fine-tuning as well as unique expression of virulence associated pathways. The cattle adapted serovar S. Dublin differed from the two other serovars by a lack of up-regulation of genes encoded in the virulence associated pathogenicity island 2, and this may explain the inability of this serovar to cause disease in poultry.

Multidrug-Resistant Salmonella Species and Their Mobile Genetic Elements from Poultry Farm Environments in Malaysia

The prevalence and persistent outbreaks of multidrug-resistant (MDR) Salmonella in low-income countries have received growing attention among the public and scientific community. Notably, the excessive use of antibiotics in chicken feed for the purpose of treatment or as prophylaxis in the poultry industry have led to a rising rate of antimicrobial resistance. Therefore, this study aimed to determine the presence of antimicrobial-resistant Salmonella species and its mobile genetic elements from soil and effluent samples of 33 randomly selected poultry farms in Selangor, Malaysia. Salmonella species were isolated on selective media (CHROMagar™ Salmonella). VITEK® 2 system was used to identify the isolates and their antimicrobial susceptibility. Subsequently, eight isolates were subjected to the whole genome sequencing (WGS). Based on the results, Salmonella spp. was detected in 38.1% (24/63) of samples, with the highest resistance to ampicillin (62.5%), followed by ampicillin/sulbactam (50.0%) and ciprofloxacin (45.8%). Meanwhile, the identified serovars were Salmonella enterica subspecies enterica serovar Weltevreden (S. Weltevreden), S. Jedburgh, and S. Brancaster. The most prevalent resistance genes detected include qnrS1, blaTEM-176, dfrA14, and tet(A). The IncX1 plasmid, with encoded resistance genes, was also detected in four isolates. Furthermore, mutations in the quinolone resistant-determining regions (QRDR) were discovered, specifically in the gyrA, gyrB, and parC genes. In short, surveillance such as continuous monitoring of antimicrobial resistance and emerging trends in resistance patterns through farm environmental samples could provide information to formulate public health interventions for effective infection prevention and disease control.

Vaccination and Trust in the National Health System among HIV+ Patients: An Italian Cross-Sectional Survey

BACKGROUND

This study aimed to evaluate the knowledge, attitudes, and practises (KAP) of individuals living with HIV (PLWH) regarding vaccines and their trust in the Italian national health system (NHS).

METHODS

A cross-sectional survey was conducted at Amedeo di Savoia Hospital in Turin, Italy, involving 160 HIV-positive patients. Descriptive statistics were utilised to analyse variables such as vaccination status and intention, perceived risk of infection, and disease severity. The infections were categorised into sexually transmitted diseases and other vaccine-preventable diseases.

RESULTS

Except for the perceived severity of infection, there were no significant differences in the percentages between the two infection groups for the variables examined. Concerning patients' perception of the Italian NHS, a high percentage of the sample believed in the information provided by healthcare workers (HCWs) (95.6%) and considered HCWs up-to-date on vaccines (93.1%). However, a considerable proportion expressed concerns about insufficient information on vaccine risks from HCWs (33.3%), perceived judgement by HCWs for vaccine refusal (40.3%), and suspected financial interests of HCWs in vaccination (19.5%).

CONCLUSIONS

Some HIV+ patients may hesitate to be vaccinated or hold misconceptions about the severity of certain infectious diseases. Additionally, there are concerns about trust in the Italian NHS and communication by HCWs.

Antimicrobial resistance and virulence genes of invasive Salmonella enterica from children with bacteremia in north-central Nigeria

Objectives

Bacteremia due to invasive Salmonella enterica has been reported earlier in children in Nigeria. This study aimed to detect the virulence and antibiotic resistance genes of invasive Salmonella enterica from children with bacteremia in north-central Nigeria.

Method

From June 2015 to June 2018, 4163 blood cultures yielded 83 Salmonella isolates. This is a secondary cross-sectional analysis of the Salmonella isolates. The Salmonella enterica were isolated and identified using standard bacteriology protocol. Biochemical identifications of the Salmonella enterica were made by Phoenix MD 50 identification system. Further identification and confirmation were done with polyvalent antisera O and invA gene. Antimicrobial susceptibility testing was done following clinical and laboratory standard institute guidelines. Resistant genes and virulence genes were determined using a real-time polymerase chain reaction.

Result

Salmonella typhi 51 (61.4%) was the most prevalent serovar, followed by Salmonella species 13 (15.7%), choleraesuis 8 (9.6%), enteritidis 6 (7.2%), and typhimurium 5 (6.1%). Fifty-one (61.4%) of 83 Salmonella enterica were typhoidal, while 32 (38.6%) were not. Sixty-five (78.3%) of the 83 Salmonella enterica isolates were resistant to ampicillin and trimethoprim-sulfamethoxazole, followed by chloramphenicol 39 (46.7%), tetracycline 41 (41.4%), piperacillin 33 (33.9%), amoxicillin-clavulanate, and streptomycin 21 (25.3%), while cephalothin was 19 (22.9%). Thirty-nine (46.9%) of the 83 Salmonella enterica isolates were multi-drug resistant, and none were extensive drug resistant or pan-drug resistant. A bla_TEM 42 (50.6%), floR 32 (38.6%), qnrA 24 (28.9%), tetB 20 (20.1%), tetA 10 (10.0%), and tetG 5 (6.0%) were the antibiotic resistance genes detected. There were perfect agreement between phenotypic and genotypic detection of antimicrobial resistance in tetracycline, ciprofloxacin, and chloramphenicol, while beta-lactam showed κ = 0.60 agreement. All of the Salmonella enterica isolates had the virulence genes invA, sopB, mgtC, and sip4D, while 33 (39.8%), 45 (51.8%), and 2 (2.4%) had ssaQ, spvC, and ljsGI-1, respectively.

Conclusion

Our findings showed multi-drug resistant Salmonella enterica in children with bacteremia in northern Nigeria. In addition, significant virulence and antimicrobial resistance genes were found in invasive Salmonella enterica in northern Nigeria. Thus, our study emphasizes the need to monitor antimicrobial resistance in Salmonella enterica from invasive sources in Nigeria and supports antibiotic prudence.

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.

Development and Characterization of a Luminescence-Based High-Throughput Serum Bactericidal Assay (L-SBA) to Assess Bactericidal Activity of Human Sera against Nontyphoidal Salmonella

Salmonella Typhimurium and Salmonella Enteritidis are leading causative agents of invasive nontyphoidal Salmonella (iNTS) disease, which represents one of the major causes of death and morbidity in sub-Saharan Africa, still partially underestimated. Large sero-epidemiological studies are necessary to unravel the burden of disease and guide the introduction of vaccines that are not yet available. Even if no correlate of protection has been determined so far for iNTS, the evaluation of complement-mediated functionality of antibodies generated towards natural infection or elicited upon vaccination may represent a big step towards this achievement. Here we present the setup and the intra-laboratory characterization in terms of repeatability, intermediate precision, linearity, and specificity of a high-throughput luminescence-based serum bactericidal assay (L-SBA). This method could be useful to perform sero-epidemiological studies across iNTS endemic countries and for evaluation of antibodies raised against iNTS vaccine candidates in upcoming clinical trials.

Molecular diagnostics and next-generation sequencing reveal real etiological characteristics of invasive Salmonella infection in febrile illness in Freetown, Sierra Leone

Invasive Salmonella infection, which can cause typhoid/paratyphoid fever and invasive non-typhoidal salmonellosis, is a public health burden in Africa. Accurate diagnosis and etiological characterization are required to conduct prevalence and risk estimations for Salmonella infection; however, the utilization of optimal techniques and surveillance data are still insufficient. In this study, we performed a laboratory-based survey in Freetown, which is the biggest city in Sierra Leone with a high burden of typhoid fever, by using blood culture and molecular methods but not the Widal test, to estimate the prevalence and aetiology of invasive Salmonella infection among fever patients. We found a very low prevalence of typhoid fever in patients with fever during the investigation period, and this prevalence was clearly overestimated by the Widal test. Genome sequencing of the S. Typhi isolate from this work revealed that the strain carried multiple antibiotic resistance genes, and an epidemic clone that has existed in West Africa for years was also detected in Sierra Leone. By using metagenomic sequencing, one patient with invasive non-typhoidal salmonellosis was identified as having bacterial co-infections. Our data highlight that Salmonella surveillance based on accurate laboratory diagnosis and genome sequencing needs to be strengthened to provide a better estimation of the real epidemics and enable potential risk assessment by etiological analysis in Africa. Even in a laboratory with only basic equipment, it is possible to conduct next-generation sequencing for pathogen discovery in bloodstream infections and to determine the etiological characteristics of pathogene without complex combinations of laboratory methods.

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 characterization of Salmonella Infantis from South Africa, 2004-2016

Salmonella Infantis is presenting an increasing risk to public health. Of particular concern are the reports of pESI, a multidrug resistance (MDR) encoding megaplasmid, in isolates from multiple countries, but little is known about its presence or diversity in South Africa. Whole genome sequences of 387 S. Infantis isolates from South Africa (2004-2020) were analysed for genetic phylogeny, recombination frequency, antimicrobial resistance (AMR) determinants, plasmid presence and overall gene content. The population structure of South African S. Infantis was substantially different to S. Infantis reported elsewhere; only two thirds of isolates belonged to eBG31, while the remainder were identified as eBG297, a much rarer group globally. Significantly higher levels of recombination were observed in the eBG297 isolates, which was associated with the presence of prophages. The majority of isolates were putatively susceptible to antimicrobials (335/387) and lacked any plasmids (311/387); the megaplasmid pESI was present in just one isolate. A larger proportion of eBG31 isolates, 19% (49/263), contained at least one AMR determinant, compared to eBG297 at 2% (3/124). Comparison of the pan-genomes of isolates from either eBG identified 943 genes significantly associated with eBG, with 43 found exclusively in eBG31 isolates and 34 in eBG297 isolates. This, along with the single nucleotide polymorphism distance and difference in resistance profiles, suggests that eBG31 and eBG297 isolates occupy different niches within South Africa. If antibiotic-resistant S. Infantis emerges in South Africa, probably through the spread of the pESI plasmid, treatment of this infection would be compromised.

Paratyphoid Fever A: Infection and Prevention

Enteric fever is caused by Salmonella enterica serovar Typhi, Salmonella enterica serovar Paratyphi A, B, and C. While S. Typhi remains the primary causative agent of enteric fever, S. Paratyphi A is responsible for an increasing portion of enteric fever incidence. However, the current available vaccines for enteric fever are all developed from S. Typhi, and lack adequate cross immune protection against paratyphoid fever A. Therefore, paratyphoid A vaccines are urgently needed. The present paper reviews the latest progresses in pathogenesis, global burden, infection features of paratyphoid fever A, as well as the status of vaccine development, highlighting the necessity for the development of vaccines against paratyphoid fever A.

Can Nanobubble Ozone Liposomes Be A New Agent In The Fight Against Foodborne Infections?

Backrounds: In our study, a nanoparticle liposome molecule with patent application number TR2021004032 was used, and the Minimum Inhibitor Concentration (MIC) was found to be 1562 ppm. According to the ASTM F 1980 standard, it has been determined that the nanoparticle liposome solution kept at 37 days and 55 oC in return for one-year stability preserves its effectiveness. Our study aimed to show that the newly developed solution maintains its effectiveness for a long time.

METHODS

In this study, a nanobubble ozone liposome solution containing 2% ZnCl2 was used. The aging tests were conducted according to the ASTM F 1980 [1] standards. The minimum inhibitory concentration (MIC) level of the nanobubble ozone liposome solution with 2% ZnCl2 was determined as 1.562 ppm for strains of Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) by the CLSI M07 A9 [2] standard test method. To assess the time-dependent antibacterial effect of the nanobubble liposome solution with 2% ZnCl2, the solution's efficiency at a concentration of 2000 ppm and for different time intervals was tested on strains of Salmonella enterica subsp. enterica (ATCC® 14028™) and Listeria monocytogenes (ATCC® 7644™).

RESULTS

The results showed that the antibacterial activity of the strains of S. enterica subsp. enterica started at the end of the 10th minute and the solution was effective after 30 minutes. For strains of L. monocytogenes, it was observed that the activity started at the end of the 2nd minute and the product was effective after the 10th minute. According to the ASTM F 1980 standards, it was found that the nanobubble ozone liposome solution retained its effectiveness in one-year stability tests.

CONCLUSION

As a result, the nanoparticle liposome solution, a new product, does not lose its stability and effectiveness for a long time, contrary to what is known. Although the half-life of gaseous ozone is as short as 20 minutes, the stability in the nanoparticle liposome solution has been determined as at least one year. Since nanoparticle liposome solution is a natural and slow-release product, nanobubble ozone liposome solution with 2% ZnCl2 may be used as a newly developed agent against contaminations in food processing facilities caused by biofilm-forming microorganisms through the use in disinfections of surfaces that are in direct contact with food products.

Inflammatory Monocytes Promote Granuloma-Mediated Control of Persistent Salmonella Infection

Persistent infections generally involve a complex balance between protective immunity and immunopathology. We used a murine model to investigate the role of inflammatory monocytes in immunity and host defense against persistent salmonellosis. Mice exhibit increased susceptibility to persistent infection when inflammatory monocytes cannot be recruited into tissues or when they are depleted at specific stages of persistent infection. Inflammatory monocytes contribute to the pathology of persistent salmonellosis and cluster with other cells in pathogen-containing granulomas. Depletion of inflammatory monocytes during the chronic phase of persistent salmonellosis causes regression of already established granulomas with resultant pathogen growth and spread in tissues. Thus, inflammatory monocytes promote granuloma-mediated control of persistent salmonellosis and may be key to uncovering new therapies for granulomatous diseases.

Non-typhoidal Salmonella infections across India: emergence of a neglected group of enteric pathogens

Objective

Non-typhoidal Salmonellae (NTS) are a neglected group of enteric pathogens whose prevalence is increasing at alarming rates across India. The disease burden is being underestimated because of a lack of effective surveillance of NTS infections in the Indian population. This study depicts the acquisition of NTS infection, and its persistence and spread through a diverse range of hosts, including humans and animals, and food and environmental sources.

Methods

During the study period from 2016 to 2018, a total of 999 suspected NTS isolates were received from across India and were phenotypically and serologically characterized for the presence of NTS.

Results

Of the 999 isolates, 539 (53.95%) were confirmed as NTS, consisting of 17 different NTS serovars. The majority were isolated from human samples (n = 319, 59.18%), followed by food products (n = 99, 18.37%), animals (n = 83, 15.4%) and the environment (n = 38, 7.05%). Some predominant serovars obtained included S. Typhimurium (n = 167, 30.98%), S. Lindenberg (n = 135, 25.05%), S. Enteritidis (n = 56, 10.39%), S. Weltevreden (n = 44, 8.16%), S. Choleraesuis (n = 41, 7.61%) and S. Mathura (n = 33, 6.12%).

Conclusion

This study depicts the NTS disease burden across India, on the basis of the isolation of NTS serovars across diverse geographic locations. The emergence of newer or less common NTS serovars implicated in human infection poses a potential challenge to the healthcare system in India. Therefore, national and regional level surveillance is needed to implement effective control strategies and safeguard community health in India.

Genomic diversity and antimicrobial resistance among non-typhoidal Salmonella associated with human disease in The Gambia

Non-typhoidal Salmonella associated with multidrug resistance cause invasive disease in sub-Saharan Africa. Specific lineages of serovars Typhimurium and Enteritidis have been implicated. Here we characterized the genomic diversity of 100 clinical non-typhoidal Salmonella collected from 93 patients in 2001 from the eastern, and in 2006-2018 from the western regions of The Gambia respectively. A total of 93 isolates (64 invasive, 23 gastroenteritis and six other sites) representing a single infection episode were phenotypically tested for antimicrobial susceptibility using the Kirby-Bauer disc diffusion technique. Whole genome sequencing of 100 isolates was performed using Illumina, and the reads were assembled and analysed using SPAdes. The Salmonella in Silico Typing Resource (SISTR) was used for serotyping. SNP differences among the 93 isolates were determined using Roary, and phylogenetic analysis was performed in the context of 495 African strains from the European Nucleotide Archive. Salmonella serovars Typhimurium (26/64; 30.6 %) and Enteritidis (13/64; 20.3 %) were associated with invasive disease, whilst other serovars were mainly responsible for gastroenteritis (17/23; 73.9 %). The presence of three major serovar Enteritidis clades was confirmed, including the invasive West African clade, which made up more than half (11/16; 68.8 %) of the genomes. Multidrug resistance was confined among the serovar Enteritidis West African clade. The presence of this epidemic virulent clade has potential for spread of resistance and thus important implications for systematic patient management. Surveillance and epidemiological investigations to inform control are warranted.

The Impact of Overstocking and Negative Energy Balance on Quantitative Measurement of Non-typhoidal Salmonella in Periparturient Dairy Cattle

Stressful conditions in animal production facilities may exacerbate the fecal shedding and foodborne transmission of non-typhoidal Salmonella enterica subsp. enterica. Dairy cows are reservoirs of this zoonotic microorganism, and its prevalence has roughly doubled in the past decade on dairy farms in United States. Dairy cows are commonly overstocked at the feed bunk, and stressors placed on the animal prior to parturition may exacerbate Salmonella shedding. However, no studies have evaluated the impact of overstocking and metabolic stress on fecal concentrations of the pathogen. Therefore, we conducted a field trial with 120 multiparous dairy cows randomized into one of four treatment groups with different stocking densities at the feed bunk during the periparturient period as follows: US, understocked from −60 to −1 DRC; OS, overstocked from −60 to −1 DRC; USOS, understocked from −60 to −26 DRC/overstocked from −25 to −1 DRC; and OSUS, overstocked from −60 to −26 DRC/ understocked from −25 to −1 DRC. Fecal and blood samples were collected at four time points relative to calving. qPCR assays were used to quantify Salmonella invA gene and total bacterial community from fecal samples, and a subset of isolates recovered from fecal bacterial culture were characterized using pulsed field gel electrophoresis and serotyping. Serum non-esterified fatty acids (NEFA) were measured as a metabolic stress indicator using an immunoassay. Multivariable analyses were performed to test if changes in Salmonella concentrations were associated with stocking density, energy balance, or days relative to calving. From fecal isolates, three Salmonella serovars were identified, S. Cerro; Kentucky; Meleagridis. Concentrations of Salmonella increased as cows approached calving. Higher stocking densities at the feed bunk did not impact total bacterial community or NEFA; however, cows in the overstocked groups had higher Salmonella fecal concentrations. Further, cows with higher NEFA concentrations after calving had a higher likelihood of detection of Salmonella. Future farm interventions should aim to reduce environmental and metabolic stress during the periparturient period to decrease the dissemination of Salmonella to cattle, the environment, and humans.

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.

Prevalence, probability, and outcomes of typhoidal/non-typhoidal Salmonella and malaria co-infection among febrile patients: a systematic review and meta-analysis

The geographical overlaps of malaria parasites and Salmonella spp. can lead to co-infection of these two pathogens, especially in the tropics where malaria is endemic. Moreover, few literatures suggested that malaria infection was associated with Salmonella bacteremia. Therefore, this study quantified pooled prevalence of typhoidal/non-typhoidal Salmonella (NTS) and probability of typhoidal/NTS and malaria co-infection among febrile patients. The systematic review protocol was registered at PROSPERO (CRD42021252322). Studies on co-infection of typhoidal/NTS and malaria were searched in PubMed, Scopus, and Web of Science. The risk of bias of the included studies was assessed using the checklist for analytical cross-sectional studies developed by the Joanna Briggs Institute. Meta-analyses on the following criteria were performed: (1) pooled prevalence of typhoidal/NTS and malaria co-infection among febrile patients, (2) pooled prevalence of typhoidal/NTS among malaria patients, (3) pooled prevalence of malaria infections among patients with Salmonella spp. infection, and (4) probability of typhoidal/NTS and malaria co-infection among febrile patients. Additionally, the case fatality rate and mean difference of malarial parasitemia between typhoidal/NTS and malaria co-infection and Plasmodium monoinfection were also determined. The subgroup analyses of typhoidal/NTS, regions (Africa and Asia), countries, time (publication year), characteristics of participants, and diagnostic tests for identifying Salmonella spp. were also conducted. A sensitivity test was performed to determine the robustness of the study outcomes. Publication bias among the included studies was evaluated using the funnel plot and Egger’s test. All analyses were performed using Stata version 15 (StataCorp LLC, Texas, USA) with a p-value < 0.05 indicating statistical significance. Eighty-one studies that met the eligibility criteria were included in the analyses. Of the 73,775 study participants, 4523 had typhoidal/NTS and malaria co-infections. The pooled prevalence rates of typhoidal/NTS and malaria co-infection among febrile patients were 14% (95% confidence interval [CI], 9–19%; I², 99.4%; 2971/17,720 cases) and 1% (95% CI 1–1%; I², 89.9%; 252/29,081 cases) using the Widal test and culture methods for identifying Salmonella spp., respectively. The pooled prevalence rates of typhoidal/NTS infection among patients with malaria were 31% (95% CI 23–39%; I², 99.5%; 3202/19,208 cases) and 3% (95% CI 2–3%; I², 86.8%; 407/40,426 cases) using the Widal test and culture methods for identifying Salmonella spp., respectively. The pooled prevalence rates of malaria infection among patients with typhoidal/NTS were 17% (95% CI 6–29%; I², 33.3%; 13/75 cases) and 43% (95% CI 32–53%; I², 89.1%; 287/736 cases), respectively. Malaria infection was associated with typhoidal/NTS in children aged < 15 years (p < 0.0001; odds ratio, 0.36; 95% CI 0.23–0.58; I², 73.9%; 3188/43,212 cases). The case fatality rate in patients with malaria and NTS co-infections was 16% (95% CI 9–24%; I², 89.1%; 18/103 cases). From the view of the present study, the inappropriate use of the Widal test for Salmonella spp. diagnosis can overestimate the prevalence of typhoidal/NTS and malaria co-infections. Malaria infection associated with typhoidal/NTS in children and the high case fatality rates among few patients with co-infections were highlighted. Future prospective longitudinal studies using the appropriate and confirmatory dsiagnosis for Salmonella spp. infections are highly recommended to ensure the real prevalence of co-infection and highlight the outcome of co-infection for providing adequate treatment in febrile patients who live in areas where malaria is endemic, such as tropical Africa and India.

Invasive atypical non-typhoidal Salmonella serovars in The Gambia

Invasive non-typhoidal Salmonella (iNTS) disease continues to be a significant public health problem in sub-Saharan Africa. Common clinical misdiagnosis, antimicrobial resistance, high case fatality and lack of a vaccine make iNTS a priority for global health research. Using whole genome sequence analysis of 164 invasive Salmonella isolates obtained through population-based surveillance between 2008 and 2016, we conducted genomic analysis of the serovars causing invasive Salmonella diseases in rural Gambia. The incidence of iNTS varied over time. The proportion of atypical serovars causing disease increased over time from 40 to 65 % compared to the typical serovars Enteritidis and Typhimurium that decreased from 30 to 12 %. Overall iNTS case fatality was 10%, but case fatality associated with atypical iNTS alone was 10 %. Genetic virulence factors were identified in 14/70 (20 %) typical serovars and 45/68 (66 %) of the atypical serovars and were associated with: invasion, proliferation and/or translocation (Clade A); and host colonization and immune modulation (Clade G). Among Enteritidis isolates, 33/40 were resistant to four or more of the antimicrobials tested, except ciprofloxacin, to which all isolates were susceptible. Resistance was low in Typhimurium isolates, but all 16 isolates were resistant to gentamicin. The increase in incidence and proportion of iNTS disease caused by atypical serovars is concerning. The increased proportion of atypical serovars and the high associated case fatality may be related to acquisition of specific genetic virulence factors. These factors may provide a selective advantage to the atypical serovars. Investigations should be conducted elsewhere in Africa to identify potential changes in the distribution of iNTS serovars and the extent of these virulence elements.

Invasive salmonellosis in paediatric patients in the Northern Territory, Australia, 2005-2015

AIM

To describe the epidemiology of invasive Salmonella disease in children in the Northern Territory, Australia.

METHODS

Design: A retrospective review of invasive salmonellosis cases identified by pathology records and the Northern Territory Notifiable Disease Surveillance System. Case definitions: Those aged 18 years or under, with Salmonella cultured from a usually sterile site, collected in the Northern Territory between 1 July 2005 and 30 June 2015.

OUTCOME MEASURES

The primary outcome measure was the annual incidence rate of invasive salmonellosis, comparing rates between Indigenous and non-Indigenous children.

RESULTS

There were 86 cases of invasive Salmonella infection in children over the 10-year period; an annual incidence of 14.1 per 100 000 population, in those aged less than 18 years. Gastrointestinal Salmonella notifications were similar between Indigenous and non-Indigenous children. In children aged less than 15 years, the rate of invasive salmonellosis was higher in Indigenous children compared to non-Indigenous children (23.4 per 100 000 compared with 11.6 per 100 000); rate ratio 2.0 (95% confidence interval 1.3-3.3, P = 0.002). Indigenous children with invasive salmonellosis had a median hospital stay of 8 days, which was compared to 5 days for non-Indigenous children (P = 0.015). The highest incidence rate of invasive salmonellosis occurred in Indigenous patients less than 12 months of age (138 per 100 000).

CONCLUSION

The Northern Territory of Australia has high rates of invasive salmonellosis in children. Indigenous and non-Indigenous children experience similar rates of Salmonella gastroenteritis but Indigenous children experience higher rates of invasive salmonellosis.

The genomic epidemiology of multi-drug resistant invasive non-typhoidal Salmonella in selected sub-Saharan African countries

Background

Invasive non-typhoidal Salmonella (iNTS) is one of the leading causes of bacteraemia in sub-Saharan Africa. We aimed to provide a better understanding of the genetic characteristics and transmission patterns associated with multi-drug resistant (MDR) iNTS serovars across the continent.

Methods

A total of 166 iNTS isolates collected from a multi-centre surveillance in 10 African countries (2010–2014) and a fever study in Ghana (2007–2009) were genome sequenced to investigate the geographical distribution, antimicrobial genetic determinants and population structure of iNTS serotypes–genotypes. Phylogenetic analyses were conducted in the context of the existing genomic frameworks for various iNTS serovars. Population-based incidence of MDR-iNTS disease was estimated in each study site.

Results

Salmonella Typhimurium sequence-type (ST) 313 and Salmonella Enteritidis ST11 were predominant, and both exhibited high frequencies of MDR; Salmonella Dublin ST10 was identified in West Africa only. Mutations in the gyrA gene (fluoroquinolone resistance) were identified in S. Enteritidis and S. Typhimurium in Ghana; an ST313 isolate carrying bla_CTX-M-15 was found in Kenya. International transmission of MDR ST313 (lineage II) and MDR ST11 (West African clade) was observed between Ghana and neighbouring West African countries. The incidence of MDR-iNTS disease exceeded 100/100 000 person-years-of-observation in children aged <5 years in several West African countries.

Conclusions

We identified the circulation of multiple MDR iNTS serovar STs in the sampled sub-Saharan African countries. Investment in the development and deployment of iNTS vaccines coupled with intensified antimicrobial resistance surveillance are essential to limit the impact of these pathogens in Africa.

Microbiological and genomic investigations of invasive Salmonella enterica serovar Panama from a large outbreak in Taiwan

BACKGROUND/PURPOSE

Salmonella Panama was considered an invasive non-typhoidal Salmonella (iNTS) serovar. Comprehensive clinical, microbiological, and genomic studies on S. Panama are scarce. We aimed to characterize the clinical and microbiological characteristics of S. Panama infection. Virulence mechanism of S. Panama and other iNTS serovars were also examined.

METHODS

Based on data from the longitudinal surveillance system for Salmonella deployed in Taiwan since 2004, a case-control study was undertaken to evaluate clinical characteristics of S. Panama infection during an outbreak in 2015-2016. Cellular experiments were conducted to compare pathogenicity of S. Panama and other iNTS with S. Typhimurium.

RESULTS

Most patients (41/44, 93.2%) infected by S. Panama were <5 years old (median, 1.3 years). The case-control study showed that 28 out of the 41 (68.3%) manifested as bacteremia, compared to S. Typhimurium (11.1%). Patients infected by S. Panama had longer durations of fever (P = 0.005) and hospitalization (P < 0.001). Genomic analyses split the isolates into three clades: two clones caused the outbreak, whereas another one accounted for the sporadic infections before 2015. Cellular experiments revealed that S. Panama and other iNTS serovars showed higher monolayer penetration and intracellular survival within macrophages, compared to S. Typhimurium.

CONCLUSION

This study confirmed that S. Panama is a clinically invasive serovar. Different iNTS serovars express common virulence phenotypes, but they may acquire invasiveness through distinct expression or combinations of virulence genes.

Long-Term Anti-Bacterial Immunity against Systemic Infection by Salmonella enterica Serovar Typhimurium Elicited by a GMMA-Based Vaccine

Salmonella Typhimurium (STm) represents the most prevalent cause of invasive non-typhoidal Salmonella (iNTS) disease, and currently no licensed vaccine is available. In this work we characterized the long-term anti-bacterial immunity elicited by a STm vaccine based on Generalized Modules of Membrane Antigens (GMMA) delivering O:4,5 antigen, using a murine model of systemic infection. Subcutaneous immunization of mice with STmGMMA/Alhydrogel elicited rapid, high, and persistent antigen-specific serum IgG and IgM responses. The serum was bactericidal in vitro. O:4,5-specific IgG were also detected in fecal samples after immunization and positively correlated with IgG observed in intestinal washes. Long-lived plasma cells and O:4,5-specific memory B cells were detected in spleen and bone marrow. After systemic STm challenge, a significant reduction of bacterial load in blood, spleen, and liver, as well as a reduction of circulating neutrophils and G-CSF glycoprotein was observed in STmGMMA/Alhydrogel immunized mice compared to untreated animals. Taken together, these data support the development of a GMMA-based vaccine for prevention of iNTS disease.

Classification of Salmonella enterica of the (Para-)Typhoid Fever Group by Fourier-Transform Infrared (FTIR) Spectroscopy

Typhoidal and para-typhoidal Salmonella are major causes of bacteraemia in resource-limited countries. Diagnostic alternatives to laborious and resource-demanding serotyping are essential. Fourier transform infrared spectroscopy (FTIRS) is a rapidly developing and simple bacterial typing technology. In this study, we assessed the discriminatory power of the FTIRS-based IR Biotyper (Bruker Daltonik GmbH, Bremen, Germany), for the rapid and reliable identification of biochemically confirmed typhoid and paratyphoid fever-associated Salmonella isolates. In total, 359 isolates, comprising 30 S. Typhi, 23 S. Paratyphi A, 23 S. Paratyphi B, and 7 S. Paratyphi C, respectively and other phylogenetically closely related Salmonella serovars belonging to the serogroups O:2, O:4, O:7 and O:9 were tested. The strains were derived from clinical, environmental and food samples collected at different European sites. Applying artificial neural networks, specific automated classifiers were built to discriminate typhoidal serovars from non-typhoidal serovars within each of the four serogroups. The accuracy of the classifiers was 99.9%, 87.0%, 99.5% and 99.0% for Salmonella Typhi, Salmonella Paratyphi A, B and Salmonella Paratyphi C, respectively. The IR Biotyper is a promising tool for fast and reliable detection of typhoidal Salmonella. Hence, IR biotyping may serve as a suitable alternative to conventional approaches for surveillance and diagnostic purposes.

Antivirulence DsbA inhibitors attenuate Salmonella enterica serovar Typhimurium fitness without detectable resistance

Inhibition of the DiSulfide Bond (DSB) oxidative protein folding machinery, a major facilitator of virulence in Gram‐negative bacteria, represents a promising antivirulence strategy. We previously developed small molecule inhibitors of DsbA from Escherichia coli K‐12 (EcDsbA) and showed that they attenuate virulence of Gram‐negative pathogens by directly inhibiting multiple diverse DsbA homologues. Here we tested the evolutionary robustness of DsbA inhibitors as antivirulence antimicrobials against Salmonella enterica serovar Typhimurium under pathophysiological conditions in vitro. We show that phenylthiophene DsbA inhibitors slow S. Typhimurium growth in minimal media, phenocopying S. Typhimurium isogenic dsbA null mutants. Through passaging experiments, we found that DsbA inhibitor resistance was not induced under conditions that rapidly induced resistance to ciprofloxacin, an antibiotic commonly used to treat Salmonella infections. Furthermore, no mutations were identified in the dsbA gene of inhibitor‐treated S. Typhimurium, and S. Typhimurium virulence remained susceptible to DsbA inhibitors. Our work demonstrates that under in vitro pathophysiological conditions, DsbA inhibitors can have both antivirulence and antibiotic action. Importantly, our finding that DsbA inhibitors appear to be evolutionarily robust offers promise for their further development as next‐generation antimicrobials against Gram‐negative pathogens.

Staged progression epidemic models for the transmission of invasive nontyphoidal Salmonella (iNTS) with treatment

We develop and analyze a stage-progression compartmental model to study the emerging invasive nontyphoidal Salmonella (iNTS) epidemic in sub-Saharan Africa. iNTS bloodstream infections are often fatal, and the diverse and non-specific clinical features of iNTS make it difficult to diagnose. We focus our study on identifying approaches that can reduce the incidence of new infections. In sub-Saharan Africa, transmission and mortality are correlated with the ongoing HIV epidemic and severe malnutrition. We use our model to quantify the impact that increasing antiretroviral therapy (ART) for HIV infected adults and reducing malnutrition in children would have on mortality from iNTS in the population. We consider immunocompromised subpopulations in the region with major risk factors for mortality, such as malaria and malnutrition among children and HIV infection and ART coverage in both children and adults. We parameterize the progression rates between infection stages using the branching probabilities and estimated time spent at each stage. We interpret the basic reproduction number R0 as the total contribution from an infinite infection loop produced by the asymptomatic carriers in the infection chain. The results indicate that the asymptomatic HIV+ adults without ART serve as the driving force of infection for the iNTS epidemic. We conclude that the worst disease outcome is among the pediatric population, which has the highest infection rates and death counts. Our sensitivity analysis indicates that the most effective strategies to reduce iNTS mortality in the studied population are to improve the ART coverage among high-risk HIV+ adults and reduce malnutrition among children.

Non-traumatic rupture of voluminous non-typhoid Salmonella splenic abscess presenting with peritonitis: Case report and review of the literature

•

Splenic abscess (SA) is an uncommon and life-threatening disease.

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Spontaneous rupture of a SA with peritonitis is a rare occurrence.

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Preoperative diagnosis of ruptured SA is a challenge due to non-specific clinical presentation.

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Nowadays there are no guidelines for the management of SA.

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Splenectomy represents the treatment of choice along with antibiotics in ruptured SA.

Introduction and importance

Splenic abscess (SA) is an uncommon, life-threatening disease with about 600 reported cases in the literature. It is caused by various infective pathogens and generally occurs in immunocompromised patients. SA is a rare complication of non-typhoid Salmonella (NTS) infection. Diagnosis of ruptured SA is a challenge because the absence of specific symptoms and signs. Abdominal computed tomography (CT) scan represents the gold standard in diagnosing of SA. Splenectomy is the treatment of choice of ruptured SA with peritonitis.

Case presentation

A 26-year-old Caucasian female was admitted to the Emergency Department with a three-day history of abdominal pain and fever. Physical examination revealed severe and generalized abdominal pain on superficial and deep palpation with obvious muscle guarding and rebound tenderness. Abdominal CT scan showed ruptured SA. Laboratory tests reported anemia (hemoglobin 10.4 g/dl). The patient was taken emergently to the operating room for splenectomy. The postoperative course was uneventful, the patient was discharged on the 7th post-operative day. Diagnosis of NTS SA was made by pus cultures.

Clinical discussion

SA is a rare complication of NTS infection associated with high morbidity and mortality rates. Although different types of treatment of SA are reported in the literature, splenectomy represents the treatment of choice of ruptured SA.

Conclusion

NTS SA is difficult to diagnose because of its rarity and non-specific clinical presentation, often fatal if left untreated. Although there is no gold standard for treating SA, splenectomy with peritoneal lavage is mandatory in case of ruptured SA with peritonitis.

Attenuated Salmonella enterica Serovar Typhimurium, Strain NC983, Is Immunogenic, and Protective against Virulent Typhimurium Challenges in Mice

Non-typhoidal Salmonella (NTS) serovars are significant health burden worldwide. Although much effort has been devoted to developing typhoid-based vaccines for humans, currently there is no NTS vaccine available. Presented here is the efficacy of a live attenuated serovar Typhimurium strain (NC983). Oral delivery of strain NC983 was capable of fully protecting C57BL/6 and BALB/c mice against challenge with virulent Typhimurium. Strain NC983 was found to elicit an anti-Typhimurium IgG response following administration of vaccine and boosting doses. Furthermore, in competition experiments with virulent S. Typhimurium (ATCC 14028), NC983 was highly defective in colonization of the murine liver and spleen. Collectively, these results indicate that strain NC983 is a potential live attenuated vaccine strain that warrants further development.

Antibodies and Protection in Systemic Salmonella Infections: Do We Still Have More Questions than Answers?

Salmonella causes grave systemic infections in humans and other animals and provides a paradigm for other diseases in which the bacteria have both intracellular and extracellular lifestyles. New generations of vaccines rely on the essential contribution of the antibody responses for their protection. The quality, antigen specificity, and functions associated with antibody responses to this pathogen have been elusive for a long time. Recent approaches that combine studies in humans and genetically manipulated experimental models and that exploit awareness of the location and within-host life cycle of the pathogen are shedding light on how humoral immunity to Salmonella operates. However, this area of research remains full of controversy and discrepancies. The overall scenario indicates that antibodies are essential for resistance against systemic Salmonella infections and can express the highest protective function when operating in conjunction with cell-mediated immunity. Antigen specificity, isotype profile, Fc-gamma receptor usage, and complement activation are all intertwined factors that still arcanely influence antibody-mediated protection to Salmonella.

High relatedness of invasive multi-drug resistant non-typhoidal Salmonella genotypes among patients and asymptomatic carriers in endemic informal settlements in Kenya

Invasive Non-typhoidal Salmonella (iNTS) disease is a major public health challenge, especially in Sub-Saharan Africa (SSA). In Kenya, mortality rates are high (20-25%) unless prompt treatment is instituted. The most common serotypes are Salmonella enterica serotype Typhimurium (S. Typhimurium) and Salmonella enterica serotype Enteritidis (S. Enteritidis). In a 5 year case-control study in children residing in the Mukuru informal settlement in Nairobi, Kenya, a total of 4201 blood cultures from suspected iNTS cases and 6326 fecal samples from age-matched controls were studied. From the laboratory cultures we obtained a total of 133 S. Typhimurium isolates of which 83(62.4%) came from cases (53 blood and 30 fecal) and 50(37.6%) from controls (fecal). A total of 120 S. Enteritidis consisted of 70(58.3%) from cases (43 blood and 27 fecal) and 50(41.7%) from controls (fecal). The S. Typhimurium population fell into two distinct ST19 lineages constituting 36.1%, as well as ST313 lineage I (27.8%) and ST313 lineage II (36.1%) isolates. The S. Enteritidis isolates fell into the global epidemic lineage (46.6%), the Central/Eastern African lineage (30.5%), a novel Kenyan-specific lineage (12.2%) and a phylogenetically outlier lineage (10.7%). Detailed phylogenetic analysis revealed a high level of relatedness between NTS from blood and stool originating from cases and controls, indicating a common source pool. Multidrug resistance was common throughout, with 8.5% of such isolates resistant to extended spectrum beta lactams. The high rate of asymptomatic carriage in the population is a concern for transmission to vulnerable individuals and this group could be targeted for vaccination if an iNTS vaccine becomes available.

Highly antimicrobial-resistant Nontyphoidal Salmonella from retail meats and clinical impact in children, Taiwan

BACKGROUND

The epidemiology of nontyphoidal Salmonella (NTS) resistant to ciprofloxacin or ceftriaxone and its impact on patients' clinical course are rarely reported.

METHODS

Children with culture-proven salmonellosis treated in a medical center in northern Taiwan in 2017 were enrolled. To trace the source of Salmonella, Salmonella isolated from food samples were collected from markets. Antimicrobial susceptibility and serotypes were determined.

RESULTS

Among the 453 isolates, 122 (26.9%) were highly antimicrobial-resistant, as defined by resistance to ciprofloxacin or ceftriaxone or both. The most prevalent highly resistant serotype was S. Anatum (66, 54.1%). Salmonella was detected in 94.1%, 66.7%, and 8.6% of examined pork, chicken, and vegetables examined, respectively. S. Anatum (6, 21.4%) and S. Derby (6, 21.4%) were the major serotypes isolated. Majority of the S. Anatum (5, 83.3%) were highly antimicrobial-resistant. More patients infected by highly resistant Salmonella required carbapenem treatment (OR = 23.5, 95% confidence interval [CI] 2.8-192.7, P < 0.001). Patients with ceftriaxone-resistant NTS infections had a significantly longer hospital stay than others (P < 0.001). Totally, 34 (7.5%) presented with invasive diseases (31 bacteremia, 1 intestinal perforation, 1 toxic megacolon and 1 septic arthritis). Risk factors for invasive disease included prolonged fever for ≧5 days and infection occurring in warmer season from May to October. The rise of ambient temperature in northern Taiwan was associated with increasing Salmonella infections.

CONCLUSIONS

Retail meats were the main source of highly antimicrobial-resistant NTS in northern Taiwan. Highly antimicrobial resistance significantly impacted the clinical course and treatment of children with NTS infection.

Within-host spatiotemporal dynamic of systemic salmonellosis: Ways to track infection, reaction to vaccination and antimicrobial treatment

During the last two decades our understanding of the complex in vivo host-pathogen interactions has increased due to technical improvements and new research tools. The rapid advancement of molecular biology, flow cytometry and microscopy techniques, combined with mathematical modelling, have empowered in-depth studies of systemic bacterial infections across scales from single molecules, to cells, to organs and systems to reach the whole organism level. By tracking subpopulations of bacteria in vivo using molecular or fluorescent tags, it has been possible to reconstruct the spread of infection within and between organs, allowing unprecedented quantification of the effects of antimicrobial treatment and vaccination. This review illustrates recent advances in the study of heterogeneous traits of the infection process and illustrate approaches to investigate the reciprocal interactions between antimicrobial treatments, bacterial growth/death as well as inter- and intra-organ spread. We also discuss how vaccines impact the in vivo behaviour of bacteria and how these findings can guide vaccine design and rational antimicrobial treatment.

Pathogenic signature of invasive non-typhoidal Salmonella in Africa: implications for vaccine development

Invasive non-typhoidal Salmonella (iNTS) infections are a leading cause of bacteremia in Sub-Saharan Africa (sSA), thereby representing a major public health threat. Salmonella Typhimurium clade ST313 and Salmonella Enteriditis lineages associated with Western and Central/Eastern Africa are among the iNTS serovars which are of the greatest concern due to their case-fatality rate, especially in children and in the immunocompromised population. Identification of pathogen-associated features and host susceptibility factors that increase the risk for invasive non-typhoidal salmonellosis would be instrumental for the design of targeted prevention strategies, which are urgently needed given the increasing spread of multidrug-resistant iNTS in Africa. This review summarizes current knowledge of bacterial traits and host immune responses associated with iNTS infections in sSA, then discusses how this knowledge can guide vaccine development while providing a summary of vaccine candidates in preclinical and early clinical development.

The risk of infectious pathogens in breast-feeding, donated human milk and breast milk substitutes

OBJECTIVE

This review collates the published reports that focus on microbial and viral illnesses that can be transmitted by breast milk, donor milk and powdered infant formula (PIF). In this context, we attempt to define a risk framework encompassing those hazards, exposure scenarios, vulnerability and protective factors.

DESIGN

A literature search was performed for reported cases of morbidity and mortality associated with different infant feeding modes.

SETTING

Exclusive breast-feeding is the recommended for infant feeding under 6 months, or failing that, provision of donated human milk. However, the use of PIF remains high despite its intrinsic and extrinsic risk of microbial contamination, as well as the potential for adverse physiological effects, including infant gut dysbiosis.

RESULTS

Viable pathogen transmission via breast-feeding or donor milk (pasteurised and unpasteurised) is rare. However, transmission of HIV and human T-cell lymphotropic virus-1 is a concern for breast-feeding mothers, particularly for mothers undertaking a mixed feeding mode (PIF and breast-feeding). In PIF, intrinsic and extrinsic microbial contamination, such as Cronobacter and Salmonella, remain significant identifiable causes of infant morbidity and mortality.

CONCLUSIONS

Disease transmission through breast-feeding or donor human milk is rare, most likely owing to its complex intrinsically protective composition of human milk and protection of the infant gut lining. Contamination of PIF and the morbidity associated with this is likely underappreciated in terms of community risk. A better system of safe donor milk sharing that also establishes security of supply for non-hospitalised healthy infants in need of breast milk would reduce the reliance on PIF.

High Prevalence of Multidrug-Resistant and Extended-Spectrum β-Lactamase-Producing Enterobacteriaceae: A Cross-Sectional Study at Arsho Advanced Medical Laboratory, Addis Ababa, Ethiopia

Background

Multidrug-resistant Enterobacteriaceae particularly extended-spectrum beta-lactamase producers have become a major public health threat. Despite efforts to limit their spread, rates of multidrug-resistance members of the Enterobacteriaceae continue to increase throughout the world causing increased morbidity and mortality and raised costs for medical care.

Objective

The aim of this study was to determine the prevalence of multidrug resistance and extended-spectrum β-lactamase-producing Enterobacteriaceae.

Methods

Four hundred forty Enterobacteriaceae isolates from outpatients referred to Arsho Advanced Medical Laboratory were identified and assessed for their antimicrobial resistance pattern by using the automated VITEK 2 compact system. Extended-spectrum β-lactamase production was determined by the VITEK 2 automated compact system using the extended-spectrum β-lactamase test panel as per the instruction of the manufacturer.

Results

The overall resistance rates of Enterobacteriaceae against cephalosporins, aminoglycosides, and fluoroquinolones were high. Nitrofurantoin with a resistance rate of 14.3% and piperacillin/tazobactam combination with a resistance rate of 17.3% were better active against this group of Gram-negative bacteria. Out of 440 isolates of Enterobacteriaceae, 42.1% were multidrug-resistant of which 34.3% and 8.95% were extensively drug-resistant and pan-drug resistant, respectively. Among 185 multidrug-resistant Enterobacteriaceae, 63.9% of the isolates produced extended-spectrum β-lactamase of which 75.4%, 19.5%, 1.7%, 2.5%, and 0.8% were E. coli, K. pneumoniae, C. freundii, E. cloacae, and P. mirabilis, respectively.

Conclusions

The present study demonstrated high prevalence rates of multidrug-resistant and extended-spectrum-beta-lactamase-producing Enterobacteriaceae. In order to combat these problems, infection control strategy and proper antibiotic policies should be formulated.

Salmonella Contamination of Seafood in Landing Centers and Retail Markets of Mumbai, India

Background

Seafood contamination with Salmonella enterica is not only a public health concern, but can also lead to economic losses due to import rejections. Continuous monitoring of seafood for Salmonella is necessary for risk assessment and to establish suitable control measures.

Objective

The objective of this study was to determine the extent of Salmonella contamination of seafood in fish landing centers and retails markets.

Methods

In this study, we analyzed seafood samples from three fish landing centers and seven retail markets of Mumbai, India for S. enterica contamination. Salmonella was isolated using multiple selective enrichment broths and selective agars, and identified by conventional biochemical tests followed by polymerase chain reaction (PCR).

Results

Of 82 samples of seafood, comprising both finfish and shellfish, Salmonella was detected in 17 (20.7%) finfish samples. None of the shellfish samples (shrimps, clams, and cephalopods) were found to be contaminated with Salmonella. Samples from both landing centers and fish markets, as well as from pelagic and demersal sources, harbored Salmonella. Source-wise analysis showed that 11 of 57 (19.3%) samples from retail fish markets and 6 of 25 (24%) samples from fish landing centers were contaminated with Salmonella.

Conclusions

The study emphasizes the need to implement measures to prevent anthropogenic contamination of coastal waters and improve the hygiene of retail fish markets in Mumbai.

Highlights

Seafood from landing centers and retail markets, as well as from pelagic and demersalhabitats were similarly contaminated with Salmonella. Fish species widely consumed in the region of this study were found highly contaminated with Salmonella.

Extraintestinal Foodborne Pathogens

In general, foodborne diseases present themselves with gastrointestinal symptoms caused by bacterial, viral, and parasitic pathogens well established to be foodborne. These pathogens are also associated with extraintestinal clinical manifestations. Recent studies have suggested that Escherichia coli and Klebsiella pneumoniae, which both cause common extraintestinal infections such as urinary tract and bloodstream infections, may also be foodborne. The resolution and separation of these organisms into pathotypes versus commensals by modern genotyping methods have led to the identification of key lineages of these organisms causing outbreaks of extraintestinal infections. These epidemiologic observations suggested common- or point-source exposures, such as contaminated food. Here, we describe the spectrum of extraintestinal illnesses caused by recognized enteric pathogens and then review studies that demonstrate the potential role of extraintestinal pathogenic E. coli (ExPEC) and K. pneumoniae as foodborne pathogens. The impact of global food production and distribution systems on the possible foodborne spread of these pathogens is discussed.

Salmonella Virulence and Immune Escape

Salmonella genus represents the most common foodborne pathogens causing morbidity, mortality, and burden of disease in all regions of the world. The introduction of antimicrobial agents and Salmonella-specific phages has been considered as an effective intervention strategy to reduce Salmonella contamination. However, data from the United States, European countries, and low- and middle-income countries indicate that Salmonella cases are still a commonly encountered cause of bacterial foodborne diseases globally. The control programs have not been successful and even led to the emergence of some multidrug-resistant Salmonella strains. It is known that the host immune system is able to effectively prevent microbial invasion and eliminate microorganisms. However, Salmonella has evolved mechanisms of resisting host physical barriers and inhibiting subsequent activation of immune response through their virulence factors. There has been a high interest in understanding how Salmonella interacts with the host. Therefore, in the present review, we characterize the functions of Salmonella virulence genes and particularly focus on the mechanisms of immune escape in light of evidence from the emerging mainstream literature.

Humoral Immunity vs. Salmonella

In primary infection with Salmonella, it has been reported—without consideration of Salmonella's functions—that humoral immunity plays no role in the clearance of bacteria. In fact, Salmonella targets and suppresses several aspects of humoral immunity, including B cell lymphopoiesis, B cell activation, and IgG production. In particular, the suppression of IgG-secreting plasma cell maintenance allows the persistence of Salmonella in tissues. Therefore, the critical role(s) of humoral immunity in the response to Salmonella infection, especially at the late phase, should be re-investigated. The suppression of IgG plasma cell memory strongly hinders vaccine development against non-typhoidal Salmonella (NTS) because Salmonella can also reduce humoral immune memory against other bacteria and viruses, obtained from previous vaccination or infection. We propose a new vaccine against Salmonella that would not impair humoral immunity, and which could also be used as a treatment for antibody-dependent autoimmune diseases to deplete pathogenic long-lived plasma cells, by utilizing the Salmonella's own suppression mechanism of humoral immunity.

Evaluation of WGS-subtyping methods for epidemiological surveillance of foodborne salmonellosis

BACKGROUND

Salmonellosis is one of the most common foodborne diseases worldwide. Although human infection by non-typhoidal Salmonella (NTS) enterica subspecies enterica is associated primarily with a self-limiting diarrhoeal illness, invasive bacterial infections (such as septicaemia, bacteraemia and meningitis) were also reported. Human outbreaks of NTS were reported in several countries all over the world including developing as well as high-income countries. Conventional laboratory methods such as pulsed field gel electrophoresis (PFGE) do not display adequate discrimination and have their limitations in epidemiological surveillance. It is therefore very crucial to use accurate, reliable and highly discriminative subtyping methods for epidemiological characterisation and outbreak investigation.

METHODS

Here, we used different whole genome sequence (WGS)-based subtyping methods for retrospective investigation of two different outbreaks of Salmonella Typhimurium and Salmonella Dublin that occurred in 2013 in UK and Ireland respectively.

RESULTS

Single nucleotide polymorphism (SNP)-based cluster analysis of Salmonella Typhimurium genomes revealed well supported clades, that were concordant with epidemiologically defined outbreak and confirmed the source of outbreak is due to consumption of contaminated mayonnaise. SNP-analyses of Salmonella Dublin genomes confirmed the outbreak however the source of infection could not be determined. The core genome multilocus sequence typing (cgMLST) was discriminatory and separated the outbreak strains of Salmonella Dublin from the non-outbreak strains that were concordant with the epidemiological data however cgMLST could neither discriminate between the outbreak and non-outbreak strains of Salmonella Typhimurium nor confirm that contaminated mayonnaise is the source of infection, On the other hand, other WGS-based subtyping methods including multilocus sequence typing (MLST), ribosomal MLST (rMLST), whole genome MLST (wgMLST), clustered regularly interspaced short palindromic repeats (CRISPRs), prophage sequence profiling, antibiotic resistance profile and plasmid typing methods were less discriminatory and could not confirm the source of the outbreak.

CONCLUSIONS

Foodborne salmonellosis is an important concern for public health therefore, it is crucial to use accurate, reliable and highly discriminative subtyping methods for epidemiological surveillance and outbreak investigation. In this study, we showed that SNP-based analyses do not only have the ability to confirm the occurrence of the outbreak but also to provide definitive evidence of the source of the outbreak in real-time.

Molecular epidemiology and antimicrobial resistance of invasive non-typhoidal Salmonella in China, 2007-2016

Purpose

Human infections caused by invasive non-typhoidal Salmonella (iNTS) are highly prevalent worldwide. However, data for such infections in China are scarce. This study reports the epidemiology of iNTS in China.

Methods

INTS isolates were recovered from blood and other clinical specimens collected during 2007-2016 across five provinces (Shanghai, Xinjiang, Fujian, Guangxi, and Chongqing) in China. Antimicrobial susceptibility was performed using the agar dilution method and molecular epidemiology was performed using standard microbiological techniques.

Results

A total of 178 iNTS isolates were recovered from approximately 9700 patient specimens during 2007-2016. The predominant serovars were Salmonella Enteritidis (57/178, 32%), Salmonella Choleraesuis (47/178, 26.4%), and Salmonella Typhimurium (24/178, 13.5%). Up to 50 isolates (28.1%) were from patients who were ≤1 year of age, while 28 (15.7%) were from patients who were ≥60 years. Among these isolates, high rates of resistance to nalidixic acid (114/178, 64%), sulfisoxazole (59%), ciprofloxacin (15.2%), and cefotaxime (8.4%) were found. Moreover, 53.4% (95/178) exhibited multidrug resistance, and 3.9% (7/178) showed co-resistance to third-generation cephalosporins and ciprofloxacin. Steadily increasing numbers of nalidixic acid, cefotaxime, and ciprofloxacin-resistant isolates, but decreasing numbers of multidrug resistance isolates were detected during the study period. Detection of quinolone genes in 114 nalidixic acid-resistant isolates showed that 58.3% (67/114) harbored plasmid-mediated quinolone resistance (PMQR) genes [aac(6´)-Ib-cr, qnrA, qnrB, oqxAB, qepA, qnrS, and qnrD] and 98.2% (112/114) exhibited mutations in quinolone resistance determining regions [gyrA, parC, and parE]. Furthermore, we detected beta-lactamases genes in the ceftriaxone-resistant isolates. The most common were bla_TEM-1 (93.3%), followed by bla_CTX-M-55 (40%), bla_CMY-2 (33.3%), and bla_OXA-1 (33.3%). Finally, a range of pulsed-field gel electrophoresis patterns were detected among the Salmonella Enteritidis and Salmonella Typhimurium isolates.

Conclusion

High rates of multidrug resistance and steadily increasing cefotaxime and ciprofloxacin-resistant iNTS could pose a significant challenge for the effective treatment of salmonellosis in China.

Acute hepatitis and pancytopenia related to non-typhoidal salmonella infection in a human immunodeficiency virus-infected patient

Non-typhoidal salmonella (NTS) are food-borne pathogens resulting in self-limiting acute gastroenteritis, but also more severe, invasive and sometimes recurrent bacteremia with atypical organ involvement in immunocompromised adults, particularly with human immunodeficiency virus (HIV) infection. Here we present a case of acute hepatitis and pancytopenia related to a non-typhoidal agent, Salmonella enterica subspecies enterica serovar Enteritidis, in an HIV-infected patient, the first case in the literature. As presented in our case, in management of NTS infection in immunocompromised patients, the first target is the control of bacteremia and then administration of antiretroviral therapy to improve patients’ immunity. Therefore, underlying immunosuppression should be excluded in patients presenting with NTS bacteremia, especially in the absence of gastroenteritis. On the other hand, atypical organ involvement and abnormal laboratory findings in HIV infection should prompt investigations for opportunistic pathogens.

Modeling and Cost Benefit Analysis to Guide Deployment of POC Diagnostics for Non-typhoidal Salmonella Infections with Antimicrobial Resistance

Invasive non-typhoidal Salmonella (NTS) is among the leading causes of blood stream infections in sub-Saharan Africa and other developing regions, especially among pediatric populations. Invasive NTS can be difficult to treat and have high case-fatality rates, in part due to emergence of strains resistant to broad-spectrum antibiotics. Furthermore, improper treatment contributes to increased antibiotic resistance and death. Point of care (POC) diagnostic tests that rapidly identify invasive NTS infection, and differentiate between resistant and non-resistant strains, may greatly improve patient outcomes and decrease resistance at the community level. Here we present for the first time a model for NTS dynamics in high risk populations that can analyze the potential advantages and disadvantages of four strategies involving POC diagnostic deployment, and the resulting impact on antimicrobial treatment for patients. Our analysis strongly supports the use of POC diagnostics coupled with targeted antibiotic use for patients upon arrival in the clinic for optimal patient and public health outcomes. We show that even the use of imperfect POC diagnostics can significantly reduce total costs and number of deaths, provided that the diagnostic gives results quickly enough that patients are likely to return or stay to receive targeted treatment.