A comparative study on the pathogenesis of egg contamination by different serotypes ofSalmonella

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.

Prevalence and genomic characterization of Salmonella isolates from commercial chicken eggs retailed in traditional markets in Ghana

Salmonella enterica are important foodborne bacterial pathogens globally associated with poultry. Exposure to Salmonella-contaminated eggs and egg-related products is a major risk for human salmonellosis. Presently, there is a huge data gap regarding the prevalence and circulating serovars of Salmonella in chicken eggs sold in Ghana. In this study, 2,304 eggs (pools of six per sample unit) collected from informal markets in Accra, Kumasi and Tamale, representing the three ecological belts across Ghana, were tested for Salmonella. Antimicrobial susceptibility testing and Whole Genome Sequencing (WGS) of the isolates were performed using standard microdilution protocols and the Illumina NextSeq platform, respectively. The total prevalence of Salmonella was 5.5% with a higher rate of contamination in eggshell (4.9%) over egg content (1.8%). The serovars identified were S. Ajiobo (n = 1), S. Chester (n = 6), S. Hader (n = 7), S. enteritidis (n = 2); and S. I 4:b:- (n = 8). WGS analysis revealed varied sequence types (STs) that were serovar specific. The S. I 4:b:- isolates had a novel ST (ST8938), suggesting a local origin. The two S. enteritidis isolates belonged to ST11 and were identified with an invasive lineage of a global epidemic clade. All isolates were susceptible to ampicillin, azithromycin, cefotaxime, ceftazidime, gentamicin, meropenem, and tigecycline. The phenotypic resistance profiles to seven antimicrobials: chloramphenicol (13%), ciprofloxacin (94%), and nalidixic acid (94%), colistin (13%), trimethoprim (50%) sulfamethoxazole (50%) and tetracycline (50%) corresponded with the presence of antimicrobial resistance (AMR) determinants including quinolones (gyrA (D87N), qnrB81), aminoglycosides (aadA1), (aph(3")-Ib aph(6)-Id), tetracyclines (tet(A)), phenicols (catA1), trimethoprim (dfrA14 and dfrA1). The S. enteritidis and S. Chester isolates were multidrug resistant (MDR). Several virulence factors were identified, notably cytolethal distending toxin (cdtB gene), rck, pef and spv that may promote host invasion and disease progression in humans. The findings from this study indicate the presence of multidrug resistant and virulent strains of Salmonella serovars in Ghanaian chicken eggs, with the potential to cause human infections. This is a critical baseline information that could be used for Salmonella risk assessment in the egg food chain to mitigate potential future outbreaks.

Evaluation of the different methods to detect Salmonella in poultry feces samples

Salmonella is one of the most common causes of foodborne outbreaks and infection worldwide. The gold-standard detection method of Salmonella is cultivation. There is a need to investigate rapid and accurate processes with time-consuming cultivation. The study evaluated different approaches to detect Salmonella in poultry feces samples. Poultry farm feces samples from 21 cities in Iran were collected from January 2016 to December 2019. Microbiological cultures, serological assays, and multiplex PCR (m-PCR) were used to detect and characterize Salmonella spp. isolates. Serological assays and m-PCR were used to determine the serogroups A, B, C1, C2, D1, E, H, and FliC. The m-PCR was used to detect seven Salmonella serovars, and a Chi-square test was performed to compare the discriminatory power of the methods. Of 2300 poultry feces samples, 173 (7.5%) and 166 (7.2%) samples were detected as Salmonella spp. by cultivation and m-PCR, respectively. The sensitivity of the molecular method was equal to cultivation at 0.96 (CI = 95%). Assessment of H antigenic subgroups showed the same for both m-PCR and serological tests. Therefore, the matching rate of the two methods for detecting all H antigenic subgroups was 100%. Thus, the relationship between the results obtained from both methods was significant in the contingency table test (P < 0.01). The PCR-based approach confirmed the detection of Salmonella in a shorter period (24-36 h) compared to the conventional microbiological approach (3-8 days).

The application of a novel non-thermal plasma device with double rotary plasma jets for inactivation of Salmonella Enteritidis on shell eggs and its effects on sensory properties

Consumer awareness and distaste towards both bacterial and chemical contaminations on food items have been increasing in recent years. Non-thermal plasma (NTP) is a cutting-edge technology which has been shown to effectively inactivate bacteria on the treated foods. Although the general NTP with a single plasma jet is appropriate for the continuous operation process, it suffers limitations due to its smaller scanning area. Here, a novel NTP device with a double rotary nozzle jet system was utilized, which could treat an area instead of a point. The shell eggs inoculated with Salmonella enterica serotype Enteritidis (SE) were placed on a moving platform under the double rotary nozzle jet system. The efficacy of the NTP treatment on microbial decontamination was evaluated by testing a total of 26 combinations of operating parameters consisting of various plasma power (150, 180, 210 W), argon flow rate (10, 15, 20 slm), repetition of the moving platform (4, 6, 8 times), and speed of the moving platform (5, 10 mm/s). Although significantly higher SE reduction (p < 0.05) was achieved with higher power, more repetitions, larger argon flow rates, and lower speed of the platform, these parameters induced significant alterations in the sensory properties of the treated eggs. By comprehensively considering the bacterial reductions, egg quality, and sensory properties, NTP treatment with combination T (180 W-15 slm-6 times-10 mm/s) was determined to be the optimal parameter, which achieved >4 log CFU/egg of SE reduction and significantly better sensory properties than commercially washed eggs (p < 0.05). Additionally, SEM analysis revealed that NTP treatment with combination T resulted in less damage to egg cuticles compared to commercially washed eggs. This novel NTP device offers an efficient antibacterial activity under shorter exposure time (30 s), smaller argon flow rate (15 slm), and lower power (180 W) without adversely affecting the overall quality of the treated eggs. Therefore, this NTP device equipped with the double rotary jet system possesses a potential solution for future industrial applications.

Identification of New Antimicrobial Peptides that Contribute to the Bactericidal Activity of Egg White against Salmonella enterica Serovar Enteritidis at 45 °C

A recent work revealed that egg white (EW) at 45 °C exhibits powerful bactericidal activity against S. enterica serovar Enteritidis, which is surprisingly little affected by removal of the >10 kDa EW proteins. Here, we sought to identify the major EW factors responsible for this bactericidal activity by fractionating EW using ultrafiltration and nanofiltration and by characterizing the physicochemical and antimicrobial properties of the resulting fractions. In particular, 22 peptides were identified by nano-LC/MS-MS and the bactericidal activities of representative peptides (with predicted antimicrobial activity) were further assessed. Two peptides (FVPPVQR and GDPSAWSWGAEAHS) were found to be bactericidal against S. enterica serovar Enteritidis at 45 °C when provided in an EW environment. Nevertheless, these peptides contribute only part of this bactericidal activity, suggesting other, yet to be determined, antimicrobial factors.

Reduction in intestinal colonization and invasion of internal organs after challenge by homologous and heterologous serovars of Salmonella enterica following vaccination of chickens with a novel trivalent inactivated Salmonella vaccine

A novel inactivated vaccine, comprising three serovars of Salmonella enterica (Enteritidis, serogroup O:9; Typhimurium, serogroup O:4; Infantis, serogroup O:7) grown under conditions of iron restriction and adjuvanted with aluminium hydroxide, was evaluated for efficacy following challenge by homologous and heterologous serovars. Chickens were vaccinated at 6 and 10 weeks of age by the intramuscular route and challenged 4 to 9 weeks after the second vaccination with serovars belonging to serogroup O:9 (Enteritidis), O:4 (Typhimurium and Heidelberg), O:7 (Infantis and Virchow), and O:8 (Hadar). All vaccinated birds produced a marked systemic antibody response against each of the component vaccine antigens by the time of challenge. Significant reductions in both colonization of the intestinal tract and invasion of internal organs were observed in vaccinated birds compared with non-vaccinated controls, irrespective of the challenge serovar. The findings suggest that broad serovar protection within the constitutive serogroups of an inactivated multi-valent vaccine is possible and could, therefore, play an important role in future Salmonella control programmes. RESEARCH HIGHLIGHTS Novel inactivated trivalent Salmonella chicken vaccine was developed and tested. Vaccine induced marked systemic antibody response against all vaccine antigens. Significant reductions in intestinal tract colonization and internal organ invasion. Vaccine efficacy demonstrated against homologous and heterologous serovars.

Egg-White Proteins Have a Minor Impact on the Bactericidal Action of Egg White Toward Salmonella Enteritidis at 45°C

Salmonella enterica serovar Enteritidis is noted for its ability to survive the harsh antibacterial activity of egg white which is presumed to explain its occurrence as the major food-borne pathogen associated with the consumption of eggs and egg products. Liquid egg white is a major ingredient for the food industry but, because of its thermal fragility, pasteurization is performed at the modest temperature of 57°C (for 2–6 min). Unfortunately, such treatment does not lead to sufficient reduction in S. Enteritidis contamination, which is a clear health concern when the product is consumed without cooking. However, egg white is able to limit S. Enteritidis growth due to its alkaline pH, iron deficiency and multiple antimicrobial proteins. This anti-Salmonella activity of egg white is temperature dependent and becomes bactericidal once the incubation temperature exceeds 42°C. This property is exploited in the highly promising pasteurization treatment (42–45°C for 1–5 days) which achieves complete killing of S. Enteritidis. However, the precise mechanism and the role of the egg-white proteins are not fully understood. Here, the impact of exposure of S. Enteritidis to egg white-based media, with or without egg-white proteins (>10 kDa), under bactericidal conditions (45°C) was explored by measuring survival and global expression. Surprisingly, the bactericidal activity of egg white at 45°C was only slightly affected by egg-white proteins indicating that they play a minor role in the bactericidal activity observed. Moreover, egg-white proteins had minimal impact on the global-gene-expression response to egg white such that very similar, major regulatory responses (20% genes affected) were observed both with and without egg-white proteins following incubation for 45 min at 45°C. Egg-white proteins caused a significant change in expression for just 64 genes, including the psp and lysozyme-inhibitor responses genes which is suggestive of an early membrane perturbation effect. Such damage was supported by disruption of the proton motive force by egg-white proteins. In summary, the results suggest that low-mass components of egg white are largely responsible for the bactericidal activity of egg white at 45°C.

Effects of dietary Bacillus subtilis RX7 and B2A supplementation on productive performance, egg quality, blood profiles, and excreta Salmonella counts in laying hens

An experiment was carried out to investigate the effect of Bacillus subtilis RX7 and B2A supplementation on egg production, egg quality, blood profile, and excreta Salmonella population in laying hens. A total of 192 Hy-Line Brown laying hens (40-wk-old) were randomly assigned into four dietary treatments, each of which was replicated eight times with six hens per replicate in a 5 wk trial. The dietary treatments were NC, which is a basal diet without antibiotics or Bacillus subtilis; PC, which is an NC + 0.5 g kg−1 antibiotic (virginiamycin) diet; BSR, which is an NC + 0.5 g kg−1 Bacillus subtilis RX7 (1.0 × 109 colony forming units g−1); and BSB, which is an NC + 0.5 g kg−1 Bacillus subtilis B2A (1.0 × 109 colony forming units g−1). The results showed that hens receiving BSB diets had increased (P < 0.05) eggshell thickness over hens fed the NC, PC, and BSR diets (week 3). The excreta Salmonella counts in the PC, BSR, and BSB groups were lower than the NC group (P < 0.05). These results indicate that dietary inclusion of Bacillus subtilis RX7 and B2A strains effectively decreased excreta Salmonella counts without any detrimental effects on the performance of laying hens.

Iron-Uptake Systems of Chicken-Associated Salmonella Serovars and Their Role in Colonizing the Avian Host

Iron is an essential micronutrient for most bacteria. Salmonella enterica strains, representing human and animal pathogens, have adopted several mechanisms to sequester iron from the environment depending on availability and source. Chickens act as a major reservoir for Salmonella enterica strains which can lead to outbreaks of human salmonellosis. In this review article we summarize the current understanding of the contribution of iron-uptake systems to the virulence of non-typhoidal S. enterica strains in colonizing chickens. We aim to address the gap in knowledge in this field, to help understand and define the interactions between S. enterica and these important hosts, in comparison to mammalian models.

Prevalence and antimicrobial susceptibility of Salmonella in the commercial eggs in China

Salmonellosis is a challenge to public health globally, and many infections have been principally linked to the consumption of contaminated eggs. The objective of this study is to estimate the prevalence of Salmonella in commercial eggs and susceptibilities of isolates to a panel of 14 antimicrobial agents which were determined according to Clinical and Laboratory Standards Institute (CSLI) procedures. A total of 33,288 eggs (5548 pooled samples of six eggs) were collected across China in 2016 and the prevalence of Salmonella was 0.5% (27/5548). The most predominant serotype was S. enteritidis. No significant differences were observed on the basis of the egg component tested, shell condition, packaging type, sampling site or sampling season. However, there were significant differences among provincial regions. About 64.3% (n = 18) isolates were resistant to nalidixic acid, followed by ampicillin (39.3%) and ampicillin/sulbactam (39.3%). All isolates were susceptible to ceftazidime, cefalothin, ciprofloxacin, cefepime, cefotaxime, imipenem and meropenem. Three Salmonella isolates exhibited resistance to multiple antibiotics. This study provides valuable baseline data of the occurrence of Salmonella in eggs, which will be used for risk assessments of possible human foodborne infections associated with the consumption of contaminated eggs.

Risk factors of Salmonella infection in laying hens in Menoua Division, Western region of Cameroon (Central Africa)

Salmonella infections in poultry farms are overlooked in many African countries; yet these infections are mostly zoonotic with impact on both poultry industry and public health. Considering the impact of Salmonella in laying hens, and the role of laying hens as a source of Salmonella outbreak in human, knowledge of the status of Salmonella on laying hen farms as well as the factors influencing the presence of Salmonella is important. In a cross sectional study, cloacal swabs were collected from 270 commercial laying hens on 27 farms located in Menoua Division. These samples were cultured on standard media. A questionnaire was used to collect information on animals, farms and farmer's characteristics. The prevalence of Salmonella was 93.34%; three zoonotic isolates namely S. Enteritidis (75.90%), S. Paratyphi (11.90%), and S. Typhimurium (5.60%) were identified. The location of farms was significantly associated with presence of Salmonella, and the risk of infection was 10-fold higher in Nkong-ni than Santchou (p < 0.05). Other potential risk factors such as flock size, age of the farm (infrastructure), or water source were not associated with Salmonella infection. The prophylactic measures against avian diseases in the country must include measures against Salmonella to protect poultry industry and public health.

The anti-bacterial iron-restriction defence mechanisms of egg white; the potential role of three lipocalin-like proteins in resistance against Salmonella

Salmonella enterica serovar Enteritidis (SE) is the most frequently-detected Salmonella in foodborne outbreaks in the European Union. Among such outbreaks, egg and egg products were identified as the most common vehicles of infection. Possibly, the major antibacterial property of egg white is iron restriction, which results from the presence of the iron-binding protein, ovotransferrin. To circumvent iron restriction, SE synthesise catecholate siderophores (i.e. enterobactin and salmochelin) that can chelate iron from host iron-binding proteins. Here, we highlight the role of lipocalin-like proteins found in egg white that could enhance egg-white iron restriction through sequestration of certain siderophores, including enterobactin. Indeed, it is now apparent that the egg-white lipocalin, Ex-FABP, can inhibit bacterial growth via its siderophore-binding capacity in vitro. However, it remains unclear whether Ex-FABP performs such a function in egg white or during bird infection. Regarding the two other lipocalins of egg white (Cal-γ and α-1-glycoprotein), there is currently no evidence to indicate that they sequester siderophores.

In vivo and in vitro evaluation of tissue colonization and survival capacity of Salmonella Oranienburg in laying hens

Salmonella enterica serovar Oranienburg (SO) was linked to a human salmonellosis outbreak in the Midwest in 2015 and 2016 from consumption of eggs. However, unlike Salmonella enterica serovar Enteritidis (SE), little is known regarding the potential of SO to colonize in laying hens and contaminate eggs. We used in vivo and in vitro models to evaluate tissue colonization and survival capacity of SO. Twenty eight-week-old laying hens were each challenged with an oral dose of approximately 107 (n = 92) or 109 (n = 96) colony-forming units (CFU) in 1 mL saline and evaluated after 1, 2, and 4 wk. Standard microbiological methods with pre-enrichment and enrichment in selective media were used for detection of SO in tissues, egg shell wash, internal egg contents, and excreta. Peak colonization of spleen (86.9%), ovaries (31.6%), upper oviduct (15.8%), and lower oviduct (34.3%) was detected between 1 and 2 wk post-infection (pi), while at 4 wk SO was only recovered from spleens (25%). Salmonella enterica serovar Oranienburg was not recovered from internal egg contents. However, the presence of SO on egg shells was seen when there were traces of excreta. Shedding in excreta was found in 92 and 100% birds gavaged with 107 and 109 CFU at 2 wk pi, respectively. The invasion and proliferation of SO in ovarian granulosa cells (GC) was compared to that of SE, and while the invasion of SO into GC was comparable to SE, proliferation of SO was significantly lower (P < 0.05). The infective potential of SO was also assessed by enumerating survival in egg white over 4 wk under refrigerated conditions, resulting in 65% survival at 4 wk. Overall, our data suggested that SO infection in layers did not result in egg contamination via vertical transmission, and colonization of egg-forming tissues was limited to 2 wk pi. Survival within GC and egg white demonstrates the ability of SO to withstand antibacterial factors and the potential of SO to penetrate the yolk.

Genomics of Salmonella contaminating backyard production systems reveals persistence and transmission of genetically related Salmonella on a farm basis

Animals raised in backyard productive systems (BPS) have been frequently associated with Salmonella outbreaks. Several serovars have caused these events, showing that different BPSs can be contaminated by distinct Salmonella serovars. The aim of this study was to characterize the genomic diversity of Salmonella isolates obtained from BPSs in Central Chile to understand their genomic relatedness. A whole-genome SNP-based phylogenetic analysis of 22 Salmonella isolates from 12 locations revealed that S. Typhimurium isolates clustered based on the BPS that they were originally isolated from, and the same was established for S. Enteritidis isolates. Furthermore, our genomic analysis shows that animals from different species (i.e., a chicken, a duck and a pig) carried genetically related S. Typhimurium strains within the same BPS. Moreover, some of these genetically related isolates were obtained in different years (2013 and 2014), indicating that farm-specific Salmonella can persist in BPSs for multiple years and that interspecies transmission is plausible in this environment. Understanding the dynamics of interspecies transmission of Salmonella serovars within a contaminated BPS is fundamental to the design of mitigation strategies to reduce outbreaks of human Salmonella associated with backyard production systems.

Comparative Genomic Analysis and Characterization of Two Salmonella enterica Serovar Enteritidis Isolates From Poultry With Notably Different Survival Abilities in Egg Whites

Salmonellaenterica serovar Enteritidis (Salmonella Enteritidis) is a globally important foodborne pathogen, and the contaminated chicken eggs are the major source of salmonellosis in humans. Salmonella Enteritidis strains are differentially susceptible to the hostile environment of egg whites. Strains with superior survival ability in egg whites are more likely to contaminate eggs and consequently infect humans. However, the genetic basis for this phenotype is unclear. We characterized two Salmonella Enteritidis strains isolated from chicken meat that had similar genetic backgrounds but large differences in survival ability in egg whites. Although genome comparisons indicated that the gene content and genomic synteny were highly conserved, variations including six insertions or deletions (INDELs) and 70 single nucleotide polymorphisms (SNPs) were observed between the two genomes. Of these, 38 variations including four INDELs and 34 non-synonymous SNPs (nsSNP) were annotated to result in amino acid substitutions or INDELs in coding proteins. These variations were located in 38 genes involved in lysozyme inhibition, vitamin biosynthesis, cell division and DNA damage response, osmotic and oxidative protection, iron-related functions, cell envelope maintenance, amino acid and carbohydrate metabolism, antimicrobial resistance, and type III secretion system. We carried out allelic replacements for two nsSNPs in bioC (biotin synthesis) and pliC (lysozyme inhibition), and two INDELs in ftsK and yqiJ (DNA damage response) by homologous recombination, and these replacements did not alter the bacterial survival ability in egg whites. However, the bacterial survival ability in egg whites was reduced when deletion mutation of the genes bioC and pliC occurred. This study provides initial correlations between observed genotypes and phenotypes and serves as an important caveat for further functional studies.

Multiplication in Egg Yolk and Survival in Egg Albumen of Genetically and Phenotypically Characterized Salmonella Enteritidis Strains

Prompt refrigeration of eggs to prevent the multiplication of Salmonella Enteritidis to high levels during storage is an important practice for reducing the risk of egg-transmitted human illness. The efficacy of egg refrigeration for achieving this goal depends on the interaction among the location of contamination, the ability of contaminant strains to survive or multiply, and the rate at which growth-restricting temperatures are attained. The present study assessed the significance of several characterized genetic and phenotypic properties for the capabilities of 10 Salmonella Enteritidis isolates to multiply rapidly in egg yolk and survive for several days in egg albumen during unrefrigerated (25°C) storage. The growth of small numbers of each Salmonella Enteritidis strain (approximately 10¹ CFU/mL) inoculated into egg yolk samples was determined after 6 and 24 h of incubation. The survival of larger numbers of Salmonella Enteritidis (approximately 10⁵ CFU/mL) inoculated into albumen samples was determined at 24 and 96 h of incubation. In yolk, the inoculated Salmonella Enteritidis strains multiplied to mean levels of approximately 10^2.6 CFU/mL after 6 h of incubation and 10^8.3 CFU/mL after 24 h. In albumen, mean levels of approximately 10^4.6 CFU/mL Salmonella Enteritidis were maintained through 96 h. The concentrations of the various Salmonella strains after incubation in either yolk or albumen were distributed over relatively narrow ranges of values. Significant ( P < 0.01) differences observed among individual strains suggested that maintenance of the fimbrial gene sefD may have positive genetic selection value by improving fitness to grow inside egg yolk, whereas the antibiotic resistance gene bla_TEM-1 tet(A) appeared to have negative genetic selection value by decreasing fitness to survive in egg albumen.

Frequency and Duration of Fecal Shedding of Salmonella Serovars Heidelberg and Typhimurium by Experimentally Infected Laying Hens Housed in Enriched Colony Cages at Different Stocking Densities

Eggs contaminated with Salmonella Enteritidis are leading sources of human salmonellosis, but Salmonella Heidelberg and Salmonella Typhimurium are also egg-associated pathogens. The management practices and housing facilities characterizing different systems for housing commercial egg flocks can influence Salmonella persistence and transmission. Animal welfare aspects of poultry housing have been widely debated, but their food safety ramifications are not thoroughly understood. The present study assessed the effects of two different bird stocking densities on the frequency and duration of fecal shedding of strains of Salmonella Heidelberg and Salmonella Typhimurium in groups of experimentally infected laying hens housed in colony cages enriched with perching and nesting areas. In separate trials, laying hens were distributed into two groups housed in enriched colony cages at stocking densities of 648 and 973 cm²/bird, and a third group was housed in conventional cages at 648 cm²/bird. All hens were orally inoculated with doses of 10⁸ colony-forming units (CFU) of either Salmonella Heidelberg or Salmonella Typhimurium. At eight weekly postinoculation intervals, samples of voided feces were collected from beneath each cage and cultured to detect Salmonella. Fecal shedding of Salmonella Heidelberg continued for 8 wk in all housing groups, but Salmonella Typhimurium shedding ceased after as little as 5 wk in enriched colony cages at low stocking density. After Salmonella Heidelberg infection, the overall frequency of positive fecal cultures for all sampling dates combined was significantly (P < 0.05) greater from either conventional cages (51.0%) or enriched colony cages (46.5%) at high stocking density than from enriched colony cages at low stocking density (33.3%). No significant differences in Salmonella Typhimurium fecal isolation were identified between housing groups. These results demonstrate that stocking density can affect intestinal colonization and fecal shedding in laying hens for some (but not necessarily all) Salmonella serovars or strains.

Recovery of Salmonella isolated from eggs and the commercial layer farms

BACKGROUND

Salmonella is recognized as a common bacterial cause of foodborne diarrheal illness worldwide, and animal or its food products have been the most common vehicles of the Salmonella infections. This study aimed to investigate the distribution of Salmonella in two commercial layer farms and to determine the genetic relatedness between these strains. The Salmonella isolates were serotyped by slide agglutination using commercial antisera and analyzed for genetic relatedness using pulsed-field gel electrophoresis (PFGE).

RESULTS

The internal environment had the highest prevalence of Salmonella (14/15, 93.3%), followed by external environment (60/96, 62.5%) and egg samples (23/84, 27.3%). The prevalence of Salmonella in the environment was significantly higher than that in egg samples (p < 0.05). The occurrence of Salmonella in the internal environment (93.3%) was relatively higher than in the external environment (55.6-77.2%). The 111 isolates were distributed among 15 PFGE types, and the PFGE results suggested that there existed cross-contamination between these strains not only from eggs, but also from the environments.

CONCLUSIONS

The findings indicated ongoing Salmonella cross-contamination inside or outside of the layer farms, and that Salmonella could also spread along the egg production line.

Evaluation of the effectiveness and safety of a genetically modified live vaccine in broilers challenged with Salmonella Heidelberg

Salmonellosis ranks among the major diseases of commercial poultry, and its presence in poultry flocks is responsible for economic losses and risks related to public health. Vaccines are an important tool within integrated programmes to control salmonellosis. The purpose of this study was to assess cross-protection provided by the Poulvac® ST vaccine in the control of Salmonella Heidelberg in experimentally challenged 3- and 21-day-old birds. Eighty birds were identified and separated into four treatments (T1: vaccinated and challenged at 3 days of age, T2: unvaccinated and challenged at 3 days of age, T3: vaccinated and challenged at 21 days of age, and T4: unvaccinated and challenged at 21 days of age). The inoculum was produced from a Brazilian field strain of SH. At the end of the experiment, caecum and liver/spleen samples were collected for quantitative and qualitative analysis of SH, respectively. Analysis of the liver/spleen showed that Poulvac® ST significantly (P ≤ 0.05) reduced the percentage of SH positivity in the group challenged at 3 days of age, while in the group challenged at 21 days this difference was almost considered significant (P = 0.1818). On the other hand, there was no statistically significant difference in SH count in the caecum (CFU/g) in the group challenged at 3 days, but for the group challenged at 21 days the SH counts were significantly (P ≤ 0.05) lower in the vaccinated group when compared to the positive control.

Global Gene-expression Analysis of the Response of Salmonella Enteritidis to Egg White Exposure Reveals Multiple Egg White-imposed Stress Responses

Chicken egg white protects the embryo from bacterial invaders by presenting an assortment of antagonistic activities that combine together to both kill and inhibit growth. The key features of the egg white anti-bacterial system are iron restriction, high pH, antibacterial peptides and proteins, and viscosity. Salmonella enterica serovar Enteritidis is the major pathogen responsible for egg-borne infection in humans, which is partly explained by its exceptional capacity for survival under the harsh conditions encountered within egg white. However, at temperatures up to 42°C, egg white exerts a much stronger bactericidal effect on S. Enteritidis than at lower temperatures, although the mechanism of egg white-induced killing is only partly understood. Here, for the first time, the impact of exposure of S. Enteritidis to egg white under bactericidal conditions (45°C) is explored by global-expression analysis. A large-scale (18.7% of genome) shift in transcription is revealed suggesting major changes in specific aspects of S. Enteritidis physiology: induction of egg white related stress-responses (envelope damage, exposure to heat and alkalinity, and translation shutdown); shift in energy metabolism from respiration to fermentation; and enhanced micronutrient provision (due to iron and biotin restriction). Little evidence of DNA damage or redox stress was obtained. Instead, data are consistent with envelope damage resulting in cell death by lysis. A surprise was the high degree of induction of hexonate/hexuronate utilization genes, despite no evidence indicating the presence of these substrates in egg white.

Feed Supplementation with Red Seaweeds, Chondrus crispus and Sarcodiotheca gaudichaudii, Reduce Salmonella Enteritidis in Laying Hens

Salmonella Enteritidis is vertically transmitted to eggs from laying hens through infected ovaries and oviducts. S. Enteritidis can also penetrate the eggshell from contaminated feces. Reducing S. Enteritidis in laying hens is vital to provide safer eggs and minimize the spread of salmonellosis to humans. Antibiotics have been widely used to control bacterial diseases in broilers and laying hens. However, there is a major concern that the use of antibiotics leads to the development of antibiotic resistance and adverse effects on microbiota of the treated birds. Thus, there is an interest in developing alternatives to antibiotics, such as dietary prebiotics. In the present study, feed supplemented with the red seaweeds: Chondrus crispus (CC) or Sarcodiotheca gaudichaudii (SG), was offered to laying hens late in production to control S. Enteritidis. Diets contained one of the following; 2% or 4% Chondrus crispus (CC2, and CC4, respectively) or Sarcodiotheca gaudichaudii (SG2 and SG4, respectively). Chlortetracycline was used in the positive control diet. During week-4, 48 birds were orally challenged with 2 × 109 CFU/mL of S. Enteritidis. Eggs and fecal samples were collected 1, 3, 5, and 7 days' post inoculation. Birds were euthanized and organs (ceca, ovary, liver, and spleen) were sampled and analyzed for the presence of S. Enteritidis, 7 days' post inoculation. Results showed that seaweed reduced the negative effect on body weight and egg production in S. Enteritidis-challenged laying hens. Analysis of fecal samples showed that the antibiotic (CTC) reduced S. Enteritidis in the intestinal tract and fecal samples, 3 days' post inoculation. Fecal samples from Chlortetracycline and CC4 supplemented birds tested negative for S. Enteritidis on days 5 and 7 post inoculation (lowest detection limit = 10-1). S. Enteritidis colonization in the ceca was also significantly reduced in birds fed CC (4%) and Chlortetracycline. Blood serum profiles revealed that there were no significant differences in serum aspartate aminotransferase (AST) and sodium. However, the level of serum immunoglobulin (IgA) was higher in the CC4 treatment. The relative abundance of Lactobacillus acidophilus was significantly higher in CC4 while, the abundance of the pathogenic bacteria, Clostridium perfringens and Salmonella Enteritidis were reduced compared to control. Results indicate that feed supplemented with 4% CC is effective in providing protection against Salmonella Enteritidis colonization in laying hens.

Salmonella Enteritidis flagellar mutants have a colonization benefit in the chicken oviduct

Egg borne Salmonella Enteritidis is still a major cause of human food poisoning. Eggs can become internally contaminated following colonization of the hen's oviduct. In this paper we aimed to analyze the role of flagella of Salmonella Enteritidis in colonization of the hen's oviduct. Using a transposon library screen we showed that mutants lacking functional flagella are significantly more efficient in colonizing the hen's oviduct in vivo. A micro-array analysis proved that transcription of a number of flagellar genes is down-regulated inside chicken oviduct cells. Flagella contain flagellin, a pathogen associated molecular pattern known to bind to Toll-like receptor 5, activating a pro-inflammatory cascade. In vitro tests using primary oviduct cells showed that flagellin is not involved in invasion. Using a ligated loop model, a diminished inflammatory reaction was seen in the oviduct resulting from injection of an aflagellated mutant compared to the wild-type. It is hypothesized that Salmonella Enteritidis downregulates flagellar gene expression in the oviduct and consequently prevents a flagellin-induced inflammatory response, thereby increasing its oviduct colonization efficiency.

Genetic Basis of Salmonella Enteritidis Pathogenesis in Chickens

Salmonella Enteritidis (SE) is the predominant cause of the food-borne salmonellosis in humans, in part because this serotype has the unique ability to contaminate chicken eggs without causing discernible illness in the infected birds. Attempts to develop effective vaccines and eradicate SE from chickens are undermined by significant limitations in our current understanding of the genetic basis of pathogenesis of SE in this reservoir host. In this chapter, we summarize the infection kinetics and provide an overview of the current understanding of genetic factors underlying SE infection in the chicken host. We also discuss the important knowledge gaps that, if addressed, will improve our understanding of the complex biology of SE in young chickens and in egg laying hens.

Tissue colonization and circulating T lymphocytes in laying hens upon oral challenge with Salmonella enterica serovars

Evaluating the potential of Salmonella serovars for tissue colonization and egg contamination in laying hens is critical due to widespread consumption of poultry and egg-containing products. The 2009 FDA Egg Rule was implemented to target the eradication of Salmonella enterica Enteritidis (SE) from layers; however, other Salmonella serovars, such as Heidelberg (SH) and Typhimurium (ST), have also been associated with poultry-related outbreaks. We conducted this study to see if serovars other than SE could colonize in laying hens, cause egg contamination, and modulate circulating T-cell populations. Laying hens were orally gavaged with 10⁷ colony forming units (CFU) of SE, SH, or ST and assessed for colonization in spleen, ovaries, and oviduct 10 d postchallenge. Splenic colonization was similar for all the serovars; however, colonization of ovaries and oviducts was significantly higher with SH compared to SE and ST. Furthermore, SH challenge resulted in egg contamination, while SE and ST did not result in contaminated eggs. Phenotypic evaluation of peripheral blood lymphocytes showed significant reduction in CD4 cells in SH-challenged birds and lower CD8α and CD8β cells in SE-challenged birds compared to controls. Our data showed that non-SE serovars have equal or higher potential to colonize reproductive tissues of laying hens and may be accompanied by altered lymphocyte populations.

Higher Storage Temperature Causes Greater Salmonella enterica Serovar Typhimurium Internal Penetration of Artificially Contaminated, Commercially Available, Washed Free Range Eggs

Foodborne salmonellosis is a major public health concern, with contaminated eggs identified as a significant source of infection. In Australia, the most prevalent cause of salmonellosis from eggs is Salmonella enterica subsp. enterica serovar Typhimurium. This study explored the effect of temperature after 1, 7, 14, 21, and 28 days of storage on commercially available washed free range eggs, artificially contaminated with Salmonella Typhimurium on the external surface. At each time point, the external surface of the egg, the crushed eggshell, and the internal egg yolk and albumen were analyzed for Salmonella. After 28 days of storage, 25% of eggs stored at 4°C, 50% of eggs stored at 14°C, and 100% of eggs stored at 23 and 35°C were internally contaminated with Salmonella. After 1 day of storage, more than 50% of all eggs had Salmonella present in the crushed shell after the external surface had been disinfected with ethanol. This is the first study to demonstrate that refrigeration reduced the potential for Salmonella Typhimurium to penetrate the eggshell membrane and internally contaminate table eggs commercially available in Australia. It also suggests that the processes of cracking eggs may be a source of cross-contamination within the kitchen.

Study of Salmonella Typhimurium Infection in Laying Hens

Members of Salmonella enterica are frequently involved in egg and egg product related human food poisoning outbreaks worldwide. In Australia, Salmonella Typhimurium is frequently involved in egg and egg product related foodborne illness and Salmonella Mbandaka has also been found to be a contaminant of the layer farm environment. The ability possessed by Salmonella Enteritidis to colonize reproductive organs and contaminate developing eggs has been well-described. However, there are few studies investigating this ability for Salmonella Typhimurium. The hypothesis of this study was that the Salmonella Typhimurium can colonize the gut for a prolonged period of time and that horizontal infection through feces is the main route of egg contamination. At 14 weeks of age hens were orally infected with either S. Typhimurium PT 9 or S. Typhimurium PT 9 and Salmonella Mbandaka. Salmonella shedding in feces and eggs was monitored for 15 weeks post-infection. Egg shell surface and internal contents of eggs laid by infected hens were cultured independently for detection of Salmonella spp. The mean Salmonella load in feces ranged from 1.54 to 63.35 and 0.31 to 98.38 most probable number/g (MPN/g) in the S. Typhimurium and S. Typhimurium + S. Mbandaka group, respectively. No correlation was found between mean fecal Salmonella load and frequency of egg shell contamination. Egg shell contamination was higher in S. Typhimurium + S. Mbandaka infected group (7.2% S. Typhimurium, 14.1% S. Mbandaka) compared to birds infected with S. Typhimurium (5.66%) however, co-infection had no significant impact on egg contamination by S. Typhimurium. Throughout the study Salmonella was not recovered from internal contents of eggs laid by hens. Salmonella was isolated from different segments of oviduct of hens from both the groups, however pathology was not observed on microscopic examination. This study investigated Salmonella shedding for up to 15 weeks p.i which is a longer period of time compared to previously published studies. The findings of current study demonstrated intermittent but persistent fecal shedding of Salmonella after oral infection for up to 15 weeks p.i. Further, egg shell contamination, with lack of internal egg content contamination and the low frequency of reproductive organ infection suggested that horizontal infection through contaminated feces is the main route of egg contamination with S. Typhimurium in laying hens.

Egg white versus Salmonella Enteritidis! A harsh medium meets a resilient pathogen

Salmonella enterica serovar Enteritidis is the prevalent egg-product-related food-borne pathogen. The egg-contamination capacity of S. Enteritidis includes its exceptional survival capability within the harsh conditions provided by egg white. Egg white proteins, such as lysozyme and ovotransferrin, are well known to play important roles in defence against bacterial invaders. Indeed, several additional minor proteins and peptides have recently been found to play known or potential roles in protection against bacterial contamination. However, although such antibacterial proteins are well studied, little is known about their efficacy under the environmental conditions prevalent in egg white. Thus, the influence of factors such as temperature, alkalinity, nutrient restriction, viscosity and cooperative interactions on the activities of antibacterial proteins in egg white remains unclear. This review critically assesses the available evidence on the antimicrobial components of egg white. In addition, mechanisms employed by S. Enteritidis to resist egg white exposure are also considered along with various genetic studies that have shed light upon egg white resistance systems. We also consider how multiple, antibacterial proteins operate in association with specific environmental factors within egg white to generate a lethal protective cocktail that preserves sterility.

Avaliação da resposta imunológica da mucosa intestinal de frangos de corte desafiados com diferentes sorovares de Salmonella

Objetivou-se com o presente estudo comparar o efeito de diferentes sorovares de Salmonella na resposta imune local da mucosa do intestino de frangos de corte. Aos sete dias de idade, as aves foram desafiadas com os sorovares S. Enteritidis, S. Typhimurium, S. Senftenberg, S. Mbandaka e S. Minnesota. Foi observado que todos os sorovares testados foram capazes de colonizar o intestino das aves sendo possível o isolamento de Salmonella em suabes de cloaca, 48 h após inoculação. De maneira geral, as aves do grupo controle negativo, que não foram desafiados apresentaram quantidade significativamente menor de células imunológicas na mucosa intestinal do que as aves desafiadas. Porém, verificou-se que os sorovares de Salmonella, utilizados neste estudo, apresentaram diferentes efeitos sobre a dinâmica celular da mucosa do íleo e ceco e afetaram de modo diferente o ganho de peso e ganho médio diário das aves demonstrando distintos graus de patogenicidade. Os sorovares Enteritidis e Typhimurium apresentaram um efeito mais intenso tanto no desempenho quanto na mobilização de células imunológicas na mucosa intestinal de frangos de corte

Salmonella and eggs: from production to plate

Salmonella contamination of eggs and egg shells has been identified as a public health concern worldwide. A recent shift in consumer preferences has impacted on the egg industry, with a push for cage-free egg production methods. There has also been an increased desire from consumers for raw and unprocessed foods, potentially increasing the risk of salmonellosis. In response to these changes, this review explores the current literature regarding Salmonella contamination of eggs during the production processing through to food handling protocols. The contamination of eggs with Salmonella during the production process is a complex issue, influenced by many variables including flock size, flock age, stress, feed, vaccination, and cleaning routines. Currently there is no consensus regarding the impact of caged, barn and free range egg production has on Salmonella contamination of eggs. The literature regarding the management and control strategies post-collection, during storage, transport and food handling is also reviewed. Pasteurisation and irradiation were identified as the only certain methods for controlling Salmonella and are essential for the protection of high risk groups, whereas control of temperature and pH were identified as potential control methods to minimise the risk for foods containing raw eggs; however, further research is required to provide more detailed control protocols and education programs to reduce the risk of salmonellosis from egg consumption.

Salmonella Virchow Infection of the Chicken Elicits Cellular and Humoral Systemic and Mucosal Responses, but Limited Protection to Homologous or Heterologous Re-Challenge

Salmonella enterica serovar Virchow usually causes mild gastroenteritis in humans; however, it is frequently invasive and many isolates are resistant to a broad-range of therapeutic antimicrobials. Poultry meat is considered a major source of human infection. In this study, we characterize the infection biology and immune response to S. Virchow in chickens and determine protection against homologous and heterologous re-challenge, with S. Virchow or S. Typhimurium. Following oral infection of 7-day-old chickens, S. Virchow colonized the gastrointestinal tract and the spleen. Infection elicited an increase in specific IgA, IgG, and IgM antibodies and relative quantitative changes in several leukocyte populations, including CD3, CD4, CD8α, CD8β, MHC II, KuL01, and γδ TCR positive cells, both in the gastrointestinal tract and systemically. Increased expression of pro-inflammatory cytokines IL-1β and IL-6 and the chemokine CXCLi2 was also found. Primary infection with S. Virchow offered limited systemic protection against re-challenge with S. Virchow or S. Typhimurium, but no protection against cecal colonization. In conclusion, S. Virchow exhibits similar infection biology and immune responses in the chicken to that previously described for S. Typhimurium. Unlike S. Typhimurium, S. Virchow infection is poorly protective to homologous and heterologous re-challenge. These findings suggest that S. Virchow is capable of colonizing the chicken well and therefore, presents a risk of entering the food chain in meat production. Furthermore, the development of vaccines that protect effectively against S. Virchow and indeed multivalent vaccines that protect across all Salmonella serogroups in the chicken would appear to remain a challenging proposition.

Microarray-based detection of Salmonella enterica serovar Enteritidis genes involved in chicken reproductive tract colonization

Salmonella enterica serovar Enteritidis has developed the potential to contaminate table eggs internally, by colonization of the chicken reproductive tract and internalization in the forming egg. The serotype Enteritidis has developed mechanisms to colonize the chicken oviduct more successfully than other serotypes. Until now, the strategies exploited by Salmonella Enteritidis to do so have remained largely unknown. For that reason, a microarray-based transposon library screen was used to identify genes that are essential for the persistence of Salmonella Enteritidis inside primary chicken oviduct gland cells in vitro and inside the reproductive tract in vivo. A total of 81 genes with a potential role in persistence in both the oviduct cells and the oviduct tissue were identified. Major groups of importance include the Salmonella pathogenicity islands 1 and 2, genes involved in stress responses, cell wall, and lipopolysaccharide structure, and the region-of-difference genomic islands 9, 21, and 40.

An immunogenic Salmonella ghost confers protection against internal organ colonization and egg contamination

The tightly regulated expression of the PhiX174 lysis gene E from a multi-copy plasmid led to the stable production of an Salmonella Enteritidis bacterial ghost. The present study was conducted to evaluate induction of the humoral and cell-mediated immune responses induced after single or double intramuscular immunization with the S. Enteritidis ghost and to assess its protective effect on colonization of the intestinal tract, visceral and reproductive organs, internal egg contamination, and egg production of laying chickens. A total of 60 chickens were equally divided into three groups (n=20); group A (non-immunized control), group B (immunized at 8 and 16 weeks of age) and group C (immunized at 16th week of age). Chickens from both immunized groups B and C demonstrated significant increases in plasma IgG, intestinal secretory IgA levels, and antigen-specific lymphocyte proliferative responses. The population of CD3+CD4+ positive T cells in the immunized chickens was also significantly increased after immunization and virulent challenge. In addition, the immunized groups B and C showed significantly higher egg production and a lower percentage of S. Enteritidis contaminated eggs after challenge compared to those of group A. A comparison of challenge strain isolation from the immunized-challenged and non-immunized-challenged layer hens showed that the double immunization group induced excellent protection against intestinal, liver, splenic, and ovarian Salmonella colonization; however, the single immunized chickens showed lower counts only in the splenic and ovarian organs. Overall, the data give compelling evidence that vaccination with the S. Enteritidis ghost induced robust protective immunity against experimental avian salmonellosis and may contribute to the reduce incidence of egg contamination.

A genome-wide screen identifies Salmonella Enteritidis lipopolysaccharide biosynthesis and the HtrA heat shock protein as crucial factors involved in egg white persistence at chicken body temperature

Eggs contaminated with Salmonella Enteritidis are an important source of human foodborne Salmonella infections. Salmonella Enteritidis is able to contaminate egg white during formation of the egg within the chicken oviduct, and it has developed strategies to withstand the antimicrobial properties of egg white to survive in this hostile environment. The mechanisms involved in the persistence of Salmonella Enteritidis in egg white are likely to be complex. To address this issue, a microarray-based transposon library screen was performed to identify genes necessary for survival of Salmonella Enteritidis in egg white at chicken body temperature. The majority of identified genes belonged to the lipopolysaccharide biosynthesis pathway. Additionally, we provide evidence that the serine protease/heat shock protein (HtrA) appears essential for the survival of Salmonella Enteritidis in egg white at chicken body temperature.

The influences of SE infection on layers' production performance, egg quality and blood biochemical indicators

BACKGROUND

Salmonella enterica serovar Enteritidis (SE), as a major cause of foodborn illness, infects humans mainly through the egg. However, the symptom of laying hens usually is not typical and hard to diagnosis. In the present study, it is studied that the influences of SE infection on layers' performance, egg quality and blood biochemical indicators. It will help us to improve the strategy to control SE infection in commercial layers. One hundred layers at 20 wk of age were divided into 2 groups, 60 hens for experiment and others for control. The experiment group was fed with the dosage of 108 CFU SE per hen. The specific PCR was used to detect the deposition of SE. On the 8 d after SE infection, 10 hens from the control group and 30 hens from the experimental group were slaughtered to detect the SE colonization. The production performance, egg quality and blood biochemical indices were also analyzed.

RESULTS

The results showed that the colonization rate of SE was highest in caecum contents (55.17%) and lowest in vagina (17.24%). For the eggs the detection rate of SE was highest on the eggshell (80.00%) and lowest in yolk (18.81%). SE infection had no significant influence on production performance and egg qualities (P > 0.05). The difference of laying rate between the experimental and control groups was less than 0.30%, and both were approximately equal to 82.00%. The blood analysis showed that the aspartic aminotransferase (AST) and alanine aminotransferase (ALT) of experimental group was significantly higher than those of control group (P < 0.05). For experimental and control groups AST values were 236.22 U/l and 211.84 U/l respectively, and ALT values were 32.19 U/l and 24.55 U/l. All of coefficients were less than 20%. The colonization of SE in organs increases the enzyme activities of AST and ALT in blood.

CONCLUSIONS

SE in feed could invade the oviduct and infect the forming eggs. It significantly increased the concentration of ALT and AST in blood. However,SE infection was hard to be observed from the appearances of layer and egg. It might be a dangerous risk to human health.

Salmonella Enteritidis is superior in egg white survival compared with other Salmonella serotypes

Salmonella enterica subspecies enterica serotype Enteritidis is a major cause of egg-borne human salmonellosis. The ability to survive in egg albumen at chicken body temperature was hypothesized to be an important factor involved in the predominant contamination of eggs by this specific serotype. Eighty-nine Salmonella strains from different serotypes, belonging to 5 serogroups, were incubated for 24 h in egg white at 42°C. The number of Salmonella Enteritidis strains that were able to survive in egg white was significantly higher compared with strains belonging to other serotypes and serogroups that were tested in this study. These data add evidence to the hypothesis that egg white survival is one of the reasons why Salmonella Enteritidis is more predominantly isolated from contaminated eggs, and helps explaining why most reported egg-borne Salmonella outbreaks in humans are caused by Salmonella Enteritidis.