Epidemiology, Pathogenesis, Genoserotyping, Antimicrobial Resistance, and Prevention and Control of Non-Typhoidal Salmonella Serovars

Non-typhoidal Salmonella contamination of food sources from animal origin in Israel between 2007 and 2021

Non-typhoidal Salmonella (NTS) are one of the main causes of food poisoning, a major global threat for human health. Consumption of contaminated food products of animal origin contributes to majority of the NTS illness outbreaks. Poultry, an important protein source, is considered the main animal source for NTS. However, contamination with different serotypes of NTS may be attributed to various animal hosts. We aimed to determine the prevalence, trends, and potential risk factors for NTS contamination of food sources in Israel. A dataset including 192,340 test results for the detection of NTS contamination in food products in Israel between 2007 and 2021 was analyzed. Food samples were collected as part of routine testing and targeted programs for NTS detection from different facilities, such as food factories and slaughterhouses. The collected food samples included: non-thermally treated (raw) and mainly thermally treated ready-to-eat (RTE) products. Data were summarized and associations between NTS detection and different covariates were estimated using either: (i) Poisson regression model; or (ii) ꭕ2-tests. The odds ratio (OR) or prevalence ratio and 95 % confidence intervals (CI95 %) were calculated. The number of food products tested for NTS identification and further serotype classification has declined in recent years. However, the percentage of NTS positive results increased over time, reaching 18.11 % positive samples by 2021. The risk for NTS contamination was significantly higher in raw vs. RTE products: OR (CI95 %) = 290.60 (239.39-352.76), p < 0.001. The percentage of samples found positive for NTS in RTE products varied between sources, yet remained below 0.49 % for each source. However, in raw products, the NTS prevalence ranged between 1.05 % and 35.03 %, with food products from the chicken source significantly more positively associated with NTS contamination in comparison beef, fish, pig and turkey sources. Imported food, and slaughterhouses had a significantly higher prevalence of NTS contamination compare to factories food hygiene testing. With certain facilities, within each category, demonstrating significantly higher contamination compared to others. Moreover, the ten most common serotypes reported in human infections throughout this period were mostly found in chicken and turkey sources. The identification of certain sources and facilities/importers/slaughterhouses which may pose higher risk for NTS contamination was possible despite the declining resources invested in sampling and classification of NTS isolates in recent years. Therefore, our study further emphasizes the potential and importance of establishing a real-time surveillance for better tracing of NTS contaminations in food sources to protect public health.

Dynamical modeling of Salmonellosis in humans and dairy cattle with temperature and pH effects

Approximately 20 million cases and 0.15 million human fatalities worldwide each year are caused by Salmonellosis. A mechanistic compartmental model based on ordinary differential equations is proposed to evaluate the effects of temperature and pH on the transmission dynamics of Salmonellosis. The transmission potential of the disease in areas with temperature and pH stresses is examined. The next-generation matrix method is applied to compute the temperature-pH-dependent reproduction number ℛPT. The dynamical regimes of the system are examined using Lyapunov stability theory and backward bifurcation analysis. The uncertainty and global sensitivity analysis are examined using the Latin Hypercube Sampling (LHS) and Partial Rank Correlation Coefficient (PRCC) methods. The numerical simulations of the proposed model under favorable and unfavorable temperatures are performed with a 95% confidence interval (CI) for the reliability assessment of the model parameters. The analysis shows that the ingestion rates of Salmonella enterica subsp. enterica serovar Typhimurium bacteria in humans and dairy cattle, human-to-human transmission rate, cattle-to-cattle transmission rate, human shedding rate, dairy cattle shedding rate, and the rate of producing contaminated dairy products are directly proportional to the number of infected humans and infected dairy cattle. The temperature ranges of 100C-200C and 300C-400C and pHs greater than 3.8 have a significant effect on the dynamics of Salmonellosis. In order to eliminate Salmonellosis, the study recommends treating natural water bodies using the recommended chemical disinfectants during summer seasons and in areas with temperature ranges of 100C-200C, cooking food at the hottest temperatures, and storing food at the lowest temperatures for all pHs.

Dynamic Serotype Distribution and Antimicrobial Resistance of Salmonella Isolates from 2019 to 2023 in Guizhou, China

Introduction

Salmonella, a leading cause of human infectious diarrhea diseases, foodborne illness, and zoonotic infections, poses a significant health burden.

Methods

A retrospective screening was performed to elucidate the serotype distribution and antimicrobial resistance of 933 human Salmonella isolates from nine cities (prefectures) in Guizhou province of southwestern China between 2019 and 2023 through slide agglutination and antimicrobial resistance testing.

Results

Fifty-four different serotypes were identified in this study, with S. Typhimurium (44.4%) and S. Enteritidis (20.7%) being the predominant serotypes, followed by S. London (3.1%), S. Derby (2.8%), and S. Rissen (2.0%). A total of 39 serotypes were reported for the first time in Guizhou province, and 121 isolates (13.0%) could not be classified. The diversity of Salmonella serotypes in Guizhou has increased from 8 in 2019 to 39 in 2023. In addition, the detection rate of S. Enteritidis showed a decreasing trend over time, while the detection rate of S. Typhimurium demonstrated an annual increase since 2020. For 933 isolates, a significant majority (94.0%) exhibited resistance to at least one class of antimicrobial agents. The highest resistance observed was to ampicillin (86.4%), followed by resistance to tetracycline (76.3%) and streptomycin (72.8%). Notably, we discovered that the resistance rate to colistin was 4.7%, with 93.2% of these isolates being S. Enteritidis. Meanwhile, 78.5% of isolates were demonstrated multidrug resistance (MDR), with the MDR rates for S. Rissen and S. Typhimurium exceeding 90%. Additionally, 5.7% of Salmonella isolates were extensively drug-resistant (XDR), with S. Typhimurium and S. Enteritidis exhibiting XDR rates of 5.1% and 4.1%, respectively. The rate of MDR and XDR in Salmonella peaked in 2019 and then gradually declined from 2020 to 2022, rising again in 2023.

Conclusion

Our research revealed an increasing diversity in Salmonella serotypes within Guizhou province, alongside significant challenges posed by MDR and a rising XDR rate. Therefore, it is essential to continuously improve the surveillance of Salmonella, keep track of changes in serotype distribution and dynamic shifts, and strengthen the persistent monitoring of antimicrobial agents.

Detection of Salmonella by competitive ELISA of lipopolysaccharide secreted into the culture medium

Detection of Salmonella in food is topical due to known cases of salmonellosis epidemics. Immunochemical methods including ELISA are widely used for Salmonella detection. Traditionally, commercial ELISA kits are based on sandwich technique and detect lipopolysaccharide (LPS), which is considered to be the component of the outer membrane of Gram-negative bacteria. Our aim was elaboration of competitive ELISA test for Salmonella detection in food with improved parameters. It was shown that in the Salmonella culture after the standard sample preparation procedure LPS is present mainly outside cells as a component of outer membrane vesicles. Improved sample preparation procedure includes separation of bacteria from the medium and analysis of the medium, which increases analytical sensitivity. Immobilization of the bovine serum albumin (BSA)-LPS conjugate in microplate wells allows to obtain a more homogeneous coating than immobilization of LPS itself. Thus, we have developed test system for Salmonella detection in food by competitive ELISA of LPS secreted into the culture medium with the immobilized BSA-LPS conjugate and monoclonal antibodies (mAb) to LPS core in the liquid phase. New competitive ELISA test is high sensitive, give reproducible results, allows the detection of any Salmonella serotype and is important for the protection of human health.

In Silico Detection of Integrons and Their Relationship with Resistance Phenotype of Salmonella Isolates from a Brazilian Pork Production Chain

The pork production chain is an important reservoir of antimicrobial resistant bacteria. This study identified and characterized integrons in Salmonella isolates from a Brazilian pork production chain and associate them with their antibiotic resistance pattern. A total of 41 whole-genome sequencing data of nontyphoidal Salmonella were analyzed using PlasmidSPAdes and IntegronFinder software. Nine isolates (21.9%) had some integrons identified (complete and/or incomplete). Six complete class 1 integrons were found, with streptomycin resistance genes (aadA1, aadA2) alone or downstream of a trimethoprim resistance gene (dfrA1, dfrA12), and some also containing resistance genes for sulfonamides (sul1, sul3) and chloramphenicol (cmlA1). Class 2 integron was detected in only one isolate, containing dfrA1-sat2-aadA1 gene cassettes. Five isolates harbored CALINs-clusters attC but lacking integrases-with antimicrobial resistance genes typically found in integron structures. In all, integrons were observed among four serotypes: Derby, Bredeney, Panama, and monophasic var. Typhimurium I 4,[5],12:i:-. The association of integrons with antibiotic resistance phenotype showed that these elements were predominantly identified in multidrug resistance isolates, and six of the seven gentamicin-resistant isolates had integrons. So, surveillance of integrons in Salmonella should be performed to identify the potential for the spread of antimicrobial resistance genes among bacteria.

Salmonella Infection in Poultry: A Review on the Pathogen and Control Strategies

Salmonella is the leading cause of food-borne zoonotic disease worldwide. Non-typhoidal Salmonella serotypes are the primary etiological agents associated with salmonellosis in poultry. Contaminated poultry eggs and meat products are the major sources of human Salmonella infection. Horizontal and vertical transmission are the primary routes of infection in chickens. The principal virulence genes linked to Salmonella pathogenesis in poultry are located in Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2). Cell-mediated and humoral immune responses are involved in the defense against Salmonella invasion in poultry. Vaccination of chickens and supplementation of feed additives like prebiotics, probiotics, postbiotics, synbiotics, and bacteriophages are currently being used to mitigate the Salmonella load in poultry. Despite the existence of various control measures, there is still a need for a broad, safe, and well-defined strategy that can confer long-term protection from Salmonella in poultry flocks. This review examines the current knowledge on the etiology, transmission, cell wall structure, nomenclature, pathogenesis, immune response, and efficacy of preventative approaches to Salmonella.

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.

Non-Antibiotics Strategies to Control Salmonella Infection in Poultry

Salmonella spp. is a facultative intracellular pathogen causing localized or systemic infections, involving economic and public health significance, and remains the leading pathogen of food safety concern worldwide, with poultry being the primary transmission vector. Antibiotics have been the main strategy for Salmonella control for many years, which has allowed producers to improve the growth and health of food-producing animals. However, the utilization of antibiotics has been reconsidered since bacterial pathogens have established and shared a variety of antibiotic resistance mechanisms that can quickly increase within microbial communities. The use of alternatives to antibiotics has been recommended and successfully applied in many countries, leading to the core aim of this review, focused on (1) describing the importance of Salmonella infection in poultry and the effects associated with the use of antibiotics for disease control; (2) discussing the use of feeding-based (prebiotics, probiotics, bacterial subproducts, phytobiotics) and non-feeding-based (bacteriophages, in ovo injection, vaccines) strategies in poultry production for Salmonella control; and (3) exploring the use of complementary strategies, highlighting those based on -omics tools, to assess the effects of using the available antibiotic-free alternatives and their role in lowering dependency on the existing antimicrobial substances to manage bacterial infections in poultry effectively.

Salmonella Typhimurium ST313 isolated in Brazil revealed to be more invasive and inflammatory in murine colon compared to ST19 strains

Salmonella Typhimurium (ST313) has caused an epidemic of invasive disease in sub-Saharan Africa and has been recently identified in Brazil. As the virulence of this ST is poorly understood, the present study aimed to (i) perform the RNA-seq in vitro of S. Typhimurium STm30 (ST313) grown in Luria-Bertani medium at 37°C; (ii) compare it with the RNA-seq of the S. Typhimurium SL1344 (ST19) and S. Typhimurium STm11 (ST19) strains under the same growing conditions; and (iii) examine the colonization capacity and expression of virulence genes and cytokines in murine colon. The STm30 (ST313) strain exhibited stronger virulence and was associated with a more inflammatory profile than the strains SL1344 (ST19) and STm11 (ST19), as demonstrated by transcriptome and in vivo assay. The expression levels of the hilA, sopD2, pipB, and ssaS virulence genes, other Salmonella pathogenicity islands SPI-1 and SPI-2 genes or effectors, and genes of the cytokines IL-1β, IFN-γ, TNF-α, IL-6, IL-17, IL-22, and IL-12 were increased during ST313 infection in C57BL/6J mice. In conclusion, S. Typhimurium STm30 (ST313) isolated from human feces in Brazil express higher levels of pathogenesis-related genes at 37°C and has stronger colonization and invasion capacity in murine colon due to its high expression levels of virulence genes, when compared with the S. Typhimurium SL1344 (ST19) and STm11 (ST19) strains. STm30 (ST313) also induces stronger expression of pro-inflammatory cytokines in this organ, suggesting that it causes more extensive tissue damage.

Changing Patterns of Salmonella enterica Serovar Rissen From Humans, Food Animals, and Animal-Derived Foods in China, 1995-2019

Salmonellosis represents a growing threat to global public health. Salmonella enterica remains the leading cause of bacterial foodborne diseases in China. Salmonella enterica serovar Rissen (S. Rissen) has been recognized as one of the emerging serovars among humans in different countries worldwide. However, knowledge on the prevalence of S. Rissen in China is largely lacking. To address essential epidemiological information for S. Rissen in China, a total of 1,182 S. Rissen isolates recovered from samples across the food chain were collected from 16 provinces or province-level cities between 1995 and 2019. Risk factors due to the consumption of animal-derived food products were also analyzed. We found S. Rissen is widely distributed, especially in the Eastern and Southern parts of China, and there is an increasing frequency in recent years as evidenced by the greater number of isolates recovered in 2016, 2017, and 2018. Interestingly, the majority of S. Rissen isolates recovered in this study were from human samples (63.4%; 749/1182), remarkably, 58.4% (438/749) were from asymptomatic carriers. We obtained most of the S. Rissen isolates from humans from Guangxi (59.5%; 446/749) and Shanghai (29.5%; 221/749). Among 302 human diarrheal isolates (40.3%; 302/749), we found 44.6% (139/311) of S. Rissen in children with diarrhea (age below 10 years old). This is of clinical significance as diarrhea is one of the crucial causes of child mortality globally and our findings here highlighted the importance of Salmonella infections in Chinese children. Additionally, S. Rissen isolates were also found to be associated with pork and poultry products in China. This study projected the most updated national-wide study of S. Rissen isolates obtained from different sources in China over the past two decades. Continued surveillance is warranted to further monitor this emerging serovar in China and elsewhere over the world.

Salmonella Bacterin Vaccination Decreases Shedding and Colonization of Salmonella Typhimurium in Pigs

Since the occurrence of swine salmonellosis has increased over time and control strategies other than biosecurity are highly recommended, the present study aimed to evaluate the efficacy of vaccination with Salmonella Choleraesuis and Salmonella Typhimurium bacterins in pigs. Two experimental groups were formed: G1, animals immunized with two doses of a commercial vaccine (n = 20); G2, control group (n = 20). After vaccination, all pigs were orally challenged (D0) with 10⁸ CFU of Salmonella Typhimurium and evaluated for 40 days. Every 10 days after D0, five piglets from each experimental group were euthanized and submitted to the necroscopic examination, when organ samples were collected. Blood samples and rectal swabs were collected before the first dose of the vaccine (D−42), before the second dose (D−21), before the challenge (D0), and thereafter, every three days until D39. Blood count, serum IgG measurement by ELISA, and the excretion of Salmonella Typhimurium in feces were evaluated. While the results from blood count and serum IgG concentration did not differ, the detection and excretion of Salmonella between G1 and G2 differed (p < 0.05). Therefore, it was observed that this vaccine partially protected the animals against experimental infection with Salmonella Typhimurium, reducing the excretion of bacteria in feces.

Comparative Analysis Using Pulsed-Field Gel Electrophoresis Highlights a Potential Transmission of Salmonella Between Asymptomatic Buffaloes and Pigs in a Single Farm

Buffaloes and pigs play an important epidemiological roll in the Salmonella infection cycle, and asymptomatic animals can act as key component in the dissemination of the disease by horizontal, vertical, and cross-species transmission. Our study aimed and was able to confirm evidences of a cross-species transmission of Salmonella Agona between asymptomatic buffaloes and pigs. Also, we described Salmonella infection within the pig production phases, involving serotypes Agona, Senftenberg and Schwarzengrund. Rectal samples were collected from Jafarabadi buffaloes (n = 25) and Piau pigs (n = 32), located on a single farm. Salmonella Agona was isolated from lactating buffaloes, gilts, pregnant sows, and weaned pigs, Salmonella Schwarzengrund from lactating sows and Salmonella Senftenberg from gilts, pregnant sows, lactating sows, and weaned pigs. Pulsed-field Gel Electrophoresis protocol (PFGE) was performed and revealed four different profiles. Profile 1 (Salmonella Agona), isolated from a pregnant sow, a gilt and two lactating buffaloes, revealed a indistinguishable PFGE pattern, confirming evidences of potential cross-species transmission. Profile 2 (Salmonella Agona), 3 (Salmonella Senftenberg), and 4 (Salmonella Schwarzengrund), isolated from pigs, revealed important indistinguishable PFGE patterns, evidencing Salmonella infection within the pig production phases. Considering the epidemiological relevance of buffaloes and pigs in the cycle of Salmonella infection, confirmation of a potential cross-species transmission of Salmonella Agona and potential Salmonella infection within the pig production phases highlights the importance of the correct establishment of preventive health strategies in farms, in special the importance of avoiding contact between buffaloes and pigs, since cross-species transmission can occur, increasing the risk of spreading the disease.

Salmonella spp. in Wild Free-Living Birds from Atlantic Forest Fragments in Southern Bahia, Brazil

Wild animals have an ecological function and can serve as sentinels to identify infectious agents and as indicators of environmental health. Among the zoonotic pathogens, Salmonella spp. deserve special attention due to their high worldwide prevalence and their ubiquity of hosts. With the aim of investigating the presence of Salmonella spp. in wild birds from the Atlantic Forest in southern Bahia, Brazil, we collected 114 fecal samples of wild birds (14 families) between 2016 and 2017. Fecal samples were collected by means of cloacal swab and subjected to microbiological culture to isolate and serotype Salmonella spp. specifically. Antibiotic susceptibility was determined using the disk diffusion test protocol. Only one bird, Ceratopipra rubrocapilla, tested positive for Salmonella enterica subsp. enterica serotype Agona, which is the first record for this bird species. This isolate exhibited intermediate sensitivity to amikacin and gentamicin and sensitivity to the other 13 antibiotics tested. Results may indicate environmental preservation since the studied areas had minimal human activity and good sanitary quality. Despite the low prevalence, it is necessary to monitor wildlife and establish disease control and surveillance systems, especially for zoonotic diseases.

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.

Non-typhoidal Salmonella in the Pig Production Chain: A Comprehensive Analysis of Its Impact on Human Health

Salmonellosis remains one of the most frequent foodborne zoonosis, constituting a worldwide major public health concern. The most frequent sources of human infections are food products of animal origin, being pork meat one of the most relevant. Currently, particular pig food production well-adapted and persistent Salmonella enterica serotypes (e.g., Salmonella Typhimurium, Salmonella 1,4,[5],12:i:-, Salmonella Derby and Salmonella Rissen) are frequently reported associated with human infections in diverse industrialized countries. The dissemination of those clinically-relevant Salmonella serotypes/clones has been related to the intensification of pig production chain and to an increase in the international trade of pigs and pork meat. Those changes that occurred over the years along the food chain may act as food chain drivers leading to new problems and challenges, compromising the successful control of Salmonella. Among those, the emergence of antibiotic resistance in non-typhoidal Salmonella associated with antimicrobials use in the pig production chain is of special concern for public health. The transmission of pig-related multidrug-resistant Salmonella serotypes, clones and/or genetic elements carrying clinically-relevant antibiotic resistance genes, frequently associated with metal tolerance genes, from pigs and pork meat to humans, has been reported and highlights the contribution of different drivers to the antibiotic resistance burden. Gathered data strengthen the need for global mandatory interventions and strategies for effective Salmonella control and surveillance across the pig production chain. The purpose of this review was to provide an overview of the role of pig and pork meat in human salmonellosis at a global scale, highlighting the main factors contributing to the persistence and dissemination of clinically-relevant pig-related Salmonella serotypes and clones.