Typhoidal and non-typhoidal Salmonella infections in Africa

Genomic identification of a pair of multidrug-resistant but non-pathogenic Salmonella enterica serovar Goldcoast isolates in southeast China

Introduction

Salmonella is an important foodborne pathogen that can induce severe diseases such as gastrointestinal disease and typhoid fever. Accumulating evidence revealed that Salmonella's resistance to antibiotics also seriously affects human health. Pathogenic Salmonella enterica serovar Goldcoast (S. Goldcoast) was first detected in 2010 in China and was predicted to have an increasing tendency.

Methods

The MacConkey agar, Salmonella Shigella agar, three-sugar iron agar slant, and Gram-stained microscopic examination were used for strain identification. Gram-negative bacteria identification cards explored more properties of the isolates, while antimicrobial susceptibility testing was used to examine the multidrug resistance. The 2nd and 3rd generation sequencing revealed the genetic information of the isolates.

Results

Two non-pathogenic isolates with multidrug resistance, JS33 and JS34, harbored 42 antibiotic-resistant genes (ARGs) in contig1 and 13 ARGs in contig2, were isolated from a healthy donor living in southeast China and identified as S. Goldcoast (6,8:r:l,w). Interestingly, JS33 and JS34 showed identical responses to more than 20 antimicrobial agents and were resistant to ampicillin, selectrin, chloramphenicol, tetracycline, and streptomycin. However, JS33 differed from JS34 in hydrogen sulfide (H2S) generation. The genomic sequencing identified a deletion in thiosulfate reductase (K08352) in JS34.

Discussion

H2S is an essential physiological regulator linked to inflammation and cancer. Therefore, genomic identification of JS33 and JS34 provided us with a better understanding of drug resistance and could be used as model strains to study the effects of microbial H2S production on the host. Since JS33 and JS34 did not induce gastrointestinal infection or other clinical symptoms as previously reported, the appearance of non-pathogenic S. Goldcoast in southeast China warned us to prepare for the prevalence of antimicrobial-resistant S. Goldcoast in China.

Genetic engineering of Salmonella spp. for novel vaccine strategies and therapeutics

Salmonella enterica is a diverse species that infects both humans and animals. S. enterica subspecies enterica consists of more than 1,500 serovars. Unlike typhoidal Salmonella serovars which are human host-restricted, non-typhoidal Salmonella (NTS) serovars are associated with foodborne illnesses worldwide and are transmitted via the food chain. Additionally, NTS serovars can cause disease in livestock animals causing significant economic losses. Salmonella is a well-studied model organism that is easy to manipulate and evaluate in animal models of infection. Advances in genetic engineering approaches in recent years have led to the development of Salmonella vaccines for both humans and animals. In this review, we focus on current progress of recombinant live-attenuated Salmonella vaccines, their use as a source of antigens for parenteral vaccines, their use as live-vector vaccines to deliver foreign antigens, and their use as therapeutic cancer vaccines in humans. We also describe development of live-attenuated Salmonella vaccines and live-vector vaccines for use in animals.

A c-di-GMP binding effector STM0435 modulates flagellar motility and pathogenicity in Salmonella

Flagella play a crucial role in the invasion process of Salmonella and function as a significant antigen that triggers host pyroptosis. Regulation of flagellar biogenesis is essential for both pathogenicity and immune escape of Salmonella. We identified the conserved and unknown function protein STM0435 as a new flagellar regulator. The ∆stm0435 strain exhibited higher pathogenicity in both cellular and animal infection experiments than the wild-type Salmonella. Proteomic and transcriptomic analyses demonstrated dramatic increases in almost all flagellar genes in the ∆stm0435 strain compared to wild-type Salmonella. In a surface plasmon resonance assay, purified STM0435 protein-bound c-di-GMP had an affinity of ~8.383 µM. The crystal structures of apo-STM0435 and STM0435&c-di-GMP complex were determined. Structural analysis revealed that R33, R137, and D138 of STM0435 were essential for c-di-GMP binding. A Salmonella with STM1987 (GGDEF protein) or STM4264 (EAL protein) overexpression exhibits completely different motility behaviours, indicating that the binding of c-di-GMP to STM0435 promotes its inhibitory effect on Salmonella flagellar biogenesis.

Defense mechanisms of Salmonella against antibiotics: a review

Salmonella is a foodborne pathogenic bacterium that causes salmonellosis worldwide. Also, Salmonella is considered a serious problem for food safety and public health. Several antimicrobial classes including aminoglycosides, tetracyclines, phenols, and β-Lactams are used to treat Salmonella infections. Antibiotics have been prescribed for decades to treat infections caused by bacteria in human and animal healthcare. However, intensive use of antibiotics resulted in antibiotic resistance (AR) among several foodborne bacteria including Salmonella. Furthermore, multi-drug resistance (MDR) of Salmonella has increased dramatically. In addition to MDR Salmonella, extensively drug resistant (XDR) as well as pan drug resistant (PDR) Salmonella were reported globally. Therefore, increasing AR is becoming a serious universal public health crisis. Salmonella developed many mechanisms to ensure its survival against antimicrobials. The most prominent defense mechanisms against these antibiotics include enzymatic inactivation, expelling drugs from the cell through efflux pumps, altering the structure of drugs, and changing or protecting the targets of drugs. Additionally, the formation of biofilms and plasmid-mediated AR by Salmonella, enhancing its resistance to various antibiotics, making it a challenging pathogen in both healthcare and food industry settings. This review focuses exclusively on providing a detailed overview of the mechanisms of AR in Salmonella.

Inter-individual and inter-regional variability of breast milk antibody reactivity to bacterial lipopolysaccharides

Breast milk is a vital source of nutrients, prebiotics, probiotics, and protective factors, including antibodies, immune cells and antimicrobial proteins. Using bacterial lipopolysaccharide arrays, we investigated the reactivity and specificity of breast milk antibodies towards microbial antigens, comparing samples from rural Kenya and urban Switzerland. Results showed considerable variability in antibody reactivity both within and between these locations. Kenyan breast milk demonstrated broad reactivity to bacterial lipopolysaccharides, likely due to increased microbial exposure. Antibodies primarily recognized the O-antigens of lipopolysaccharides and showed strong binding to specific carbohydrate motifs. Notably, antibodies against specific Escherichia coli O-antigens showed cross-reactivity with parasitic pathogens like Leishmania major and Plasmodium falciparum, thus showing that antibodies reacting against lipopolysaccharide O-antigens can recognize a wide range of antigens beyond bacteria. The observed diversity in antigen recognition highlights the significance of breast milk in safeguarding infants from infections, particularly those prevalent in specific geographic regions. The findings also offer insights for potential immunobiotic strategies to augment natural antibody-mediated defense against diverse pathogens.

A Systemic Review on Fitness and Survival of Salmonella in Dynamic Environment and Conceivable Ways of Its Mitigation

Gastroenteritis caused by non-typhoidal Salmonella still prevails resulting in several recent outbreaks affecting many people worldwide. The presence of invasive non-typhoidal Salmonella is exemplified by several characteristic symptoms and their severity relies on prominent risk factors. The persistence of this pathogen can be attributed to its broad host range, complex pathogenicity and virulence and adeptness in survival under challenging conditions inside the host. Moreover, a peculiar aid of the ever-changing climatic conditions grants this organism with remarkable potential to survive within the environment. Abusive use of antibiotics for the treatment of gastroenteritis has led to the emergence of multiple drug resistance, making the infections difficult to treat. This review emphasizes the importance of early detection of Salmonella, along with strategies for accomplishing it, as well as exploring alternative treatment approaches. The exceptional characteristics exhibited by Salmonella, like strategies of infection, persistence, and survival parallelly with multiple drug resistance, make this pathogen a prominent concern to human health.

Genomic characterization, in vitro, and preclinical evaluation of two microencapsulated lytic phages VB_ST_E15 and VB_ST_SPNIS2 against clinical multidrug-resistant Salmonella serovars

BACKGROUND

Salmonella infections continue to be one of the essential public health issues threatening millions of people. With the increasing occurrence of resistance against conventionally used antibiotics, the search for alternatives has become crucial. In this study, we aimed to isolate, characterize, and evaluate two lytic bacteriophages against clinically isolated multidrug-resistant (MDR) Salmonella serovars.

METHODS

Screening for the phage lytic activity was performed using a spot test. Characterization of the isolated phages was done by determining the host range, longevity test, and the effect of temperature, pH, organic solvents, and morphological characterization using a transmission electron microscope. Genomic analysis was performed using Oxford nanopore sequencing. The lytic activities of the free phage lysates and formulated phage as microencapsulated were evaluated both in vitro and in vivo.

RESULTS

Two phages (VB_ST_E15 and VB_ST_SPNIS2) were successfully isolated and showed lytic strong activities against MDR Salmonella (S.) Typhimurium ATCC 14,028, S. Paratyphi A, and S. Typhi. The two phages survived at the tested temperatures, maintained their infectivity for 90 days, and retained their activity until 60 °C with thermal inactivation at 65 °C. They were lytic at a pH range from 3 to 11 but lost their activities at extremely acidic or alkaline pH. The phages could withstand the organic solvents but were completely inactivated by 100% ethanol. Both phages were classified under the order Caudoviricetes, and Genus: Uetakevirus. Their genomic sequences were assembled, annotated, and submitted to the NCBI GenBank database (OR757455 and OR757456). The preclinical evaluation using the murine animal model revealed that the two-phage cocktail managed MDR Salmonella infection as evidenced by the reduction in the bacterial burden, increased animal weight, and histopathological examination.

CONCLUSION

The two encapsulated phage formulas could be considered promising candidates for the management of MDR Salmonella-associated infections and clinical analysis should be undertaken to evaluate their potential use in humans.

Comparative Transcriptomic Analysis of Flagellar-Associated Genes in Salmonella Typhimurium and Its rnc Mutant

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a globally recognized foodborne pathogen that affects both animals and humans. Endoribonucleases mediate RNA processing and degradation in the adaptation of bacteria to environmental changes and have been linked to the pathogenicity of S. Typhimurium. Not much is known about the specific regulatory mechanisms of these enzymes in S. Typhimurium, particularly in the context of environmental adaptation. Thus, this study carried out a comparative transcriptomic analysis of wild-type S. Typhimurium SL1344 and its mutant (∆rnc), which lacks the rnc gene encoding RNase III, thereby elucidating the detailed regulatory characteristics that can be attributed to the rnc gene. Global gene expression analysis revealed that the ∆rnc strain exhibited 410 upregulated and 301 downregulated genes (fold-change > 1.5 and p < 0.05), as compared to the wild-type strain. Subsequent bioinformatics analysis indicated that these differentially expressed genes are involved in various physiological functions, in both the wild-type and ∆rnc strains. This study provides evidence for the critical role of RNase III as a general positive regulator of flagellar-associated genes and its involvement in the pathogenicity of S. Typhimurium.

Deciphering Target Protein Cascade in Salmonella typhi Biofilm using Genomic Data Mining, and Protein-protein Interaction

Background

Salmonella typhi biofilm confers a serious public health issue for lengthy periods and the rise in antibiotic resistance and death rate. Biofilm generation has rendered even the most potent antibiotics ineffective in controlling the illness, and the S. typhi outbreak has turned into a fatal disease typhoid. S. typhi infection has also been connected to other deadly illnesses, such as a gall bladder cancer. The virulence of this disease is due to the interaction of numerous genes and proteins of S. typhi.

Objective

The study aimed to identify a cascade of target proteins in S. typhi biofilm condition with the help of genomic data mining and protein-protein interaction analysis.

Methods

The goal of this study was to notice some important pharmacological targets in S. typhi. using genomic data mining, and protein-protein interaction approaches were used so that new drugs could be developed to combat the disease.

Results

In this study, we identified 15 potential target proteins that are critical for S. typhi biofilm growth and maturation. Three proteins, CsgD, AdrA, and BcsA, were deciphered with their significant role in the synthesis of cellulose, a critical component of biofilm's extracellular matrix. The CsgD protein was also shown to have high interconnectedness and strong interactions with other important target proteins of S. typhi. As a result, it has been concluded that CsgD is involved in a range of activities, including cellulose synthesis, bacterial pathogenicity, quorum sensing, and bacterial virulence.

Conclusion

All identified targets in this study possess hydrophobic properties, and their cellular localization offered proof of a potent therapeutic target. Overall results of this study, drug target shortage in S. typhi is also spotlighted, and we believe that obtained result could be useful for the design and development of some potent anti-salmonella agents for typhoid fever in the future.

Prevention and Control of Human Salmonella enterica Infections: An Implication in Food Safety

Salmonella is a foodborne zoonotic pathogen causing diarrhoeal disease to humans after consuming contaminated water, animal, and plant products. The bacterium is the third leading cause of human death among diarrhoeal diseases worldwide. Therefore, human salmonellosis is of public health concern demanding integrated interventions against the causative agent, Salmonella enterica. The prevention of salmonellosis in humans is intricate due to several factors, including an immune-stable individual infected with S. enterica continuing to shed live bacteria without showing any clinical signs. Similarly, the asymptomatic Salmonella animals are the source of salmonellosis in humans after consuming contaminated food products. Furthermore, the contaminated products of plant and animal origin are a menace in food industries due to Salmonella biofilms, which enhance colonization, persistence, and survival of bacteria on equipment. The contaminated food products resulting from bacteria on equipment offset the economic competition of food industries and partner institutions in international business. The most worldwide prevalent broad-range Salmonella serovars affecting humans are Salmonella Typhimurium and Salmonella Enteritidis, and poultry products, among others, are the primary source of infection. The broader range of Salmonella serovars creates concern over multiple strategies for preventing and controlling Salmonella contamination in foods to enhance food safety for humans. Among the strategies for preventing and controlling Salmonella spread in animal and plant products include biosecurity measures, isolation and quarantine, epidemiological surveillance, farming systems, herbs and spices, and vaccination. Other measures are the application of phages, probiotics, prebiotics, and nanoparticles reduced and capped with antimicrobial agents. Therefore, Salmonella-free products, such as beef, pork, poultry meat, eggs, milk, and plant foods, such as vegetables and fruits, will prevent humans from Salmonella infection. This review explains Salmonella infection in humans caused by consuming contaminated foods and the interventions against Salmonella contamination in foods to enhance food safety and quality for humans.

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.

Impact of childhood malnutrition and intestinal microbiota on MDR infections

The global burden of infection from MDR organisms (MDROs) disproportionately affects children residing in low- and middle-income countries and those with increased healthcare exposure. These populations have high rates of malnutrition making them increasingly vulnerable to infection with intestinal-derived pathogens. Malnourished children experience increased incidence of intestinal carriage and invasive infection with intestinal-derived MDROs including ESBL- and carbapenemase-producing Enterobacterales. However, the relationship between malnutrition and MDRO infection remains to be clearly defined. Impairment in intestinal barrier function and innate and adaptive immunity in malnutrition increases the risk for infection with intestinal-derived pathogens, and there is an increasing appreciation of the role of the intestinal microbiota in this process. Current evidence from human studies and animal models suggests that diet and the intestinal microbiota influence each other to determine nutritional status, with important implications for infectious outcomes. These insights are crucial to developing microbiota-targeted strategies aimed at reversing the growing burden of MDRO infections in malnourished populations worldwide.

Effects of Lactobacillus fermentum Administration on Intestinal Morphometry and Antibody Serum Levels in Salmonella-Infantis-Challenged Chickens

There are no studies reporting the effects of Salmonella enterica subsp. enterica serovar Infantis (S. Infantis) on intestinal architecture and immunoglobulin serum levels in chickens. Here, we measured these parameters and hypothesized whether probiotic administration could modulate the observed outcomes. Two-hundred 1-day-old COBB 500 male chicks were allocated into four groups: (I) the control, (II) the group treated with L. fermentum, (III) the group exposed to S. Infantis, and (IV) the group inoculated with both bacteria. At 11 days post infection, blood was gathered from animals which were then euthanized, and samples from the small intestine were collected. Intestinal conditions, as well as IgA and IgM serum levels, were assessed. S. Infantis reduced villus-height-to-crypt-depth (VH:CD) ratios in duodenal, jejunal, and ileal sections compared to control conditions, although no differences were found regarding the number of goblet cells, muc-2 expression, and immunoglobulin concentration. L. fermentum improved intestinal measurements compared to the control; this effect was also evidenced in birds infected with S. Infantis. IgM serum levels augmented in response to the probiotic in infected animals. Certainly, the application of L. fermentum elicited positive outcomes in S. Infantis-challenged chickens and thus must be considered for developing novel treatments designed to reduce unwanted infections.

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.

Host acid signal controls Salmonella flagella biogenesis through CadC-YdiV axis

Upon entering host cells, Salmonella quickly turns off flagella biogenesis to avoid recognition by the host immune system. However, it is not clear which host signal(s) Salmonella senses to initiate flagellum control. Here, we demonstrate that the acid signal can suppress flagella synthesis and motility of Salmonella, and this occurs after the transcription of master flagellar gene flhDC and depends on the anti-FlhDC factor YdiV. YdiV expression is activated after acid treatment. A global screen with ydiV promoter DNA and total protein from acid-treated Salmonella revealed a novel regulator of YdiV, the acid-related transcription factor CadC. Further studies showed that CadC_C, the DNA binding domain of CadC, directly binds to a 33 nt region of the ydiV promoter with a 0.2 μM K_D affinity. Furthermore, CadC could separate H-NS-ydiV promoter DNA complex to form CadC-DNA complex at a low concentration. Structural simulation and mutagenesis assays revealed that H43 and W106 of CadC are essential for ydiV promoter binding. No acid-induced flagellum control phenotype was observed in cadC mutant or ydiV mutant strains, suggesting that flagellum control during acid adaption is dependent on CadC and YdiV. The intracellular survival ability of cadC mutant strain decreased significantly compared with WT strain while the flagellin expression could not be effectively controlled in the cadC mutant strain when surviving within host cells. Together, our results demonstrated that acid stress acts as an important host signal to trigger Salmonella flagellum control through the CadC-YdiV-FlhDC axis, allowing Salmonella to sense a hostile environment and regulate flagellar synthesis during infection.

A PMAxxTM qPCR Assay Reveals That Dietary Administration of the Microalgae Tetraselmis chuii Does Not Affect Salmonella Infantis Caecal Content in Early-Treated Broiler Chickens

Salmonella enterica serovars cause infections in humans. S. enterica subsp. enterica serovar Infantis is considered relevant and is commonly reported in poultry products. Evaluating innovative approaches for resisting colonization in animals could contribute to the goal of reducing potential human infections. Microalgae represent a source of molecules associated with performance and health improvement in chickens. Tetraselmis chuii synthesizes fermentable polysaccharides as part of their cell wall content; these sugars are known for influencing caecal bacterial diversity. We hypothesized if its dietary administration could exert a positive effect on caecal microbiota in favor of a reduced S. Infantis load. A total of 72 one-day-old broiler chickens (COBB 500) were randomly allocated into three groups: a control, a group infected with bacteria (day 4), and a group challenged with S. Infantis but fed a microalgae-based diet. Caecal samples (n = 8) were collected two days post-infection. A PMAxxTM-based qPCR approach was developed to assess differences regarding bacterial viable load between groups. The inclusion of the microalga did not modify S. Infantis content, although the assay proved to be efficient, sensitive, and repeatable. The utilized scheme could serve as a foundation for developing novel PCR-based methodologies for estimating Salmonella colonization.

Genomic characterization of invasive typhoidal and non-typhoidal Salmonella in southwestern Nigeria

BACKGROUND

Salmonellosis causes significant morbidity and mortality in Africa. Information on lineages of invasive Salmonella circulating in Nigeria is sparse.

METHODS

Salmonella enterica isolated from blood (n = 60) and cerebrospinal fluid (CSF, n = 3) between 2016 and 2020 from five tertiary hospitals in southwest Nigeria were antimicrobial susceptibility-tested and Illumina-sequenced. Genomes were analysed using publicly-available bioinformatic tools.

RESULTS

Isolates and sequence types (STs) from blood were S. Typhi [ST1, n = 1 and ST2, n = 43] and invasive non-typhoidal Salmonella (iNTS) (S. Enteritidis [ST11, n = 7], S. Durham [ST10, n = 2], S. Rissen [ST8756, n = 2], S. Chester [ST2063, n = 1], S. Dublin [ST10, n = 1], S. Infantis [ST603, n = 1], S. Telelkebir [ST8757, n = 1] and S. Typhimurium [ST313, n = 1]). S. Typhi ST2 (n = 2) and S. Adabraka ST8757 (n = 1) were recovered from CSF. Most S. Typhi belonged to genotype 3.1.1 (n = 44), carried an IncY plasmid, had several antibiotic resistance genes (ARGs) including blaTEM-1 (n = 38), aph(6)-Id (n = 32), tet(A) (n = 33), sul2 (n = 32), dfrA14 (n = 30) as well as quinolone resistance-conferring gyrA_S83Y single-nucleotide polymorphisms (n = 37). All S. Enteritidis harboured aph(3")-Ib, blaTEM-1, catA1, dfrA7, sul1, sul2, tet(B) genes, and a single ARG, qnrB19, was detected in S. Telelkebir. Typhoidal toxins cdtB, pltA and pltB were detected in S. Typhi, Rissen, Chester, and Telelkebir.

CONCLUSION

Most invasive salmonelloses in southwest Nigeria are vaccine-preventable infections due to multidrug-resistant, West African dominant S. Typhi lineage 3.1.1. Invasive NTS serovars, including some harbouring typhoidal toxin or resistance genes, represented a third of the isolates emphasizing the need for better diagnosis and surveillance.

Occurrence and antimicrobial susceptibility patterns of Salmonella species from poultry farms in Ibadan, Nigeria

Background: Salmonella species are among the major foodborne pathogens causing diseases of economic and public health implications in poultry and humans globally.Objective: This study aimed to determine the occurrence and antimicrobial susceptibility patterns of Salmonella isolates from chickens in poultry farms in Ibadan, Southwest Nigeria.Methods: Cloacal swab samples (n = 360) were obtained from chickens randomly selected from 10 poultry farms in five local government areas of Ibadan, Oyo State, from 04 April 2018 to 20 November 2018. Bacterial identification and antimicrobial susceptibility testing were performed using established protocols. Data were analysed using descriptive statistics and Pearson’s chi-squared test at P ≤ 0.05 significance level.Results: The overall prevalence of Salmonella was 21.4%. There were statistically significant associations between Salmonella prevalence and the farm location (p = 0.003), age of chickens (p  0.001), and health status of chickens (p  0.001). All Salmonella isolates (n = 77; 100.0%) were resistant to cefuroxime. The isolates were also highly resistant to cotrimoxazole (n = 74; 96.1%), chloramphenicol (n = 73; 94.8%), meropenem (n = 72; 93.5%), gentamicin (n = 69; 89.6%), and tetracycline (n = 64; 83.1%).Conclusion: The presence of drug-resistant Salmonella in commercial layer chickens in Ibadan is a potential threat to consumer health as it increases the risk of carcass contamination and pathogen propagation, and limits the options to control and treat infections in humans and animals. Well-integrated national surveillance systems for monitoring Salmonella and antimicrobial resistance in poultry are critical. 

Practicalities of implementing burden of disease research in Africa: lessons from a population survey component of our multi-partner FOCAL research project

Background

Collaborative research is being increasingly implemented in Africa to study health-related issues, for example, the lack of evidence on disease burden, in particular for the presumptive high load of foodborne diseases. The FOCAL (Foodborne disease epidemiology, surveillance, and control in African LMIC) Project is a multi-partner study that includes a population survey to estimate the foodborne disease burden in four African low- and middle-income countries (LMICs). Our multi-partner study team had members from seven countries, all of whom contributed to the project from the grant application stage, and who play(ed) specific roles in designing and implementing the population survey.

Main text

In this paper, we applied Larkan et al.’s framework for successful research partnerships in global health to self-evaluate our project’s collaboration, management, and implementation process. Our partnership formation considered the interplay and balance between operations and relations. Using Larkan et al.’s seven core concepts (i.e., focus, values, equity, benefit, communication, leadership, and resolution), we reviewed the process stated above in an African context.

Conclusion

Through our current partnership and research implementing a population survey to study disease burden in four African LMICs, we observed that successful partnerships need to consider these core concepts explicitly, apply the essential leadership attributes, perform assessment of external contexts before designing the research, and expect differences in work culture. While some of these experiences are common to research projects in general, the other best practices and challenges we discussed can help inform future foodborne disease burden work in Africa.

A review of Leaves and Seeds Moringa oleifera Extract: The potential Moringa oleifera as Antibacterial, Anti-Inflammatory, Antidiarrhoeal, And Antiulcer Approaches To Bacterial Gastroenteritis

BACKGROUND: Bacterial gastroenteritis is a disease in the tropics in the form of inflammation of the stomach and intestines due to several bacteria, such as Salmonella, Campylobacter, Shigella, Escherichia coli, Vibrio, Yersinia, and Listeria with symptoms of diarrhea without or with vomiting and frequent fever. Gastroenteritis is a global disease with the highest prevalence in the agricultural community, especially farmers and fishermen. AIM: This research is to determine the potential of leaf and seed extract Moringa oleifera as an alternative therapy for bacterial gastroenteritis. METHODS: A literature review approach derived from the analysis and synthesis of various related references is used. The author selects journals full text and books published in the last ten years maximum through several databases, namely PubMed, Google Scholar, ScienceDirect, and Cochrane with the keywords: diarrhea, gastroenteritis, antibacterial, antiulcer, anti-inflammation, and M. oleifera. RESULTS: Seed and leaf extract M. oleifera played a role in preventing some of the effects of the pathogenesis of diarrhea due to bacterial infection. Methanol, N-hexane, ethyl acetate, flavonoids, phenols, saponins, alkaloids, tannins, and steroids from seed and leaf extract M. oleifera have antibacterial effects. The content of quercetin has an anti-inflammatory effect. The content of tannins, flavonoids, and alkaloids has antidiarrheal activity. The content of ethanol and tannins has an antiulcer effect. This potential can help cure patients with bacterial gastroenteritis. CONCLUSION: Leaf and seed extract of M. oleifera has good antibacterial, anti-inflammatory, antiulcer, and antidiarrheal potential for the treatment of bacterial gastroenteritis.

Antimicrobial resistance and virulence genes in Salmonella enterica serovars isolated from droppings of layer chicken in two farms in Nigeria

AIM

This study aimed to investigate the isolation rate, antibiotic resistance, and virulence genes of Salmonella enterica serovar from two commercial farms in Nigeria.

METHODS AND RESULTS

Salmonella isolation was performed according to the United States Food and Drug Agency (USFDA) method. Serotyping, antimicrobial susceptibility testing, detection of resistance and virulence genes were done using the Kauffman-White Scheme, disc diffusion, minimum inhibitory concentration, and real-time polymerase chain reaction techniques. Salmonella serovars were isolated from only farm A at 22/50 (44.0%) while none were isolated from farm B. Salmonella Typhi, 9 (40.9%); Salmonella Typhimurium, 2 (9.1%), Salmonella Enteritidis, 2 (9.1%), Salmonella Pullorum, 1 (4.5%), Salmonella Kentucky, 4 (18.2%) were identified while 4 (18.2%) were untypable. Sixteen isolates (72.7%) showed multiple drug resistance and 17 different resistance profile types with AMP-CHL-TRM-SXT as the most prevalent pattern. Resistance genes (blaTEM, 12/22 (54.5%) and virulence genes (InvA, sopB, mgtC, and spi4D, 22/22 (100.0%), ssaQ, 16/22 (72.7%), and spvC, 13/22 (59.1%) were found, while blaSHV, blaCTX-M, floR, tetA, tetB, tetG, and LJSGI-1 genes were absent.

CONCLUSION

Pathogenic Salmonella were isolated from the chicken droppings in this study. Most of these strains were resistant to antibiotics and possessed characteristics of virulence.

SIGNIFICANCE AND IMPACT OF THE STUDY

Chicken droppings from this study area contained pathogenic strains of Salmonella and a rare occurrence of Salmonella Typhi. The study revealed that the environment and the food chain could be at risk of contamination of highly virulent and antimicrobial-resistant strains of Salmonella. These could affect the profitability of the poultry industry and food consumption. There is a need for caution in indiscriminate disposal of poultry waste and the use of uncomposted chicken droppings in soil amendment.

Role of medicinal plants from North Western Himalayas as an efflux pump inhibitor against MDR AcrAB-TolC Salmonella enterica serovar typhimurium: In vitro and In silico studies

ETHNOPHARMACOLOGICAL RELEVANCE

Zingiber officinale Roscoe has been utilized traditionally to cure various diseases like cold, cough, diarrhoea, nausea, asthma, vomiting, toothache, stomach upset, respiratory disorders, joint pain, and throat infection. It is also consumed as spices and ginger tea.

AIM OF THE STUDY

The current study was aimed to identify the phytocompounds of traditional medicinal plants of North-Western Himalaya that could inhibit the AcrAB-TolC efflux pump activity of Salmonella typhimurium and become sensitive to antibiotic killing at reduced dosage.

MATERIAL AND METHODS

Medicinal plant extracts were prepared using methanol, aqueous, and ethyl acetate and tested for efflux pump inhibitory activity of Salmonella typhimurium NKS70, NKS174, and NKS773 strains using Ethidium Bromide (EtBr)-agar cartwheel assay. Synergism was assessed by the agar well diffusion method and EPI activity by berberine uptake and EtBr efflux inhibition assays. Microdilution method and checkerboard assays were done to determine the minimum inhibitory concentration (MIC) and fractional inhibitory concentration index (FICI) respectively for a bioactive compound. To validate the phytocompound and efflux pump interaction, molecular docking with 6IE8 (RamA) and 6IE9 (RamR) targets was done using autoDock vina software. Toxicity prediction and drug-likeness were predicted by using ProTox-II and Molinspiration respectively.

RESULTS

Methanolic and ethyl acetate extracts of P. integerrima, O. sanctum, C. asiatica, M. charantia, Z. officinale, and W. somnifera in combination with ciprofloxacin and tetracycline showed synergistic antimicrobial activity with GIIs of 0.61-1.32 and GIIs 0.56-1.35 respectively. Methanolic extract of Z. officinal enhanced the antimicrobial potency of berberine (2 to 4-folds) and increased the EtBr accumulation. Furthermore, bioassay-guided fractionation leads to the identification of lariciresinol in ethyl acetate fraction, which decreased the MIC by 2-to 4-folds. The ΣFIC values varied from 0.30 to 0.55 with tetracycline, that indicated synergistic/additive effects. Lariciresinol also showed a good binding affinity with 6IE8 (-7.4 kcal mol-1) and 6IE9 (-8.2 kcal mol-1), which is comparable to tetracycline and chenodeoxycholic acid. Lariciresinol followed Lipinski's rule of five.

CONCLUSION

The data suggest that lariciresinol from Z. officinale could be a potential efflux pump inhibitor that could lead to effective killing of drug resistant Salmonella typhimurium at lower MIC. Molecular docking confirmed the antibacterial EPI mechanism of lariciresinol in Salmonella typhimurium and confirmed to be safe for future use.

Host acid signal controls Salmonella flagella biogenesis through CadC-YdiV axis

Upon entering host cells, Salmonella quickly turns off flagella biogenesis to avoid recognition by the host immune system. However, it is not clear which host signal(s) Salmonella senses to initiate flagellum control. Here, we demonstrate that the acid signal can suppress flagella synthesis and motility of Salmonella, and this occurs after the transcription of master flagellar gene flhDC and depends on the anti-FlhDC factor YdiV. YdiV expression is activated after acid treatment. A global screen with ydiV promoter DNA and total protein from acid-treated Salmonella revealed a novel regulator of YdiV, the acid-related transcription factor CadC. Further studies showed that CadC_C, the DNA binding domain of CadC, directly binds to a 33 nt region of the ydiV promoter with a 0.2 μM K_D affinity. Furthermore, CadC could separate H-NS-ydiV promoter DNA complex to form CadC-DNA complex at a low concentration. Structural simulation and mutagenesis assays revealed that H43 and W106 of CadC are essential for ydiV promoter binding. No acid-induced flagellum control phenotype was observed in cadC mutant or ydiV mutant strains, suggesting that flagellum control during acid adaption is dependent on CadC and YdiV. The intracellular survival ability of cadC mutant strain decreased significantly compared with WT strain while the flagellin expression could not be effectively controlled in the cadC mutant strain when surviving within host cells. Together, our results demonstrated that acid stress acts as an important host signal to trigger Salmonella flagellum control through the CadC-YdiV-FlhDC axis, allowing Salmonella to sense a hostile environment and regulate flagellar synthesis during infection.

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

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

Prevalence and Characteristics of Ceftriaxone-Resistant Salmonella in Children's Hospital in Hangzhou, China

The non-Typhi Salmonella (NTS) infection is critical to children's health, and the ceftriaxone is the important empirical treatment choice. With the increase resistance rate of ceftriaxone in Salmonella, the molecular epidemiology and resistance mechanism of ceftriaxone-resistant Salmonella needs to be studied. From July 2019 to July 2020, a total of 205 NTS isolates were collected, 195 of which (95.1%) were cultured from stool, but 10 isolates were isolated from an extraintestinal site. Serogroup B accounted for the vast majority (137/205) among the isolates. Fifty-three isolates were resistant to ceftriaxone, and 50 were isolated from children younger than 4years of age. The resistance rates for ceftriaxone, ciprofloxacin, and levofloxacin were significantly higher in younger children than the older children. The resistance genes in the ceftriaxone-susceptible isolates were detected by PCR, and ceftriaxone-resistant Salmonella were selected for further whole-genome sequencing. Whole-genome analysis showed that serotype Typhimurium and its monophasic variant was the most prevalent in ceftriaxone-resistant isolates (37/53), which comprised ST34 (33/53), ST19 (2/53), and ST99 (2/53), and they were close related in the phylogenetic tree. However, the other isolates were diverse, which included one Enteritidis (ST11), one Indiana (ST17), one Derby (ST40), four Kentucky (ST198), two Goldcoast (ST2529, ST358), one Muenster (ST321), one Virchow (ST359), one Rissen (ST469), one Kedougou (ST1543), two Uganda (ST684), and one Kottbus (ST8839). Moreover, CTX-M-55 ESBLs production (33/53) was found to be mainly responsible for ceftriaxone resistance, followed by bla _CTX-M-65 (12/53), bla _CTX-M-14 (4/53), bla _CTX-M-9 (2/53), bla _CTX-M-64 (1/53), bla _CTX-M-130 (1/53), and bla _CMY-2 (1/53). ISEcp1, IS903B, IS Kpn26, IS1F, and IS26 were connected to antimicrobial resistance genes transfer. In conclusion, the dissemination of ESBL-producing Salmonella isolates resulted in an increased prevalence of ceftriaxone resistance in young children. The high rate of multidrug resistance should be given additional attention.

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.

Epidemiological Investigation of Salmonella enterica Isolates in Children with Diarrhea in Chengdu, China

Background: Children with the immature intestinal immune system are prone to Salmonella infection through the fecal-oral route causing diarrhea. Non-typhoid Salmonella (NTS) is difficult to treat and eliminate due to its zoonosis. Salmonella typhi, including typhoid and paratyphoid A, B, and C, only infect humans and cause invasive infectious diseases. Salmonella typhi infection is serious and requires antibiotic treatment. The bacterial resistance caused by conventional antibacterial drugs brings great difficulties to treatment. Objectives: This study aimed to investigate the epidemiology of S. enterica in children with diarrhea in Chengdu, China. Methods: Fresh stool specimens or rectal swabs from 6656 children aged 1 day to 13 years with diarrhea were collected, cultured, identified, and tested for antimicrobial susceptibility. Analytical Profile index 20E was used for biochemical identification, and the Kirby-Bauer method was used for the bacterial sensitivity test. The whole process was conducted in accordance with the fourth edition of the National Clinical Examination procedures, and the drug sensitivity test was conducted in accordance with the Clinical and Laboratory Standards Institute 2020 guidelines. Results: A total of 649 Salmonella strains were isolated from 6656 children with suspected Salmonella infection, among which the isolation rates of NTS and S. typhi were 8.92% and 0.83%, respectively. The infection rate of S. typhimurium was the highest every year (74.88%). Salmonella infections are on the rise, especially typhimurium, Dublin, Typhi, and London. Paratyphi is unstable, presenting a phenomenon of transition and replacement (the male to female ratio:1.12:1). The infection rate was the lowest within 1 day and 6 months (P < 0.05). Salmonella mainly infected children under 3 years of age, and the positive rate was reported as 88.29%. Within June-September, the infection rate of Salmonella was the highest, with a positive rate of 72.73%. The isolated 649 Salmonella strains had good susceptibility to cefotaxime and ciprofloxacin (87.67% and 79.20%, respectively), almost no susceptibility to ampicillin, and a drug resistance rate of 92.91%. Conclusions: The typhoid and paratyphoid vaccines should be considered together, and vaccines should focus on children under 3 years of age. Antibiotics should be rationally selected according to the drug sensitivity test and disease condition.

Whole Genome Sequencing Analysis of Salmonella enterica Serovar Typhi: History and Current Approaches

In recent years, the advance in whole-genome sequencing technology has changed the study of infectious diseases. The emergence of genome sequencing has improved the understanding of infectious diseases, which has revamped many fields, such as molecular microbiology, epidemiology, infection control, and vaccine production. In this review we discuss the findings of Salmonella enterica serovar Typhi genomes, publicly accessible from the initial complete genome to the recent update of Salmonella enterica serovar Typhi genomes, which has greatly improved Salmonella enterica serovar Typhi and other pathogen genomic research. Significant information on genetic changes, evolution, antimicrobial resistance, virulence, pathogenesis, and investigation from the genome sequencing of S. Typhi is also addressed. This review will gather information on the variation of the Salmonella enterica serovar Typhi genomes and hopefully facilitate our understanding of their genome evolution, dynamics of adaptation, and pathogenesis for the development of the typhoid point-of-care diagnostics, medications, and vaccines.

Evidence and speculation: the response of Salmonella confronted by autophagy in macrophages

Bacteria of the Salmonella genus cause diseases ranging from self-limited gastroenteritis to typhoid fever. Macrophages are immune cells that engulf and restrict Salmonella. These cells will carry Salmonella into the circulatory system and provoke a systemic infection. Therefore, the interaction between macrophages and intracellular Salmonella is vital for its pathogenicity. As one of the immune responses of macrophages, autophagy, along with the fusion of autophagosomes with lysosomes, occupies an important position in eliminating Salmonella. However, Salmonella that can overcome cellular defensive responses and infect neighboring cells must derive strategies to escape autophagy. This review introduces novel findings on Salmonella and macrophage autophagy as a mechanism against infection and explores the strategies used by Salmonella to escape autophagy.

Molecular Detection of Multidrug Resistant Salmonella Species Isolated from Broiler Farm in Bangladesh

Multidrug resistant (MDR) Salmonella are a leading cause of foodborne diseases and serious human health concerns worldwide. In this study we detected MDR Salmonella in broiler chicken along with the resistance genes and class 1 integron gene intl1. A total of 100 samples were collected from broiler farms comprising 50 cloacal swabs, 35 litter and 15 feed samples. Overall prevalence of Salmonella was 35% with the highest detected in cloacal swabs. Among the Salmonella, 30 isolates were confirmed as S. enterica serovar Typhimurium using molecular methods of PCR. Disk diffusion susceptibility test revealed that all the Salmonella were classified as MDR with the highest resistance to tetracycline (97.14%), chloramphenicol (94.28%), ampicillin (82.85%) and streptomycin (77.14%). The most prevalent resistance genotypes were tetA (97.14%), floR (94.28%), bla_TEM-1 (82.85%) and aadA1 (77.14%). In addition, among the MDR Salmonella, 20% were positive for class 1 integron gene (intl1). As far as we know, this is the first study describing the molecular basis of antibiotic resistance in MDR Salmonella from broiler farms in Bangladesh. In addition to tetA, floR, bla_TEM-1, aadA1 and intl1 were also detected in the isolated MDR Salmonella. The detection of MDR Salmonella in broiler chicken carrying intl1 is of serious public health concern because of their zoonotic nature and possibilities to enter into the food chain.

Pattern of increased antimicrobial resistance of Salmonella isolates in the Eastern Province of KSA

OBJECTIVES

The antimicrobial resistance of Salmonella species is increasing worldwide. This study was conducted to determine the pattern of antimicrobial susceptibility of Salmonella species in a tertiary hospital from 2011 to 2018.

METHODS

In this retrospective study, the medical records of all patients with Salmonella infections were reviewed. The clinical, demographic, and microbiological data of the selected patients were analysed.

RESULTS

A total of 752 patients were included. The resistance of Salmonella species to antimicrobial drugs increased from 24.6% in 2011 to 37.8% in 2018 (p = 0.002). By 2018 all Salmonella isolates were completely resistant to cefalotin, cefuroxime, and cefoxitin, while we found some susceptibility to other cephalosporins and ciprofloxacin. The most commonly isolated Salmonella serogroups were groups D (36.5%), C (23.5%), and B (11.7%).

CONCLUSIONS

The incidence of resistance of Salmonella to antibiotics is on the rise. The results of this study highlight the need for an active monitoring system of antibiotic usage in humans and domestic animals.

Identification of Salmonella Bredeney Resistant to Third-Generation Cephalosporins in Saudi Arabia

The rapidly increasing prevalence and spread of antibiotic-resistant Salmonella worldwide have become a thorny problem that poses a serious threat to human health. It is speculated that antibiotic abuse, frequent traveling, and mass gatherings accelerate this threat. To explore this hypothesis, we investigated 13 Salmonella isolates from Medina, Saudi Arabia and 15 from China as the control group using typical methods of serotype identification, antibiotic resistance tests, pulsed-field gel electrophoresis (PFGE), and multi-locus sequence typing (MLST). Our results indicated that the isolates from China showed greater serotype diversity and a higher antimicrobial resistance rate, which was consistent with results from other studies in China. In contrast, the Saudi Arabian isolates were mainly identified as Serovar Bredeney and were resistant to a limited number of antibiotics. Interestingly, two of the Bredeney isolates was resistant to third-generation cephalosporins but sensitive to all other tested antibiotics. To confirm the results and understand the underlying molecular mechanisms of these isolates, whole-genome sequencing (WGS) was performed. We discovered that several cephalosporin resistance-associated genes were shared with other strains, but one gene (LEN-23) was unique. Therefore, to the best of our knowledge, we concluded that this study is the first to report the emergence of Salmonella Bredeney resistant to third-generation cephalosporins in Saudi Arabia.

A review of Salmonella enterica with particular focus on the pathogenicity and virulence factors, host specificity and antimicrobial resistance including multidrug resistance

Salmonella genus represents the most common foodborne pathogens frequently isolated from food-producing animals that is responsible for zoonotic infections in humans and animal species including birds. Thus, Salmonella infections represent a major concern to public health, animals, and food industry worldwide. Salmonella enterica represents the most pathogenic specie and includes > 2600 serovars characterized thus far. Salmonella can be transmitted to humans along the farm-to-fork continuum, commonly through contaminated foods of animal origin, namely poultry and poultry-related products (eggs), pork, fish etc. Some Salmonella serovars are restricted to one specific host commonly referred to as "host-restricted" whereas others have broad host spectrum known as "host-adapted" serovars. For Salmonella to colonize its hosts through invading, attaching, and bypassing the host's intestinal defense mechanisms such as the gastric acid, many virulence markers and determinants have been demonstrated to play crucial role in its pathogenesis; and these factors included flagella, capsule, plasmids, adhesion systems, and type 3 secretion systems encoded on the Salmonella pathogenicity island (SPI)-1 and SPI-2, and other SPIs. The epidemiologically important non-typhoidal Salmonella (NTS) serovars linked with a high burden of foodborne Salmonella outbreaks in humans worldwide included Typhimurium, Enteritidis, Heidelberg, and Newport. The increased number of NTS cases reported through surveillance in recent years from the United States, Europe and low- and middle-income countries of the world suggested that the control programs targeted at reducing the contamination of food animals along the food chain have largely not been successful. Furthermore, the emergence of several clones of Salmonella resistant to multiple antimicrobials worldwide underscores a significant food safety hazard. In this review, we discussed on the historical background, nomenclature and taxonomy, morphological features, physical and biochemical characteristics of NTS with a particular focus on the pathogenicity and virulence factors, host specificity, transmission, and antimicrobial resistance including multidrug resistance and its surveillance.

Expression kinetics of natural resistance associated macrophage protein (NRAMP) genes in Salmonella Typhimurium-infected chicken

Background

Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) is a zoonotic pathogen responsible for severe intestinal pathology in young chickens. Natural resistance-associated macrophage protein (NRAMP) family has been shown to be associated with resistance to intracellular pathogens, including Salmonella Typhimurium. The role of NRAMP proteins in macrophage defence against microbial infection has been ascribed to changes in the metal-ion concentrations inside the bacteria-containing phagosomes. The present study was conducted to investigate tissue-specific (liver, spleen and caecum) expression kinetics of NRAMP gene family (NRAMP1 and NRAMP2) in broilers from day 0 to day 15 after Salmonella Typhimurium challenge concomitant to clinical, blood biochemical and immunological parameters survey.

Results

Clinical symptoms appeared 4 days post-infection (dpi) in infected birds. Symptoms like progressive weakness, anorexia, diarrhoea and lowering of the head were seen in infected birds one-week post-infection. On postmortem examination, liver showed congestion, haemorrhage and necrotic foci on the surface, while as the spleen, lungs and intestines revealed congestion and haemorrhages. Histopathological alterations were principally found in liver comprising of necrosis, reticular endothelial hyperplasia along with mononuclear cell and heterophilic infiltration. Red Blood Cell (RBC) count, Haemoglobin (Hb) and Packed Cell Volume (PCV) decreased significantly (P < 0.05) in blood while heterophil counts increased up to 7 days post-infection. Serum glucose, aspartate transaminase (AST) and alanine transaminase (ALT) enzymes concentrations increased significantly throughout the study. A gradual increase of specific humoral IgG response confirmed Salmonella infection. Meanwhile, expression of NRAMP1 and NRAMP2 genes was differentially regulated after infection in tissues such as liver, spleen and caecum known to be the target of Salmonella Typhimurium replication in the chicken.

Conclusion

Thus the specific roles of NRAMP1 and NRAMP2 genes in Salmonella Typhimurium induced disease may be supposed from their differential expression according to tissues and timing after per os infection. However, these roles remain to be analyzed related to the severity of the disease which can be estimated by blood biochemistry and immunological parameters.

Salmonella serovars and their distribution in Nigerian commercial chicken layer farms

Commercial poultry farms (n° 523), located in all the six regions of Nigeria were sampled with a view to generate baseline information about the distribution of Salmonella serovars in this country. Five different matrices (litter, dust, faeces, feed and water) were collected from each visited farm. Salmonella was isolated from at least one of the five matrices in 228 farms, with a farm prevalence of 43.6% (CI95[39.7-48.3%]). Altogether, 370 of 2615 samples collected (14.1%, CI95[12.8; 15.5%]) contained Salmonella. Considering the number of positive farms and the number of positive samples, it was evident that for the majority of the sampled farms, few samples were positive for Salmonella. With regard to the matrices, there was no difference in Salmonella prevalence among the five matrices considered. Of the 370 isolates serotyped, eighty-two different serotypes were identified and Salmonella Kentucky was identified as having the highest isolation rate in all the matrices sampled (16.2%), followed by S. Poona and S. Elisabethville. S. Kentucky was distributed across the country, whereas the other less frequent serovars had a more circumscribed diffusion. This is one of few comprehensive studies on the occurrence and distribution of Salmonella in commercial chicken layer farms from all the six regions of Nigeria. The relatively high prevalence rate documented in this study may be attributed to the generally poor infrastructure and low biosecurity measures in controlling stray animals, rodents and humans. Data collected could be valuable for instituting effective intervention strategies for Salmonella control in Nigeria and also in other developing countries with a similar poultry industry structure, with the final aim of reducing Salmonella spread in animals and ultimately in humans.

Efflux Pump Overexpression Contributes to Tigecycline Heteroresistance in Salmonella enterica serovar Typhimurium

Bacterial heteroresistance has been identified in several combinations of bacteria and antibiotics, and it complicated the therapeutic strategies. Tigecycline is being used as one of the optimal options for the treatment of infections caused by multidrug-resistant Salmonella. This study investigated whether heterorresistance to tigecycline exists in a Salmonella enterica serovar Typhimurium strain harboring the oqxAB-bearing IncHI2 plasmid pHXY0908. MIC and population analyses were performed to evaluate population-wide susceptibility to tigecycline. The effects of efflux pumps on MIC levels were assessed using the efflux pump inhibitor Phe-Arg-β-naphthylamide, measuring intracellular tigecycline accumulation as well as mRNA levels of regulatory and efflux pump genes. DNA sequencing of regulatory regions were performed and plasmid curing from a resistant strain provided an appropriate control. Results showed that MICs of a parental strain with and without pHXY0908 as well as a plasmid-cured strain 14028/Δp52 were 0.5, 1, and 1 μg/mL, respectively. Population analysis profiling (PAP) illustrated that only the pHXY0908-containg strain was heteroresistant to tigecycline. A fraction of colonies exhibited stable profiles with 4- to 8-fold increases in MIC. The frequencies of emergence of these isolates were higher in the plasmid-containing strain pHXY0908 than either the parental or the 14028/Δp52 strain. Phe-Arg-β-naphthylamide addition restored tigecycline susceptibility of these isolates and intracellular tigecycline accumulation was reduced. Heteroresistant isolates of the strain containing pHXY0908 also had elevated expression of acrB, ramA, and oqxB. DNA sequencing identified numerous mutations in RamR that have been shown to lead to ramA overexpression. In conclusions, heteroresistance to tigecycline in Salmonella enterica serovar Typhimurium was manifested in a plasmid-bearing strain. Our results suggest that this phenotype was associated with overexpression of the AcrAB-TolC and OqxAB efflux pumps.