Review of egg-related salmonellosis and reduction strategies in United States, Australia, United Kingdom and New Zealand

Internal Organ Colonization by Salmonella Enteritidis in Layer Pullets Infected at Two Different Ages During Rearing in Cage-Free Housing

The poultry-housing environment plays a significant role in the transmission and persistence of the egg-associated pathogen Salmonella Enteritidis in laying flocks. The commercial egg industry is in the midst of a transition toward cage-free housing, but the food safety ramifications of this shift are not yet certain. The present study assessed internal organ colonization by Salmonella Enteritidis in layer pullets reared in cage-free housing and infected at two different ages. Groups of 280 pullets were transferred from the rearing facility (at 9 wk of age in one trial and 15 wk in another) to a containment facility with four isolation rooms simulating commercial cage-free barns with perches and nest boxes (70 birds/room). Twenty-four pullets in each room were orally inoculated with Salmonella Enteritidis immediately after placement in the containment facility. At 1-2 wk postinoculation in each trial, samples of liver, spleen, and intestinal tract were collected from all birds in two rooms for bacteriologic culturing to detect Salmonella Enteritidis. At 21-22 wk of age, samples of spleen, ovary, and intestinal tract were similarly collected and tested from all birds in the remaining two rooms. Among samples collected at 1-2 wk postinoculation, Salmonella Enteritidis was isolated significantly more often from groups of pullets infected initially at 15 wk of age than from those infected at 9 wk (61% vs. 38% of livers, 59% vs. 31% of spleens, and 84% vs. 57% of intestines). Among samples collected at 21-22 wk of age, the frequency of recovery of Salmonella Enteritidis was again significantly greater in birds infected at 15 wk of age than in those infected at 9 wk (16% vs. 6% of spleens, 9% vs. 1% of ovaries, and 26% vs. 10% of intestines). These data suggest that Salmonella Enteritidis infections introduced into flocks during the later stages of pullet rearing have greater potential to persist into the early phase of egg production.

Emergence of tet(X4)-positive Enterobacterales in retail eggs and the widespread of IncFIA(HI1)-HI1A-HI1B(R27) plasmids carrying tet(X4)

The proliferation of antimicrobial-resistant microbes and resistance genes in various foods poses a serious hazard to public health. The plasmid-mediated tigecycline resistance gene tet(X4) has been detected in Enterobacterales from various niches but has not yet been reported in eggs. This study aimed to investigate the occurrence and characteristics of tigecycline-resistant strains from retail eggs. A total of 144 eggs were purchased from farmers' markets in Guangdong province, China, and eggshell (n = 144) and egg content (n = 96) samples were used to screen for tigecycline-resistant strains. Eight Escherichia coli strains (two ST195, one ST48, ST8165, ST752, ST93, ST189, and ST224) and one Klebsiella pneumoniae strain (ST252) recovered from eight (5.56 %, 8/144) egg samples (eggshells, n = 6; egg content, n = 2) were positive for tet(X4). Notably, the two E. coli ST195 strains were closely (15-54 SNPs) related to all the tet(X4)-positive E. coli ST195 from various origins (food animals, foods, migratory birds, human, and environment) deposited in GenBank. The E. coli ST224 showed a close phylogenetic relationship (9-12 SNPs) with two tet(X4)-positive E. coli strains from chicken feces and retail chicken in Guangdong province. The hybrid plasmid IncFIA(HI1)-HI1A-HI1B(R27) constitutes the predominant tet(X4) vector both herein (7/9, 77.78 %) and in the GenBank database (32/160, 20 %). The tet(X4)-positive IncFIA(HI1)-HI1A-HI1B(R27) plasmids, sharing highly similar structures, have been widely disseminated across China. However, the IncFIA(HI1)-HI1A-HI1B(R27) plasmids exhibit poor stability and low conjugation frequency. The contamination of tet(X4)-positive bacteria internally and externally in retail eggs poses a prospective food safety threat. More attention should be paid to the spread of the tet(X4) gene via epidemic clone E. coli ST195 and the plasmid IncFIA(HI1)-HI1A-HI1B(R27).

Effect of the storage temperature on the quality of eggs inoculated with Salmonella Enteritidis onto shell

This study explored the temperature-dependent effect on the growth characteristics of Salmonella Enteritidis (SE) on eggshell toward identifying an appropriate storage temperature for unwashed eggs in an actual distribution environment. Among the test storage temperatures (10 °C, 25 °C, and 35 °C), 25 °C was determined to be an appropriate storage temperature, with no effect of changing temperature on the control of SE on eggshell. Regarding the effect of the temperature on egg quality, the quality indicators of egg such as Haugh unit, yolk index, albumin index, and albumin pH were significantly maintained. These results indicated that unwashed eggs should be distributed at 25 °C for SE control, and the storage temperature should be below 10 °C from at least day 4 onward after the start of distribution to maintain egg quality. This study will assist for safety management of unwashed egg in an actual distribution environment.

Gene expression response to Salmonella Typhimurium in the cecal tonsil reveals a potential mechanism of resistance in chickens

Salmonella has been one of the most important factors restricting the development of the poultry industry and also poses great threat to public health. To get insight into molecular alterations that occur during bacterial infection, we sequenced the cecal tonsil transcriptome in 2 chicken breeds (Beijing-You and Cobb) known to have differing resistance to Salmonella. The 28-day-old chickens were orally challenged by 1.83 × 1011 CFU Salmonella Typhimurium, and the cecal tonsil transcriptome was sequenced 3 d postinfection. Analysis identified 201 and 170 differentially expressed genes response to Salmonella in 2 chicken breeds, respectively. They were involved in the Toll-like receptor signaling pathway and activated the production of pro-inflammatory cytokines and chemokines. The protein-protein interaction (PPI) network suggested MMP9 as a crucial protein that may be involved in extracellular matrix breakdown and leukocyte migration in the resistant breed (Beijing-You). Meanwhile, in susceptible chickens (Cobb), ACOD1 was the key gene in the PPI network and might promote the expression of genes related to oxidative stress response and gastrointestinal tract function. These findings provide insight into the differing resistance of these 2 chicken breeds.

A Review on Microbiological Source Attribution Methods of Human Salmonellosis: From Subtyping to Whole-Genome Sequencing

Salmonella is one of the main causes of human foodborne illness. It is endemic worldwide, with different animals and animal-based food products as reservoirs and vehicles of infection. Identifying animal reservoirs and potential transmission pathways of Salmonella is essential for prevention and control. There are many approaches for source attribution, each using different statistical models and data streams. Some aim to identify the animal reservoir, while others aim to determine the point at which exposure occurred. With the advance of whole-genome sequencing (WGS) technologies, new source attribution models will greatly benefit from the discriminating power gained with WGS. This review discusses some key source attribution methods and their mathematical and statistical tools. We also highlight recent studies utilizing WGS for source attribution and discuss open questions and challenges in developing new WGS methods. We aim to provide a better understanding of the current state of these methodologies with application to Salmonella and other foodborne pathogens that are common sources of illness in the poultry and human sectors.

The aroA and luxS Double-Gene Mutant Strain Has Potential to Be a Live Attenuated Vaccine against Salmonella Typhimurium

Salmonella Typhimurium (S. Typhimurium) is a zoonotic pathogen posing a threat to animal husbandry and public health. Due to the emergence of antibiotic-resistant strains, alternative prevention and control strategies are needed. Live attenuated vaccines are an ideal option that provide protection against an S. Typhimurium pandemic. To develop a safe and effective vaccine, double-gene mutations are recommended to attenuate virulence. In this study, we chose aroA and luxS genes, whose deletion significantly attenuates S. Typhimurium's virulence and enhances immunogenicity, to construct the double-gene mutant vaccine strain SAT52ΔaroAΔluxS. The results show that the mutant strain's growth rate, adherence and invasion of susceptible cells are comparable to a wild-type strain, but the intracellular survival, virulence and host persistence are significantly attenuated. Immunization assay showed that 106 colony-forming units (CFUs) of SAT52ΔaroAΔluxS conferred 100% protection against wild-type challenges; the bacteria persistence in liver and spleen were significantly reduced, and no obvious pathological lesions were observed. Therefore, the double-gene mutant strain SAT52ΔaroAΔluxS exhibits potential as a live attenuated vaccine candidate against S. Typhimurium infection.

Salmonella in eggs and egg-laying chickens: pathways to effective control

Eggs contaminated with Salmonella have been internationally significant sources of human illness for several decades. Most egg-associated illness has been attributed to Salmonella serovar Enteritidis, but a few other serovars (notably S. Heidelberg and S. Typhimurium) are also sometimes implicated. The edible interior contents of eggs typically become contaminated with S. Enteritidis because the pathogen's unique virulence attributes enable it to colonize reproductive tissues in systemically infected laying hens. Other serovars are more commonly associated with surface contamination of eggshells. Both research and field experience have demonstrated that the most effective overall Salmonella control strategy in commercial laying flocks is the application of multiple interventions throughout the egg production cycle. At the preharvest (egg production) level, intervention options of demonstrated efficacy include vaccination and gastrointestinal colonization control via treatments such as prebiotics, probiotics, and bacteriophages, Effective environmental management of housing systems used for commercial laying flocks is also essential for minimizing opportunities for the introduction, transmission, and persistence of Salmonella in laying flocks. At the postharvest (egg processing and handling) level, careful regulation of egg storage temperatures is critical for limiting Salmonella multiplication inside the interior contents.

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.

Comparative Evaluation of Egg Quality in Response to Temperature Variability: From Farm to Table Exposure Scenarios

This study aimed to develop appropriate temperature management practices and provide scientific evidence to support the development of sell-by-date guidance for eggs. Washed and unwashed eggs were subjected to storage under six different scenarios, and both types of eggs were stored at temperatures up to 35°C to evaluate the sell-by-date. Despite temperature fluctuations or continuous storage at 30°C for 5 days, subsequent storage at 10°C resulted in significantly higher Haugh unit and yolk index on day 15. These results indicate that refrigerating eggs from retail sales until consumption is effective for egg quality management, despite the exposure of up to 35°C during distribution. In terms of sell-by-date evaluation, washed eggs retained class B quality for an additional 37 days beyond the recommended sell-by-date at 15°C, which is above the regulated storage temperature. However, unwashed eggs maintained class B quality for approximately 20 days at 30°C-35°C, emphasizing the need for sell-by-date guidelines for unwashed eggs. This study is the first to provide appropriate egg-handling practices based on the actual distribution environment in Korea.

Quercetin Alleviates Inflammation and Energy Deficiency Induced by Lipopolysaccharide in Chicken Embryos

Energy deficiency causes multiple organ dysfunctions after LPS induction. Quercetin is a phenolic compound found in herbal medicines. However, the effects of quercetin in alleviating LPS-induced energy deficiency remain unclear. In the present study, an in vivo LPS-induced inflammation model was established in chicken embryos. Specific pathogen-free chicken embryos (n = 120) were allocated to control, PBS with or without ethanol, quercetin (10, 20, or 40 nmol, respectively), and LPS (125 ng/egg) with or without quercetin groups. Fifteen day old embryonated eggs were injected with the abovementioned solutions via the allantoic cavity. On embryonic day 19, the tissues of the embryos were collected for histopathological examination using frozen oil red O staining, RNA extraction, real-time quantitative polymerase chain reaction, and immunohistochemical investigations. The glycogen and lipid contents in the liver increased after LPS stimulation as compared with the PBS group, whereas quercetin decreased the accumulation as compared with the LPS group. The mRNA expressions of AMPKα1 and AMPKα2 in the duodena, ceca, and livers were upregulated after LPS induction as compared with the PBS group, while quercetin could downregulate these expressions as compared with the LPS group. The immunopositivity of AMPKα2 in the villus, crypt, lamina propria, tunica muscularis, and myenteric plexus in the duodena and in the cytoplasms of hepatocytes significantly increased after LPS induction when compared with the PBS group (p < 0.01), whereas the immunopositivity to AMPKα2 in the quercetin treatment group significantly decreased when compared with the LPS group (p < 0.01 or p < 0.05). The LPS-induced high expressions of transcription factor PPARα and glucose transporter (SGLT1) were blocked by quercetin in the duodena, ceca, and livers. Quercetin treatment improved the LPS-induced decrease in APOA4 in the duodena, ceca, and livers. The mRNA expression of PEPT1 in the duodena and ceca increased after LPS challenge, whereas quercetin could downregulate PEPT1 gene expression. These data demonstrate that quercetin improved the energy deficiency induced by LPS in chicken embryos. The LPS-induced inflammation model was established to avoid the effect of LPS exposure from the environment and intestinal flora. The results form the basis the administration of quercetin pretreatment (in ovo infection) to improve the energy state of chicken embryos and improve the inflammation response.

A review on circular RNAs and bacterial infections

Bacterial infections and related diseases have been a major burden on social public health and economic stability around the world. However, the effective diagnostic methods and therapeutic approaches to treat bacterial infections are still limited. As a group of non-coding RNA, circular RNAs (circRNAs) that were expressed specifically in host cells and played a key regulatory role have the potential to be of diagnostic and therapeutic value. In this review, we systematically summarize the role of circRNAs in common bacterial infections and their potential roles as diagnostic markers and therapeutic targets.

Effects of Salmonella Enteritidis infection on TLRs gene expression and microbial diversity in cecum of laying hens

Salmonella Enteritidis (SE) is an important foodborne pathogen primarily causing human disease through contaminated food and water. In the current study, to assess the effect of Salmonella Enteritidis infection on the immune system and the microbial diversity of cecum and oviduct in chickens, twelve 24-week-old SE-negative White Leghorn layers were randomly selected and divided into 2 groups. Chickens in the challenge group were orally inoculated with SE, and chickens in the control group received an equal amount of sterilized Phosphate Buffered Saline solution. Serum and tissue samples (cecum, oviduct, ovary, liver, spleen, and pancreas) were collected at 7 days and 14 days post-infection (dpi). Quantitative PCR was used to detect the expression of Toll-like receptors (TLRs) in the cecum, oviduct and ovary. To understand the influence of SE infection on the microbial profile of the cecum and oviduct, microbial community composition of the cecal contents and oviducal contents were analyzed through 16S rRNA sequencing. Results showed that SE infection caused damage to the digestive organs, reproductive organs, and immune organs in laying hens. The expression of TLR1a, TLR1b, TLR2, TLR4, TLR5, TLR7 and TLR15 in the cecum were induced, and the content of IFN-γ, TNF-α, IL-2 and IL-18 in serum increased after SE infection. The composition of the microbial community significantly changed in cecal content, the dominant phylum of Firmicutes increased, and Bacteroidetes decreased significantly. In the oviduct, the microbial diversity became complicated, the dominant bacteria Faecalibacterium was significantly increased, and Bacteroides was significantly decreased. This study investigated the effects of SE infection in laying hens, including host innate immunity, the expression of TLRs, and changes in the composition of microbes in the cecum and reproductive tract. Our results may provide a scientific basis for the Salmonella Enteritidis control in chicken, the maintenance of oviduct function, and the guarantee of clean egg production.

Genomes-based MLST, cgMLST, wgMLST and SNP analysis of Salmonella Typhimurium from animals and humans

Salmonella Typhimurium (S. Typhimurium) is an important food-borne and zoonotic pathogen that causes salmonellosis. With the development of whole genome sequencing (WGS), genome-based typing has been widely applied to bacteriology. In this study, we investigated genotyping and phylogenetic clusters of S. Typhimurium isolates from humans and animals in different provinces (including Beijing, Shandong, Guangxi, Shaanxi, Henan, and Shanghai) of China during 2009-2018 using multi locus sequence typing (MLST), core genome MLST (cgMLST), whole genome MLST (wgMLST) and single nucleotide polymorphism (SNP) based on WGS. 29 S. Typhimurium isolates from chicken (n = 22), sick pigeon (n = 2), patients (n = 4) and sick swine (n = 1) were tested. MLST analysis showed S. Typhimurium strains were divided into four STs, namely ST19 (n = 14), ST34 (n = 12), ST128 (n = 2) and ST1544 (n = 1). cgMLST and wgMLST divided 29 strains into 27 cgSTs and 29 wgST, respectively. Phylogenetic clustering showed that all isolates were divided into 4 clusters and 4 singletons. SNP analysis was used to examine MLST, cgMLST, wgMLST analysis. Finally, comparisons of MLST, cgMLST, wgMLST, and SNP were analyzed and the results showed their precision increased in order. In summary, genomic typing and phylogenetic relationships of 29 S. Typhimurium strains from different sources in China were analyzed. These findings were beneficial to investigate molecular pathogenesis, bacterial diversity, and traceability analysis of Salmonella.

Salmonella Enteritidis RfbD enhances bacterial colonization and virulence through inhibiting autophagy

Autophagy is a crucial innate immune response that clears pathogens intracellularly. Salmonella enterica serovar Enteritidis (S.E) has emerged as one of the most important food-borne pathogens. Here, we reported that dTDP-4-dehydro-β-ւ-rhamnose reductase (RfbD) was able to enhance bacterial colonization in vivo and in vitro by regulating autophagy. We screened the transposon mutant library of Salmonella Enteritidis strain Z11 by High-Content Analysis System, found that rfbD gene has an effect on autophagy. The Z11ΔrfbD-infected group showed greater expression of LC3-II than the Z11-infected group in HeLa, RAW264.7, and J774A.1 cells. Overall, the survival of Z11ΔrfbD in RAW264.7 cells was reduced after 8 h of infection compared to that of the Z11 wild-type strain. In addition, we observed that inhibition of autophagic flux significantly increased the survival of Z11ΔrfbD in RAW264.7 cells. Mice infection experiments revealed that Z11ΔrfbD virulence was significantly reduced, and bacterial load was reduced in the liver and cecum in mice model, and LC3-II expression was significantly increased. These findings indicate an important role of Salmonella Enteritidis protein as a strategy to suppress autophagy and provides new ideas for manipulating autophagy as a novel strategy to treat infectious diseases.

Development of a Dual Mode UCNPs-MB Biosensor in Combination with PCR for Sensitive Detection of Salmonella

In recent years, the high prevalence of Salmonella has emerged as a serious threat to public safety, prompting attempts to utilize accurate, rapid, and direct methods to ensure food safety. In this study, a multifunctional platform featuring dual-mode detection channels (colorimetric-fluorescence) combined with polymer chain reaction (PCR) was proposed for the sensitive and rapid detection of Salmonella. Additionally, the colorimetric measurements were achieved by color changes induced by methylene blue (MB) insertion into the double-stranded DNA, and the fluorescence measurements were performed by internal filter effect (IFE)-induced fluorescence quenching of upconversion nanoparticles (UCNPs) by MB. The results showed that the IFE and PCR amplification processes improved the sensitivity of the sensor towards Salmonella detection, with a limit of detection (LOD) of 21.8 CFU/mL. Moreover, this colorimetric-fluorescence dual-mode PCR biosensor was applied to determine Salmonella in food samples, such as chicken, egg, and fish, which produced satisfactory results. Overall, the present study results demonstrate the potential for combining PCR amplification with IFE to develop an efficient and reliable dual-mode analysis platform to safeguard food security.

Effect of a Saccharomyces cerevisiae Postbiotic Feed Additive on Salmonella Enteritidis Colonization of Cecal and Ovarian Tissues in Directly Challenged and Horizontally Exposed Layer Pullets

Determining the efficacy of feed-additive technologies utilized as pre-harvest food-safety interventions against Salmonella enterica may be influenced by factors including, but not limited to, mechanism of action, experimental design variables, Salmonella serovar(s), exposure dose, route, or duration in both controlled research and real-world field observations. The purpose of this study was to evaluate the dietary inclusion of a Saccharomyces cerevisiae fermentation-derived postbiotic (SCFP) additive (Diamond V, Original XPC®) on the colonization of cecal and ovarian tissues of commercial pullets directly and indirectly exposed to Salmonella Enteritidis (SE). Four hundred and eighty commercial, day-of-age W-36 chicks were randomly allotted to 60 cages per treatment in two identical BSL-2 isolation rooms (Iowa State University) with four birds per cage and fed control (CON) or treatment (TRT) diets for the duration of study. At 16 weeks, two birds per cage were directly challenged via oral gavage with 1.1 × 109 CFU of a nalidixic-acid-resistant SE strain. The remaining two birds in each cage were thus horizontally exposed to the SE challenge. At 3, 7, and 14 days post-challenge (DPC), 20 cages per group were harvested and sampled for SE prevalence and load. No significant differences were observed between groups for SE prevalence in the ceca or ovary tissues of directly challenged birds. For the indirectly exposed cohort, SE cecal prevalence at 7 DPC was significantly lower for TRT (50.0%) vs. CON (72.5%) (p = 0.037) and, likewise, demonstrated significantly lower mean SE cecal load (1.69 Log10) vs. CON (2.83 Log10) (p = 0.005). At 14 DPC, no significant differences were detected but ~10% fewer birds remained positive in the TRT group vs. CON (p > 0.05). These findings suggest that diets supplemented with SCFP postbiotic may be a useful tool for mitigating SE colonization in horizontally exposed pullets and may support pre-harvest food-safety strategies.

Comparison of Antimicrobial Resistance among Commensal Escherichia coli Isolated from Retail Table Eggs Produced by Laying Hens from the Cage and Non-Cage Housing Systems in Western Australia

Antimicrobial resistance (AMR) has become a global public health concern in recent decades. Although several investigations evaluated AMR in commensal and pathogenic bacteria from different foods of animal origin in Australia, there is a lack of studies that compared AMR in commensal E. coli isolated from retail table eggs obtained from different laying hen housing systems. This study aimed to determine AMR and differences in AMR patterns among E. coli isolates recovered from retail table eggs sourced from caged and non-caged housing systems in Western Australia. Commensal E. coli isolates were tested for susceptibility to 14 antimicrobials using a broth microdilution method. Clustering analyses and logistic regression models were applied to identify patterns and differences in AMR. Overall, there were moderate to high frequencies of resistance to the antimicrobials of lower importance used in Australian human medicine (tetracycline, ampicillin, trimethoprim, and sulfamethoxazole) in the isolates sourced from the eggs of two production systems. All E. coli isolates were susceptible to all critically important antimicrobials except the very low level of resistance to ciprofloxacin. E. coli isolates from eggs of non-caged systems had higher odds of resistance to tetracycline (OR = 5.76, p < 0.001) and ampicillin (OR = 3.42, p ≤ 0.01) compared to the isolates from eggs of caged systems. Moreover, the number of antimicrobials to which an E. coli isolate was resistant was significantly higher in table eggs from non-caged systems than isolates from caged systems’ eggs. Considering the conservative approach in using antimicrobials in the Australian layer flocks, our findings highlight the potential role of the environment or human-related factors in the dissemination and emergence of AMR in commensal E. coli, particularly in retail table eggs of non-cage system origin. Further comprehensive epidemiological studies are required to better understand the role of different egg production systems in the emergence and dissemination of AMR in commensal E. coli.

Genomic Epidemiology and Multilevel Genome Typing of Australian Salmonella enterica Serovar Enteritidis

Salmonella enterica serovar Enteritidis is one of the leading causes of salmonellosis in Australia. In this study, a total of 568 S. Enteritidis isolates from two Australian states across two consecutive years were analyzed and compared to international strains, using the S. Enteritidis multilevel genome typing (MGT) database, which contained 40,390 publicly available genomes from 99 countries. The Australian S. Enteritidis isolates were divided into three phylogenetic clades (A, B, and C). Clades A and C represented 16.4% and 3.5% of the total isolates, respectively, and were of local origin. Clade B accounted for 80.1% of the isolates which belonged to seven previously defined lineages but was dominated by the global epidemic lineage. At the MGT5 level, three out of five top sequence types (STs) in Australia were also top STs in Asia, suggesting that a fair proportion of Australian S. Enteritidis cases may be epidemiologically linked with Asian strains. In 2018, a large egg-associated local outbreak was caused by a recently defined clade B lineage prevalent in Europe and was closely related, but not directly linked, to three European isolates. Additionally, over half (54.8%) of predicted multidrug resistance (MDR) isolates belonged to 10 MDR-associated MGT-STs, which were also frequent in Asian S. Enteritidis . Overall, this study investigated the genomic epidemiology of S. Enteritidis in Australia, including the first large local outbreak, using MGT. The open MGT platform enables a standardized and sharable nomenclature that can be effectively applied to public health for unified surveillance of S. Enteritidis nationally and globally. IMPORTANCE Salmonella enterica serovar Enteritidis is a leading cause of foodborne infections. We previously developed a genomic typing database (MGTdb) for S. Enteritidis to facilitate global surveillance of this pathogen. In this study, we examined the genomic features of Australian S. Enteritidis using the MGTdb and found that Australian S. Enteritidis is mainly epidemiologically linked with Asian strains (especially strains carrying antimicrobial resistance genes), followed by European strains. The first large-scale egg-associated local outbreak in Australia was caused by a recently defined lineage prevalent in Europe, and three European isolates in the MGTdb were closely related but not directly linked to this outbreak. In summary, the S. Enteritidis MGTdb open platform is shown to be a potentially powerful tool for national and global public health surveillance of this pathogen.

Assessing evidence of a potential Salmonella transmission across the poultry food chain

Enhanced Salmonella surveillance programmes in poultry were implemented in all European Member States, with minimum prevalence targets for a list of targeted serotypes to safeguard food and public health. Based on the Belgian Salmonella surveillance programme and focusing on poultry, the overarching aim of this study was to highlight possible Salmonella transmissions across the food chain (FC). For this purpose, firstly, the prevalence patterns of Salmonella (targeted and the most prevalent non-targeted) serotypes along the FC were described over time. Secondly, the effectiveness of the control measures against vertical transmission (breeders to 1-day-old broiler and layer chicks) was indirectly assessed by looking into the odds of targeted serotypes detection. Thirdly, it was appraised if Salmonella prevalence can significantly increase during broilers and layers production. In addition, it was tested if being tested negative at the end of production in broilers when tested positive at the entrance is serotype dependent (targeted vs. non-targeted serotypes). Results showed that, firstly, the prevalence patterns of the listed serotypes were inconstant over time and across the FC. Secondly, the odds of Salmonella targeted serotype detection in 1-day-old broiler and in 1-day-old layer flocks were lower than in breeder flocks while, thirdly, infection during broiler and layer production can lead to significant increase in positivity in subsequent samples. Finally, being infected by a targeted or by non-targeted serotype at the entrance of the flock poorly reflects the Salmonella status at the end of production. Note that this study did not make a distinction between the different sources of contamination and the effects of sampling methods and isolation methods should be subject to further investigation.

Effects of cinnamon essential oil on the physiological metabolism of Salmonella enteritidis

Food safety and health are the themes of today's society. As a class of foodborne pathogens, Salmonella enteritidis has become one of the common zoonotic pathogens. Because chemical preservatives have certain harmfulness and have been questioned, it is particularly important to find green and safe natural preservatives. The advantages of plant essential oils (EOs) are that they are green and safe, have a wide range of antibacterials, and are not easy to form drug resistance. In recent years, studies have found that EOs have excellent antibacterial activity, but their antibacterial mechanism has not been conclusive, which has certain limitations in their application in the food field. Cinnamon essential oil (CEO) extracted from dried cinnamon is a secondary metabolite of cells and a very important natural food flavor. More importantly, it is non-toxic to the human body and has been proven to have a good antibacterial effect, but its antibacterial mechanism is still unclear. Therefore, it was of great practical significance to carry out the research on the antibacterial mechanism of CEO on S. enteritidis. In this work, S. enteritidis was used as the test bacteria, and CEO was selected as the antibacterial agent to study the antibacterial mechanisms. By studying the physiological metabolism of S. enteritidis cells by CEO, the influence of CEO on the bacteriostatic mechanism of S. enteritidis was systematically elucidated. The study found that CEO treatment would reduce the activity of bacterial metabolism. It is mainly reflected in the following three aspects: first, the activity of key enzymes in TCA circulation is inhibited, thus affecting the respiration of S. enteritidis. Second, it affects the level of energy metabolism by inhibiting the content of adenosine triphosphate (ATP) and the activity of ATPase. Finally, it can affect the physiological metabolism of bacteria by inhibiting the metabolism of proteins and other substances. Therefore, this article was expected to provide a theoretical basis for the development of new natural food preservatives and the prevention and control of S. enteritidis.

Phenotypic and genotypic characterization of antimicrobial resistance profiles in Salmonella isolated from waterfowl in 2002–2005 and 2018–2020 in Sichuan, China

Salmonella enterica is a widespread foodborne pathogen with concerning antimicrobial resistance (AMR). Waterfowl are a major source of Salmonella transmission, but there are few systematic studies on Salmonella prevalence in waterfowl species. In this study, 126 Salmonella isolates (65 collected in 2018–2020 and 61 collected in 2002–2005) were obtained from waterfowl samples in Sichuan, China. Their serotypes, pulsed-field gel electrophoresis (PFGE) types, and phenotypic and genotypic AMR profiles were systematically examined. The isolates were distributed in 7 serotypes, including serovars Enteritidis (46.0%), Potsdam (27.8%), Montevideo (7.9%), Cerro (6.3%), Typhimurium (4.8%), Kottbus (4.0%) and Apeyeme (3.2%). Their PFGE characteristics were diverse; all isolates were distributed in four groups (cutoff value: 60.0%) and 20 clusters (cutoff value: 80.0%). Moreover, all isolates were multidrug resistant, and high rates of AMR to lincomycin (100.0%), rifampicin (100.0%), sulfadiazine (93.7%), erythromycin (89.7%), ciprofloxacin (81.0%), and gentamicin (75.4%) were observed. Finally, 49 isolates were subjected to whole-genome sequencing, and a wide variety of AMR genes were found, including multiple efflux pump genes and specific resistance genes. Interestingly, the tet(A)/tet(B) and catII resistance genes were detected in only isolates obtained in the first collection period, while the gyrA (S83F, D87N and D87G) and gyrB (E466D) mutations were detected at higher frequencies in the isolates obtained in the second collection period, supporting the findings that isolates from different periods exhibited different patterns of resistance to tetracycline, chloramphenicol and nalidixic acid. In addition, various incompatible plasmid replicon fragments were detected, including Col440I, Col440II, IncFIB, IncFII, IncX1, IncX9, IncI1-I and IncI2, which may contribute to the horizontal transmission of AMR genes and provide competitive advantages. In summary, we demonstrated that the Salmonella isolates prevalent in Sichuan waterfowl farms exhibited diverse serotypes, multiple AMR phenotypes and genotypes, and AMR changes over time, indicating their potential risks to public health.

Research Note: Internal Organ Colonization by Salmonella Enteritidis in Experimentally Infected Layer Pullets Reared at Different Stocking Densities in Indoor Cage-Free Housing

Contamination of eggs by Salmonella has often been identified as a source of food-borne human illness. S. Enteritidis is deposited inside developing eggs when invasive infections of laying hens reach the reproductive organs. The susceptibility of hens in cage-based housing systems to S. Enteritidis has been associated with their stocking density, but the applicability of this information to extensive (cage-free) systems is uncertain. The present study assessed internal organ colonization by S. Enteritidis in egg-type pullets reared at 2 different stocking densities in cage-free housing. Pullets were reared at either 374 cm² or 929 cm² of floor space per bird. At 16 wk of age, 4 groups of 72 pullets were moved into isolation rooms simulating commercial cage-free barns; 1/3 of the pullets in 2 rooms were orally inoculated with S. Enteritidis immediately after transfer and pullets in 2 rooms were similarly infected at 19 wk. At 6 and 12 d postinoculation, the pullets were euthanized and samples of liver, spleen, and intestinal tract were removed for bacteriologic culturing. No significant differences (P > 0.05) in S. Enteritidis isolation frequencies from any tissue were observed between high and low density rearing groups following infection at either age. However, S. Enteritidis was found significantly (P < 0.05) more frequently among pullets infected orally at 19 wk than at 16 wk in spleens and intestines. Likewise, the frequency of S. Enteritidis isolation from all birds (inoculated plus contact-exposed) at 19 wk was significantly higher than at 16 wk in livers and spleens. This increased susceptibility to invasive S. Enteritidis infection at reproductive maturity emphasizes the importance of risk reduction at a critical stage in the egg production cycle.

Efficacy of pectin-based caproic acid, caprylic acid, linalool, and cuminaldehyde coatings in reducing Salmonella Heidelberg on chicken eggs

Among the animal derived food products, contamination of poultry eggs, and egg shell surface is one of the major causes for foodborne salmonellosis in the United States. As a means of reducing the pathogen transfer to the internal egg contents, polysaccharide-based coatings containing antimicrobial phytochemicals could potentially serve as a biocontrol strategy for shelled egg products. The current study investigated the efficacy of four GRAS (Generally Recognized as Safe)-status plant-derived compounds, namely, caproic acid (CAO), caprylic acid (CAY), linalool (LIN) and cuminaldehyde (CUM), as pectin-based coating treatments, individually or in combination, for reducing Salmonella Heidelberg (SH) on shell eggs. A three-strain mixture of SH (~8.0 log CFU in 50 μL inoculum) was spot-inoculated on surface sterilized white-shelled eggs. Eggs were evenly coated with either pectin-based treatments of CAO (1%), CAY (1%), LIN (1%) and CUM (1%), individually, or a combination of 4 phytochemicals (COMB- each phytochemical at 0.5% v/v level of inclusion). The treated eggs were stored at 4°C and SH counts were enumerated on days 0, 1, 3, 5, 7, 14, and 21 of storage. The study was replicated thrice, 3 eggs/treatment/day time point, and the data were analyzed using two-way ANOVA with significance tested at p &lt; 0.05. On day 0, pectin-coated control eggs had ~7.6 log CFU of SH/egg. At the end of refrigerated storage (day 21), pectin-based coating of CAO and CAY at 1% level reduced SH by 2.0–2.5 log CFU/egg (P &lt; 0.05) when compared to controls. In addition, the CUM and LIN based coatings produced 3.0 log and 3.9 log reduction, respectively, in SH counts on eggs by day 21 of storage. Among the treatments with phytochemical combinations, COMB1 [pectin (2%) + Caprylic acid, caproic acid and cuminaldehyde (each at 0.5% level)] was found to be most effective, reducing SH counts to 2.5–3.3 log CFU/egg from day 0 through day 14, and by the end of storage period (day 21), a 3.5 log CFU reduction/egg (p &lt; 0.05) compared to untreated controls. Morphological studies of treated eggs using atomic force microscopy (AFM) have shown that the roughness of eggs can be influenced by a combination of various compounds. Results indicate the potential efficacy of the aforesaid phytochemicals in reducing SH on shell eggs; however, further studies investigating their industrial feasibility and effects on sensory attributes of eggs are warranted.

Effects of Cinnamon Essential Oil on Oxidative Damage and Outer Membrane Protein Genes of Salmonella enteritidis Cells

Salmonella is an important pathogen causing food poisoning. Food safety and health are the themes of today′s society. As a class of food-borne pathogens, Salmonella enteritidis had become one of the common zoonotic pathogens. Cinnamon essential oil (CEO) had been reported as an antibacterial agent, but there are few studies on its antibacterial mechanism. This study investigated the effects of CEO on oxidative damage and outer membrane protein genes of Salmonella enteritidis cells. First, the reactive oxygen species content in bacteria treated with different concentrations of cinnamon essential oil was determined by fluorescence spectrophotometry, and the effects of superoxide dismutase (SOD), catalase (CAT) and superoxide dismutase (SOD), and catalase (CAT) and peroxidase (POD) were determined by the kit method. The activity of POD and the content of malondialdehyde (MDA) were investigated to investigate the oxidative damage of CEO to Salmonella enteritidis cells. By analyzing the effect of CEO on the Salmonella enteritidis cell membrane’s outer membrane protein gene expression, the mechanism of CEO′s action on the Salmonella enteritidis cell membrane was preliminarily discussed. The results showed that CEO treatment had an obvious oxidative damaging effect on Salmonella enteritidis. Compared with the control group, the increase in CEO concentration caused a significant increase in the bacteria ROS content. The observation technique experiment found that with the increase in CEO concentration, the number of stained cells increased, which indicated that CEO treatment would increase the ROS level in the cells, and it would also increase with the increase in CEO concentration, thus causing the oxidation of cells and damage. In addition, CEO treatment also caused the disruption of the balance of the cellular antioxidant enzymes (SOD, CAT, POD) system, resulting in an increase in the content of MDA, a membrane lipid metabolite, and increased protein carbonylation, which ultimately inhibited the growth of Salmonella enteritidis. The measurement results of cell membrane protein gene expression levels showed that the Omp genes to be detected in Salmonella enteritidis were all positive, which indicated that Salmonella enteritidis carried these four genes. Compared with the control group, the relative expressions of OmpF, OmpA and OmpX in the CEO treatment group were significantly increased (p < 0.05), which proved that the cell function was disturbed. Therefore, the toxicity of CEO to Salmonella enteritidis could be attributed to the damage of the cell membrane and the induction of oxidative stress at the same time. It was speculated that the antibacterial mechanism of CEO was the result of multiple effects. This work was expected to provide a theoretical basis for the development of new natural food preservatives and the prevention and control of Salmonella enteritidis.

SARS-CoV-2 and Emerging Foodborne Pathogens: Intriguing Commonalities and Obvious Differences

The coronavirus disease 2019 (COVID-19) has resulted in tremendous human and economic losses around the globe. The pandemic is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a virus that is closely related to SARS-CoV and other human and animal coronaviruses. Although foodborne diseases are rarely of pandemic proportions, some of the causative agents emerge in a manner remarkably similar to what was observed recently with SARS-CoV-2. For example, Shiga toxin-producing Escherichia coli (STEC), the most common cause of hemolytic uremic syndrome, shares evolution, pathogenesis, and immune evasion similarities with SARS-CoV-2. Both agents evolved over time in animal hosts, and during infection, they bind to specific receptors on the host cell's membrane and develop host adaptation mechanisms. Mechanisms such as point mutations and gene loss/genetic acquisition are the main driving forces for the evolution of SARS-CoV-2 and STEC. Both pathogens affect multiple body organs, and the resulting diseases are not completely cured with non-vaccine therapeutics. However, SARS-CoV-2 and STEC obviously differ in the nature of the infectious agent (i.e., virus vs. bacterium), disease epidemiological details (e.g., transmission vehicle and symptoms onset time), and disease severity. SARS-CoV-2 triggered a global pandemic while STEC led to limited, but sometimes serious, disease outbreaks. The current review compares several key aspects of these two pathogenic agents, including the underlying mechanisms of emergence, the driving forces for evolution, pathogenic mechanisms, and the host immune responses. We ask what can be learned from the emergence of both infectious agents in order to alleviate future outbreaks or pandemics.

Antagonistic activity and mechanism of Lactobacillus rhamnosus SQ511 against Salmonella enteritidis

Salmonella enteritidis is an important food-borne pathogen. The use of antibiotics is a serious threat to animal and human health, owing to the existence of resistant strains and drug residues. Lactic acid bacteria, as a new alternative to antibiotics, has attracted much attention. In this study, we investigated the antibacterial potential and underlying mechanism of Lactobacillus rhamnosus SQ511 against S. enteritidis ATCC13076. The results revealed that L. rhamnosus SQ511 significantly inhibited S. enteritidis ATCC13076 growth or even caused death. Laser confocal microscopic imaging revealed that the cell-free supernatant (CFS) of L. rhamnosus SQ511 elevated the reactive oxygen species level and bacterial membrane depolarization in S. enteritidis ATCC13076, leading to cell death. Furthermore, L. rhamnosus SQ511 CFS had severely deleterious effects on S. enteritidis ATCC13076, causing membrane destruction and the release of cellular materials. In addition, L. rhamnosus SQ511 CFS significantly reduced the expression of virulence, motility, adhesion, and invasion genes in S. enteritidis ATCC13076 (P < 0.05), and considerably inhibited motility and biofilm formation capacity (P < 0.05). Thus, antimicrobial compounds produced by L. rhamnosus SQ511 strongly inhibited S. enteritidis growth, mobility, biofilm formation, membrane disruption, and reactive oxygen species generation, and regulated virulence-related gene expressions, presenting promising applications as a probiotic agent.

A Severe Gastroenteritis Outbreak of Salmonella enterica Serovar Enteritidis Linked to Contaminated Egg Fried Rice, China, 2021

Salmonella contamination of eggs and egg shells has been identified as a public health problem worldwide. Here, we reported an outbreak of severe gastrointestinal symptoms caused by Salmonella enterica serovar Enteritidis (S. enteritidis) in China. We evaluated the outbreak by using epidemiological surveys, routine laboratory testing methods, and whole genome sequencing (WGS). This outbreak occurred in a canteen in Beijing, during March 9–11, 2021, 225 of the 324 diners who have eaten at the canteen showed gastrointestinal symptoms. The outbreak had characteristical epidemiological and clinical features. It caused a very high attack rate (69.4%) in a short incubation time. All patients developed diarrhea and high fever, accompanied by abdominal pain (62.3%), nausea (50.4%), and vomiting (62.7%). The average frequency of diarrhea was 12.4 times/day, and the highest frequency of diarrhea was as high as 50 times/day. The average fever temperature was 39.4°C, and the highest fever temperature was 42°C. Twenty strains of S. enteritidis were recovered, including 19 from the patients samples, and one from remained egg fried rice. Antibiotic susceptibility test showed that the 20 outbreak strains all had the same resistance pattern. PFGE results demonstrated that all 20 strains bore completely identical bands. Phylogenetic analysis based on WGS revealed that all 20 outbreak strains were tightly clustered together. So the pathogenic source of this food poisoning incident may was contaminated egg fried rice. Resistance gene analysis showed that the outbreak strains are all multi-drug resistant strains. Virulence gene analysis indicated that these outbreak strains carried a large number of virulence genes, including 2 types of Salmonella pathogenicity islands (SPI-1 and SPI-2). Other important virulence genes were also carried by the outbreak strains, such as pefABCD, rck and shdA. And the shdA gene was not in other strains located in the same evolutionary branch as the outbreak strain. We speculated that this is a significant reason for the serious symptoms of gastroenteritis in this outbreak. This outbreak caused by S. enteritidis suggested government should strengthen monitoring of the prevalence of outbreak clone strains, and take measures to mitigate the public health threat posed by contaminated eggs.

Research Note: Contamination of eggs by Salmonella Enteritidis and Salmonella Typhimurium in experimentally infected laying hens in indoor cage-free housing

Contaminated eggs are a leading source of human Salmonella infections and this problem continues to challenge public health authorities and egg industries around the world. Salmonella invasion of the ovaries and oviducts of infected laying hens can result in bacterial deposition inside the edible portions of developing eggs. The introduction, persistence, and transmission of salmonellae in commercial egg-laying flocks are influenced by flock management practices, but the food safety ramifications of different types of laying hen housing remain unresolved. The present study assessed the frequency of internal contamination of eggs after experimental Salmonella Enteritidis and S. Typhimurium infection of laying hens in indoor cage-free housing. Groups of 72 hens were housed on wood shavings in isolation rooms simulating commercial cage-free barns with community kick-out nest boxes and perches and 1/3 of the hens in each room were orally inoculated with 8.0 × 10⁷ cfu of 2-strain mixtures of either S. Enteritidis (2 rooms) or S. Typhimurium (2 rooms), and the entire internal contents of all eggs laid 5 to 30 d postinoculation in nest boxes or on the flooring substrate were cultured to detect Salmonella. Contaminated eggs were laid between 8 and 28 d postinoculation. The overall incidence of S. Enteritidis isolation from eggs (3.41%) was significantly (P = 0.0005) greater than S. Typhimurium (1.19%). The contamination frequencies associated with the 2 egg collection locations were not significantly different (P > 0.05). These results demonstrate that oral infection of a relatively small proportion of laying hens in indoor cage-free housing with invasive Salmonella serovars can result in the production of internally contaminated eggs at low frequencies over a period of nearly a month postinoculation.

Heavy Metal Resistance in Salmonella Typhimurium and Its Association With Disinfectant and Antibiotic Resistance

Metals are widely used in animal feed for their growth-stimulating and antimicrobial effects, yet their use may potentially promote the proliferation of antibiotic resistance through co-selection. We studied the prevalence and associations of metal, antibiotic, and disinfectant resistances of 300 Salmonella Typhimurium isolates from pig meat, pig manure, chicken meat, poultry manure, and human stool from Sichuan, China. Seventy four percent of the 300 Salmonella Typhimurium isolates were considered resistant to Cu, almost 50% to Zn and Cr, over 25% to Mn and Cd, and almost 10% to Co. Most of the isolates carried at least one heavy metal resistance gene (HMRG). The Cr-Zn-Cd-resistance gene czcD was carried by 254 isolates and the Cu-resistance genes pcoR and pcoC by 196 and 179 isolates, respectively. Most of the isolates were resistant to at least one antibiotic and almost 80% were multidrug-resistant. The prevalence of resistance to six antibiotics was higher among the pig meat and manure isolates than among other isolates, and that of streptomycin and ampicillin were highest among the pig meat isolates and that of ciprofloxacin and ofloxacin among the pig manure isolates. From 55 to 79% of the isolates were considered resistant to disinfectants triclosan, trichloroisocyanuric acid, or benzalkonium chloride. The metal resistances and HMRGs were associated with resistance to antibiotics and disinfectants. Especially, Cu-resistance genes were associated with resistance to several antibiotics and disinfectants. The transfer of the Cr-Zn-Cd-resistance gene czcD, Cu-resistance gene pcoC, and Co-Ni-resistance gene cnrA into Escherichia coli and the increased Cu-resistance of the transconjugants implied that the resistance genes were located on conjugative plasmids. Thus, the excessive use of metals and disinfectants as feed additives and in animal care may have the potential to promote antibiotic resistance through co-selection and maintain and promote antibiotic resistance even in the absence of antibiotics.

Effect of dietary direct-fed microbial and yeast cell walls on cecal digesta microbiota of layer chicks inoculated with nalidixic acid resistant Salmonella Enteritidis

Salmonella enterica serovar Enteritidis (SE) has consistently been the most common serotype associated with the foodborne Salmonellosis worldwide. In this study, the effect of a dietary direct-fed microbial (DFM) and yeast cell walls (YCW) under a challenge of nalidixic acid resistant SE strain using layer chicks has been investigated. A total of 160 newly hatched Dekalb White female chicks were randomly assigned into 2 experimental groups (80 birds/treatment), control group (CON) and treatment group (DY). Chicks were fed ad libitum a non–medicated-corn-soy based diet and DY was supplemented with the combination of DFM and YCW. At 8 days of age, 2.1 × 10⁹ CFU/bird of the SE was given to all chicks by oral administration. On 3 days postinoculation (dpi), 20 chicks/group were euthanized and all cecal contents were collected for analysis. On 6, 10, and 14 dpi, the cecal contents were sampled from 16 chicks per group. The number of SE in the cecal contents was counted using culture-based methods. A 16S rRNA-based microbiota analysis was performed for additional microbial profiling. The CON and DY showed difference (P ≤ 0.05) in β diversity throughout the trial. Prevalence of SE in cecal contents was lower (P ≤ 0.05) in DY across all time-points. Lower abundance of Salmonella spp. was also shown in DY by liner discriminant analysis effect size (LEfSe). DY increased (P ≤ 0.05) diversity of bacterial species in the cecal contents in DY at 10 and 14 dpi. For the SE challenged birds, SE reduction in DY was observed at 3 dpi and until the end of the trial at 14 dpi confirming a numerically larger difference between groups as well as an increase in bacterial species diversity in DY. It could be hypothesized that the SE reduction shown immediately after the challenge and the greater SE reduction shown after 10 dpi may be the synergistic effect of the combined feed additives.

Prebiotics and alternative poultry production

Alternative poultry production systems continue to expand as markets for organic and naturally produced poultry meat and egg products increase. However, these production systems represent challenges associated with variable environmental conditions and exposure to foodborne pathogens. Consequently, there is a need to introduce feed additives that can support bird health and performance. There are several candidate feed additives with potential applications in alternative poultry production systems. Prebiotic compounds selectively stimulate the growth of beneficial gastrointestinal microorganisms leading to improved health of the host and limiting the establishment of foodborne pathogens. The shift in the gastrointestinal microbiota and modulation of fermentation can inhibit the establishment of foodborne pathogens such as Campylobacter and Salmonella. Both current and potential applications of prebiotics in alternative poultry production systems will be discussed in this review. Different sources and types of prebiotics that could be developed for alternative poultry production will also be explored.

Identification of Differentially Expressed Non-coding RNA Networks With Potential Immunoregulatory Roles During Salmonella Enteritidis Infection in Ducks

Salmonella enterica serovar Enteritidis (S. Enteritidis) is a pathogen that can colonize the preovulatory follicles of poultry, thereby causing both reduced egg production and an elevated risk of foodborne salmonellosis in humans. Although a few studies have revealed S. Enteritidis preferentially invades the granulosa cell layer within these follicles, it can readily persist and proliferate through mechanisms that are not well-understood. In this study, we characterized competing endogenous RNA (ceRNA) regulatory networks within duck granulosa cells following time-course of S. Enteritidis challenge. The 8108 long non-coding RNAs (lncRNAs), 1545 circular RNAs (circRNAs), 542 microRNAs (miRNAs), and 4137 mRNAs (fold change ≥2; P < 0.01) were differentially expressed during S. Enteritidis challenge. Also, eight mRNAs, eight lncRNAs and five circRNAs were selected and the consistent expression trend was found between qRT-PCR detection and RNA-seq. Moreover, the target genes of these differentially expressed ncRNAs (including lncRNAs, circRNAs and miRNAs) were predicted, and significantly enriched in the innate immune response and steroidogenesis pathways. Then, the colocalization and coexpression analyses were conducted to investigate relationships between ncRNAs and mRNAs. The 16 differentially expressed miRNAs targeting 60 differentially expressed mRNAs were identified in granulosa cells at 3 and 6 h post-infection (hpi) and enriched in the MAPK, GnRH, cytokine-cytokine receptor interaction, Toll-like receptor, endocytosis, and oxidative phosphorylation signaling pathways. Additionally, underlying lncRNA-miRNA-mRNA and circRNA-miRNA-mRNA ceRNA networks were then constructed to further understand their interaction during S. Enteritidis infection. Lnc_012227 and novel_circ_0004892 were identified as ceRNAs, which could compete with miR-let-7g-5p and thereby indirectly modulating map3k8 expression to control S. Enteritidis infection. Together, our data thus identified promising candidate ncRNAs responsible for regulating S. Enteritidis infection in the preovulatory follicles of ducks, offering new insights regarding the ovarian transmission of this pathogen.

Occurrence of Escherichia coli and Salmonella species in Some Livestock (Poultry) Feeds in Mando, Kaduna, Nigeria

The study aimed at assessing the proximate composition, isolation, characterization of some Enterobacteriaceae from two (2) brands of poultry feeds marketed in Mando, Kaduna, Nigeria. A total of sixteen (16) samples of two (2) different poultry feeds (starter and finisher) from four (4) poultry farms in mando were collected and subjected to proximate and microbiological analysis. The proximate analysis was carried out using standard techniques and procedures. All the feed samples were cultured on separate media which include Eosin methylene blue (EMB), nutrient Agar (NA) and Salmonella-Shigella Agar (SSA) media using standard procedures. The antibiogram of the selected antibiotics was evaluated against the test isolates. The result of proximate analysis of the starter and finisher feeds indicated that the Dry matter of starter feed had the highest percentage composition of 95.02% and crude fiber of the finisher feed had the lowest composition of 3.78%. The highest number of bacterial load was recorded to be 10.0×104 CFU/g for the feed sample A (starter feed) and 12.0x104CFU/g was recorded for the feed sample B (finisher feed) which had the highest number of bacterial load recorded among the two (2) different poultry feeds analyzed. The bacteria isolates were identified as Salmonella species and Escherichia coli. Total viable count (TVC) of Salmonella species and E. coli in the feed samples (starter and finisher) ranges from 3.0×104CFU/g to 12.0×104CFU/g. Both organisms (Salmonella species, E. coli) were found as 37.5% and 25% of the analyzed feeds (Broiler starter and broiler finisher) samples, respectively. There was no level of significant (p>0.05) difference between the level of contamination of Salmonella species and E. coli in the two different feeds analyzed, as p=0.06 and p=0.13 for Salmonella species, and E. coli respectively. Sample A and B (Starter and Finisher) feeds had the highest number of Salmonella species occurrence with six ( 6) positive samples while E. coli was recorded in four (4) samples of A and B (Starter and Finisher) feeds. The result of the antibiogram indicated that ciprofloxacin (30 µg), Gentamycin (30µg), Perfloxacin (30µg) and Tarvid (30µg) was effective against Salmonella species and Escherichia coli. The significant of spread of the species of the Enterobacteriaceae in livestock feeds requires the need for effective quality assurance and control, good hygiene practices in production and proper handling of the poultry feeds.

Biofilm-Formation-Related Genes csgD and bcsA Promote the Vertical Transmission of Salmonella Enteritidis in Chicken

The contamination of Salmonella Enteritidis in eggs and chicken meat via vertical transmission has become a worldwide public health concern. Biofilm formation by S. Enteritidis further enhances its antibacterial resistance. However, whether genes related to biofilm formation affect the level of vertical transmission is still unclear. Here, S. Enteritidis mutants ΔcsgD, ΔcsgA, ΔbcsA, and ΔadrA were constructed from wild type strain C50041 (WT), and their biofilm-forming ability was determined by Crystal violet staining assay. Then the median lethal dose (LD₅₀) assay was performed to determine the effects of the selected genes on virulence. The bacterial load in eggs produced by infected laying hens via the intraperitoneal pathway or crop gavage was determined for evaluation of the vertical transmission. Crystal violet staining assay revealed that S. Enteritidis mutants ΔcsgD, ΔcsgA, and ΔbcsA, but not ΔadrA, impaired biofilm formation compared with WT strain. Furthermore, the LD₅₀ in SPF chickens showed that both the ΔcsgD and ΔbcsA mutants were less virulent compared with WT strain. Among the intraperitoneally infected laying hens, the WT strain-infected group had the highest percentage of bacteria-positive eggs (24.7%), followed by the ΔadrA group (16%), ΔcsgA group (9.9%), ΔbcsA group (4.5%), and ΔcsgD group (2.1%). Similarly, among the crop gavage chickens, the WT strain group also had the highest infection percentage in eggs (10.4%), followed by the ΔcsgA group (8.5%), ΔadrA group (7.5%), ΔbcsA group (1.9%), and ΔcsgD group (1.0%). Our results indicate that the genes csgD and bcsA help vertical transmission of S. Enteritidis in chickens.

Absence of high priority critically important antimicrobial resistance in Salmonella sp. isolated from Australian commercial egg layer environments

The development of antimicrobial resistance in foodborne pathogens is a growing public health concern. This study was undertaken to determine the antimicrobial susceptibility of Salmonella enterica subspecies enterica isolated from the Australian commercial egg layer industry. S. enterica subspecies enterica (n=307) isolated from Australian commercial layer flock environments (2015-2018) were obtained from reference, research and State Government laboratories from six Australian states. All Salmonella isolates were serotyped. Antimicrobial susceptibility testing (AST) for 16 antimicrobial agents was performed by broth microdilution. Antimicrobial resistance genes and sequence types (STs) were identified in significant isolates by whole genome sequencing (WGS). Three main serotypes were detected, S. Typhimurium (n=61, 19.9%), S. Senftenburg (n=45, 14.7%) and S. Agona (n=37, 12.1%). AST showed 293/307 (95.4%) isolates were susceptible to all tested antimicrobial agents and all isolates were susceptible to amoxicillin-clavulanate, azithromycin, ceftiofur, ceftriaxone, ciprofloxacin, colistin, florfenicol, gentamicin, kanamycin and trimethoprim-sulfamethoxazole. Low levels of non-susceptibility were observed to streptomycin (2.3%, n=7), sulfisoxazole (2.0%, n=6), chloramphenicol (1.3%, n=4) and tetracycline (1.0%, n=3). Very low levels of non-susceptibility were observed to ampicillin (2/307; 0.7%) and cefoxitin (2/307; 0.7%). Two isolates (S. Havana and S. Montevideo), exhibited multidrug-resistant phenotypes to streptomycin, sulfisoxazole and tetracycline and possessed corresponding antimicrobial resistance genes (aadA4, aac(6')-Iaa, sul1, tetB). One S. Typhimurium isolate was resistant to ampicillin and tetracycline, and possessed both tetA and bla_TEM-1B. WGS also identified these isolates as belonging to ST4 (S. Montevideo), ST578 (S. Havana) and ST19 (S. Typhimurium). The absence of resistance to highest priority critically important antimicrobials as well as the extremely low level of AMR generally among Australian commercial egg layer Salmonella isolates likely reflect Australia's conservative antimicrobial registration policy in food-producing animals and low rates of antimicrobial use within the industry.

Challenges in Vaccinating Layer Hens against Salmonella Typhimurium

Salmonella Typhimurium is among the most common causes of bacterial foodborne gastrointestinal disease in humans. Food items containing raw or undercooked eggs are frequently identified during traceback investigation as the source of the bacteria. Layer hens can become persistently infected with Salmonella Typhimurium and intermittently shed the bacteria over the course of their productive lifetime. Eggs laid in a contaminated environment are at risk of potential exposure to bacteria. Thus, mitigating the bacterial load on farms aids in the protection of the food supply chain. Layer hen producers use a multifaceted approach for reducing Salmonella on farms, including the all-in-all-out management strategy, strict biosecurity, sanitization, and vaccination. The use of live attenuated Salmonella vaccines is favored because they elicit a broader host immune response than killed or inactivated vaccines that have been demonstrated to provide cross-protection against multiple serovars. Depending on the vaccine, two to three doses of Salmonella Typhimurium vaccines are generally administered to layer hens within the first few weeks. The productive life of a layer hen, however, can exceed 70 weeks and it is unclear whether current vaccination regimens are effective for that extended period. The objective of this review is to highlight layer hen specific challenges that may affect vaccine efficacy.

Survey of Salmonella infections in broiler farms in Iran during 2013-2014: a cross-sectional study

Background and Objectives:

The aim of this study was to determine the prevalence of Salmonella at broiler breeder farms of Iran and investigate the factors underlying salmonellosis in these farms. This is a cross-sectional investigation conducted in 23 provinces of Iran.

Materials and Methods:

Fecal samples were collected from 139 broiler breeder farms in the country and standard bacteriological tests were carried out on the samples for the isolation of Salmonella. The serological tests were then applied for the samples that were positive in the bacteriological test. The information on the sampled farms extracted from the Iran GIS-VET Monitoring and Surveillance System was used for the analysis of the risk factors.

Results:

A total of 11 farms out of the 139 sampled farms were infected with Salmonella with the largest number of infected cases related to Tehran and Fars Provinces.

Conclusion:

The statistical analysis results showed that flocks with older ages and farms with larger number of houses are at greater risk of Salmonella infection.

Development of Salmonella Enteritidis vaccine candidate based on streptomycin independent suppressor and metabolic drift rifampicin resistance-attenuating markers

Salmonella is one of the most frequent food-borne pathogens and remains public health threat globally. The control of Salmonella in poultry, the main reservoir of non-typhoidal salmonellae, is a fundamental approach to ensure the safety of poultry products for human consumption. In the present study, a new live attenuated Salmonella enterica serovar Enteritidis vaccine candidate containing three attenuating markers based on streptomycin-independent (Sm-id) suppressor, and metabolic drift antibiotic resistance (MD- “res”) was developed. The streptomycin dependent (Smd) mutants were derived from Salmonella Enteritidis wild-type strain using streptomycin. Then the Sm-id mutants were derived from the isolated Smd mutants and designated “Smd→Sm-id”. A third MD- “res” marker was generated from Smd→Sm-id using rifampicin (Rif) and designated “Smd→Sm-id→Rif”. The colony sizes of these mutants were stable after more than 50 serial passages on blood agar; reversion to virulence can be almost excluded. The safety and efficacy of Smd→Sm-id and Smd→Sm-id→Rif were evaluated in one-day-old commercial layer chicks. Both mutants proved to be safe in terms of clinical signs, mortalities, lesion scores of visceral organs and rapid clearance when administered orally at a dose of 10⁸ colony forming unit (CFU), whereas birds inoculated with 10⁸ CFU Salmonella Enteritidis wild-type strain showed diarrhea, mortalities (3/40) and necrosis in liver and spleen. Chickens vaccinated with the developed mutants showed no seroconversion; however, wild-type strain induced a significant seroconversion at 3-week-postvaccination (wpv). The developed mutants protected chickens against challenge with 10⁸ CFU of Salmonella Enteritidis wild-type strain at 3-wpv. Vaccinated birds showed neither clinical signs nor mortalities during two-week post-challenge. In addition, the challenge strain could not be detected in pooled liver and spleen samples (0/5) at 7^th day post-inoculation (dpi). However, non-vaccinated challenged birds showed diarrhea and the challenge strain was re-isolated from pooled liver and spleen samples (3/5) at 7^th dpi. In conclusion, the developed mutants are safe and fully protected immunized chickens following heterologous challenge. It is obvious that the genetic characterization of these mutants and evaluation of different vaccination regimes are still in demand.

Research Note: Horizontal transmission and internal organ colonization by Salmonella Enteritidis and Salmonella Kentucky in experimentally infected laying hens in indoor cage-free housing

The transmission of Salmonella to humans via contaminated eggs is an international public health concern. S. Enteritidis is deposited inside eggs after colonizing reproductive tissues of infected hens. Diverse housing facility characteristics and flock management practices influence Salmonella persistence and transmission in poultry, but the food safety consequences of different housing systems for laying hens remain unresolved. The present study compared the horizontal transmission of infection and invasion of internal organs during the first 2 wk after experimental S. Enteritidis and S. Kentucky infection of laying hens in indoor cage-free housing. Groups of 72 hens were housed in isolation rooms simulating commercial cage-free barns, and 1/3 of the hens in each room were orally inoculated with either S. Enteritidis (2 rooms) or S. Kentucky (2 rooms). At 6 d and 12 d postinoculation, 12 inoculated and 24 contact-exposed hens in each room were euthanized, and samples of liver, spleen, ovary, oviduct, and intestinal tract were removed for bacteriologic culturing. All orally inoculated hens were positive for intestinal colonization by S. Enteritidis at 6 d postinfection, and 70.8% of contact-exposed hens had become colonized by 12 d. S. Enteritidis was isolated from 100% of livers and 50.0% of ovaries from inoculated birds at 6 d and from 41.7% of livers and 10.4% of ovaries from contact-exposed birds at 12 d. The majority of both orally inoculated and contact-exposed hens were positive for intestinal colonization by S. Kentucky at 6 d, but S. Kentucky was found in other internal organs of both inoculated and contact-exposed hens significantly (P < 0.05) less often than S. Enteritidis at both sampling intervals. These results indicate that Salmonella infection can spread rapidly and extensively among hens in cage-free indoor housing, including a high frequency of internal organ involvement for invasive S. Enteritidis.

Characterization of Salmonella spp. isolated from chickens in Central China

Background

Salmonella is an important zoonotic pathogen, and chickens are one of its main hosts. Every year, Salmonella infections pose a serious threat to the poultry industry in developing countries, especially China. In this study, a total of 84 Salmonella isolates recovered from sick and healthy-looking chickens in central China were characterized by serotyping, MLST-based strain typing, presence of potential virulence factors, and antimicrobial resistance profiles.

Result

Data showed that the main serotypes of Salmonella isolates in central China were Salmonella enterica serovar Gallinarum biovar Pullorum, Salmonella enterica serovar Gallinarum biovar Gallinarum, Salmonella enterica serovar Enteritidis and Salmonella enterica serovar Typhimurium, and among them, S. Pullorum was the dominant type in both sick and healthy-looking chickens, accounting for 43.9 and 46.5%, respectively, while S. Enteritidis was only found in healthy-looking chickens. All isolates exhibited higher resistance rates to ampicillin (97.6%), tetracycline (58.3%) and colistin (51.2%), and among these isolates, 49.5% were resistant to more than three drugs in different combinations. S. Enteritidis was the most severe multidrug-resistant serotype, which showed higher resistance rates to colistin, meropenem and ciprofloxacin. Multilocus sequence typing (MLST) revealed that S. Gallinarum and S. Enteritidis isolates were clustered in clade 1, which belonged to two and one STs, respectively. All S. Typhimurium isolates were clustered in clade 3, and belonged to three STs. However, S. Pullorum were distributed in three clades, which belonged to 7 STs. Twenty-seven virulence-associated genes were detected, and expected cdtB, which was absent in all the isolates, the other 26 genes were conserved in the closely related Salmonella serogroup D (S. Enteritidis, S. Pullorum, and S. Gallinarum).

Conclusion

Salmonella serogroup D was the major subgroup, and S. Pullorum was the most common type in sick and healthy-looking chickens in central China. Drug resistance assays showed serious multiple antimicrobial resistances, and S. Enteritidis was the most severe drug-resistant serotype. MLST showed that there was correlation between serotypes and genotypes in most Salmonella isolates, except S. Pullorum, which showed complicated genetic diversity firstly. These results provide important epidemiological information for us to control Salmonella in chickens.

Occurrence and Characterization of Salmonella Isolated from Table Egg Layer Farming Environments in Western Australia and Insights into Biosecurity and Egg Handling Practices

The aim of this study was to investigate the occurrence and distribution of Salmonella in commercial layer farming environments of 26 flocks belonging to seven egg businesses (free-range and barn-laid) in Western Australia (WA). Between November 2017 and June 2018, a total of 265 environmental samples of dust, feed, water, pooled feces, and boot swabs were tested for detection of Salmonella according to standard culture-based methods. Isolates were assayed for serovar and subtyped by multilocus sequence typing (MLST). Salmonella spp. were recovered from 35% (93/265) of all tested samples. Dust (53.8%, 28/52) and pooled fecal (54.5%, 18/33) samples provided the highest Salmonella recovery rates. Nine different Salmonella serovars were characterized across the positive (n = 93) environmental samples, of which S. Typhimurium (60/93, 64.5%) and S. Infantis (21/93, 22.5%) were the most prevalent. MLST revealed that all S. Typhimurium isolates were of sequence type ST-19. Microbiological screening of Salmonella was not routinely practiced in any of the surveyed egg businesses. Some of the egg businesses exhibited variable levels of compliance with basic biosecurity measures as well as high-risk egg handling practices. Egg businesses in WA should be encouraged to adopt a voluntary program of environmental sampling and verification testing for Salmonella. Such voluntary programs will aid in supporting solutions for the management of this pathogen in the human food chain.

Contamination of eggs by Salmonella Enteritidis in experimentally infected laying hens of four commercial genetic lines in conventional cages and enriched colony housing

Human illness caused by the consumption of eggs contaminated with Salmonella Enteritidis is a continuing international public health concern. This pathogen is deposited inside the edible contents of eggs as a consequence of its ability to colonize reproductive tissues in infected hens. Conditions in the housing environment can influence the persistence and transmission of avian Salmonella infections, but the food safety ramifications of different poultry management systems are not entirely clear. The present study assessed the deposition of S. Enteritidis inside eggs laid by groups of experimentally infected laying hens of 4 commercial genetic lines (designated as white egg lines W1 and W2 and brown egg lines B1 and B2). Groups of hens from each line were housed at 555 cm2 of floor space per bird in both conventional cages and colony units enriched with access to perches and nesting areas. All hens were orally inoculated with 5.75 × 107 cfu of a 2-strain S. Enteritidis mixture, and the internal contents of eggs laid 5 to 24 D post-inoculation were cultured to detect the pathogen. No significant differences in egg contamination frequencies were found between the 2 housing systems for any of the hen lines. Contaminated eggs were laid between 7 and 21 D post-inoculation at an overall frequency of 2.47%, ranging from 0.25 to 4.38% for the 4 hen lines. The frequency of S. Enteritidis recovery from egg samples was significantly (P < 0.05) lower for line B2 than for any of the other lines, and the egg contamination frequency for line W1 was significantly greater than for line W2. The overall incidence of contamination among white eggs (3.38%) was significantly higher than among brown eggs (1.56%). These results demonstrate that S. Enteritidis deposition inside eggs can vary between genetic lines of infected laying hens, but housing these hens in 2 different systems did not affect the production of contaminated eggs.