Evaluation of resistance of four strains of commercial laying hens to experimental infection with Salmonella enteritidis phage type eight

Epigenetic modification of TLRs in leukocytes is associated with increased susceptibility to Salmonella enteritidis in chickens

Toll-like receptors (TLRs) signaling pathways are the first lines in defense against Salmonella enteritidis (S. enteritidis) infection but the molecular mechanism underlying susceptibility to S. enteritidis infection in chicken remains unclear. SPF chickens injected with S. enteritidis were partitioned into two groups, one consisted of those from Salmonella-susceptible chickens (died within 5 d after injection, n = 6), the other consisted of six Salmonella-resistant chickens that survived for 15 d after injection. The present study shows that the bacterial load in susceptible chickens was significantly higher than that in resistant chickens and TLR4, TLR2-1 and TLR21 expression was strongly diminished in the leukocytes of susceptible chickens compared with those of resistant chickens. The induction of expression of pro-inflammatory cytokine genes, IL-6 and IFN-β, was greatly enhanced in the resistant but not in susceptible chickens. Contrasting with the reduced expression of TLR genes, those of the zinc finger protein 493 (ZNF493) gene and Toll-interacting protein (TOLLIP) gene were enhanced in the susceptible chickens. Finally, the expression of TLR4 in peripheral blood mononuclear cells (PBMCs) infected in vitro with S. enteritidis increased significantly as a result of treatment with 5-Aza-2-deoxycytidine (5-Aza-dc) while either 5-Aza-dc or trichostatin A was effective in up-regulating the expression of TLR21 and TLR2-1. DNA methylation, in the predicted promoter region of TLR4 and TLR21 genes, and an exonic CpG island of the TLR2-1 gene was significantly higher in the susceptible chickens than in resistant chickens. Taken together, the results demonstrate that ZNF493-related epigenetic modification in leukocytes probably accounts for increased susceptibility to S. enteritidis in chickens by diminishing the expression and response of TLR4, TLR21 and TLR2-1.

Genetic control of resistance to salmonellosis and to Salmonella carrier-state in fowl: a review

Salmonellosis is a frequent disease in poultry stocks, caused by several serotypes of the bacterial species Salmonella enterica and sometimes transmitted to humans through the consumption of contaminated meat or eggs. Symptom-free carriers of the bacteria contribute greatly to the propagation of the disease in poultry stocks. So far, several candidate genes and quantitative trait loci (QTL) for resistance to carrier state or to acute disease have been identified using artificial infection of S. enterica serovar Enteritidis or S. enterica serovar Typhimurium strains in diverse genetic backgrounds, with several different infection procedures and phenotypic assessment protocols. This diversity in experimental conditions has led to a complex sum of results, but allows a more complete description of the disease. Comparisons among studies show that genes controlling resistance to Salmonella differ according to the chicken line studied, the trait assessed and the chicken's age. The loci identified are located on 25 of the 38 chicken autosomal chromosomes. Some of these loci are clustered in several genomic regions, indicating the possibility of a common genetic control for different models. In particular, the genomic regions carrying the candidate genes TLR4 and SLC11A1, the Major Histocompatibility Complex (MHC) and the QTL SAL1 are interesting for more in-depth studies. This article reviews the main Salmonella infection models and chicken lines studied under a historical perspective and then the candidate genes and QTL identified so far.

QTL for resistance to Salmonella carrier state confirmed in both experimental and commercial chicken lines

The ability of chickens to carry Salmonella without displaying disease symptoms is responsible for Salmonella propagation in poultry stocks and for subsequent human contamination through the consumption of contaminated eggs or meat. The selection of animals more resistant to carrier state might be a way to decrease the propagation of Salmonella in poultry stocks and its transmission to humans. Five QTL controlling variation for resistance to carrier state in a chicken F(2) progeny derived from the White Leghorn inbred lines N and 6(1) had been previously identified using a selective genotyping approach. Here, a second analysis on the whole progeny was performed, which led to the confirmation of two QTL on chromosomes 2 and 16. To assess the utility of these genomic regions for selection in commercial lines, we tested them together with other QTL identified in an [Nx6(1)] x N backcross progeny and with the candidate genes SLC11A1 and TLR4. We used a commercial line divergently selected for either low or high carrier-state resistance both in young chicks and in adult hens. In divergent chick lines, one QTL on chromosome 1 and one in the SLC11A1 region were significantly associated with carrier-state resistance variations; in divergent adult lines, one QTL located in the major histocompatibility complex on chromosome 16 and one in the SLC11A1 region were involved in these variations. Genetic studies conducted on experimental lines can therefore be of potential interest for marker-assisted selection in commercial lines.

Intermittent long-term shedding and induction of carrier birds after infection of chickens early posthatch with a low or high dose of Salmonella enteritidis

Poultry are very likely to become infected with Salmonella in the early posthatch period, due to environmental contamination. The purpose of this study was to evaluate the effect of infection dose on the risk of persistent infection in laying hens. In this study, young layer chicks were orally infected with a low (10(2) at 1 d posthatch) or a high dose (10(9) cfu at 1 wk posthatch) of Salmonella Enteritidis. The pattern and duration of fecal shedding was studied for 18 wk. All chickens shed Salmonella early after infection and shed Salmonella intermittently during the whole study period. There were more positive birds in the high-dose group than in the low-dose group in the first weeks following Salmonella exposure. From 10 wk postinfection onwards, however, birds that were orally infected with the low dose of Salmonella Enteritidis shed more Salmonella than the birds that received the high dose. At 18 wk of age, there was no difference in cecal colonization between the treatment groups. It can be concluded that infection of newly hatched chicks with a low dose of Salmonella Enteritidis can lead to persistent infection until onset of lay, hereby excreting Salmonella bacteria intermittently.

Descriptive Study of California Egg Layer Premises and Analysis of Risk Factors for Salmonella enterica serotype enteritidis as Characterized by Manure Drag Swabs

This cross-sectional, double-blind study reports the prevalence of Salmonella enterica serotype enteritidis (SE) on California egg layer premises using single vs. pooled manure drag swabs and presents a description of egg production and management systems in the state and an initial analysis of risk factors for SE. The study included 91% of all known eligible egg premises in California, representing the majority of eggs produced in the state. The overall prevalence of SE on California egg layer premises was 10.5%, while 1.1% of all rows sampled were positive for SE. The percentage of positive rows for SE on any premises never exceeded 25% of the 16 swabs collected per premises. A description of egg production and management on California egg layer premises is presented. Statistically significant associations for SE were not evident and were limited because of sample size and the low prevalence of SE on California egg layer premises. Several biological and management factors, such as flock health, stage of production, manure management, ventilation, and watering systems, show trend associations with premises positive for SE and require further investigation. Manure drag swabs serve as a useful tool to validate the core components of an egg quality assurance program for SE based on process control principles.

Association of twelve candidate gene polymorphisms and response to challenge with Salmonella enteritidis in poultry

Breeding for disease resistance to Salmonella enteritidis (SE) could be an effective approach to control Salmonella in poultry. The candidate gene approach is a useful method to investigate genes that are involved in genetic resistance. In this study, 12 candidate genes that are involved in the pathogenesis of Salmonella infection were investigated using five different genetic groups of meat-type chicken. The genes were natural resistance associated macrophage protein 1 (SLC11A1, previously known as NRAMP1), inhibitor of apoptosis protein 1 (IAP1), prosaposin (PSAP), Caspase-1 (CASP1), inducible nitric oxide production (iNOS), interferon-gamma (IFNG), interleukin-2 (IL2), immunoglobulin light chain (IGL), ZOV3, and transforming growth factors B2, B3 and B4 (TGFB2, B3 and B4). In total, 117 birds of all groups were challenged with SE at the age of 3 weeks. In all birds at 7-day post-infection SE load in caecum content, spleen and liver were quantified. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assays were used to genotype all animals for each gene. Overall we found the most significant associations with caecum content, nine of 12 genes showed a significant association (SLC11A1, IAP1, PSAP, CASP1, iNOS, IL2, IGL, TGFB2 and TGFB4). For liver, five genes (SLC11A1, CASP1, IL2, IGL, and TGFB4) and for spleen, only one gene (TGFB3) showed a significant association with SE load. By showing associations of 12 PCR-RFLP assays with SE load after a pathogen challenge, this study confirmed the polygenic nature of disease resistance to SE.

Resistance of broiler outbred lines to infection with Salmonella enteritidis

Salmonella infections originating from poultry are one of the major causes of food-borne disease. For the control of salmonella in poultry a multifactorial approach is more likely to be effective, and the genetic resistance of poultry breeds to salmonella infections may be a valuable contribution. Experimental Salmonella enteritidis infections were examined in three different broiler outbred lines: the FC line, which had been selected for feed conversion efficiency; the R line, which had been selected for growth rate; and the C line, a commercially available line. The FC line had the highest mortality rate after intramuscular inoculation with 5 x 10(6) colony forming units (CFU) of S. enteritidis at 2 weeks of age (40% versus 21 and 20% in the other lines). However, at slaughter age, the number of birds carrying salmonella in caecal contents, and the concentration of salmonella in the caecal contents, was lowest in the FC line. The FC and R lines were compared by inoculation with doses ranging from 10(2) to 10(7) CFU S. enteritidis. At sublethal doses (10(5) CFU or less), the FC line carried significantly less salmonella in caecal contents and the rate of systemic infection was lower. The start of shedding was also delayed compared with the R line. At doses of 10(6) CFU S. enteritidis or higher, there were no differences in salmonella carriage between the lines, and the FC line showed higher mortality. In conclusion, resistance to mortality and resistance to the carriage of S. enteritidis do not necessarily coincide within lines, as the FC line showed high mortality but low carriage, both in survivors of high infection doses and in all birds at lower infection doses.

Salmonella enterica serovar enteritidis burden in broiler breeder chicks genetically associated with vaccine antibody response

The relationship between antibody response to Salmonella enteritidis vaccine and internal organ burden of S. enteritidis is not fully understood. The genetic relationship, therefore, between postchallenge S. enteritidis burden and antibody response to S. enteritidis vaccine was determined in broiler breeder chicks. Sibling chicks from a broiler breeder male line were either inoculated with a pathogenic S. enteritidis or vaccinated with a commercial S. enteritidis vaccine. Spleen, liver, cecal wall, and cecal content samples from S. enteritidis-challenged chicks (n = 120) were cultured for enumeration of bacteria. Unchallenged chicks (n = 314) were vaccinated at 11 days of age, and serum samples were taken at 10 days postvaccination. Antibody response to vaccination and number of S. enteritidis in cecal content cultures were negatively correlated (-0.772), demonstrating that genetic potential for greater antibody response to S. enteritidis vaccine is associated with lesser S. enteritidis bacterial burden in cecal content of broiler breeder chicks. The findings suggest that genetic selection for vaccine antibody responsiveness can lower bacterial burden in the gut lumenal content and, thus, potentially reduce contamination of poultry products at processing.

Genetic line differences in survival and pathogen load in young layer chicks after Salmonella enterica serovar enteritidis exposure

Early infection may result in long-term colonization of layers with Salmonella enterica sv. enteritidis (S. enteritidis, SE), resulting in shedding into table or hatching eggs. To evaluate genetic factors underlying early response to SE, genetic line differences in mortality and pathogen load at two sites (cecal lumen and spleen) were investigated. At day of hatch, chicks of four genetic lines were intra-esophageally inoculated with one of three doses of SE phage type 13a. There was a significant effect (P < 0.001) of genetic line on chick 6-d survival. The effect of genetic line was significant (P < 0.05) on survivors' SE burden in cecal content but not on SE burden per gram of spleen. The SE pathogen load of the spleen and the cecal content were not significantly correlated, indicating that independent host mechanisms are partly responsible for these two traits. Genetic line differences in chick survival and SE colonization of cecal content were demonstrated in young layer chicks.

Characterization of the innate and adaptive immunity to Salmonella enteritidis PT1 infection in four broiler lines

Four broiler lines were inoculated orally with Salmonella enteritidis phage type 1 at the age of 7 days (experiment A: lines 1 and 2) and at the age of 1 day (experiment B: lines 3 and 4). At various days post-infection chickens were sacrificed and the number of Salmonella in the caeca, liver, and spleen were determined. Furthermore, phagocytic activity, cellular immune responses, and humoral responses were determined using, respectively, single-cell suspensions of spleen or intestine and serum. In both experiments, similar trends were seen. Increased numbers of S. enteritidis were found in the caeca of lines 1 and 3, whereas at the same time a decreased colonization was found in the spleen and in the liver, as compared to lines 2 and 4. In the latter two lines, the phagocytic activity of the phagocytes was higher and the humoral responses were lower. Observations from this study suggest that lower activity of phagocytes and higher humoral activity prevent systemic S. enteritidis infection.

Protective effect of Enterococcus faecium J96, a potential probiotic strain, on chicks infected with Salmonella Pullorum

Enterococcus faecium J96 was isolated from a healthy free-range chicken and it inhibited Salmonella Pullorum, in vitro, due to its lactic acid and bacteriocin production. In vivo assays were carried out with 30-h-old broiler chicks. The lactic acid bacteria (approximately 1 x 10(9) cells per chick) were orally administered as preventive and as therapeutic treatments. In the first case they were given to the chicks twice a day for 3 consecutive days. In the second case the lactic bacteria were administered in the same way after a 24-h challenge by Salmonella Pullorum (in both instances the salmonella dose was 1 x 10(5) cells per chick). Cecal contents, liver, and spleens were analyzed and liver and spleen fragments were also fixed in formaldehyde (pH 7.00) in order to determine salmonella translocation. The chickens that were preventively treated with E. faecium J96 survived the Salmonella Pullorum challenge. Those that were infected on the first day and then inoculated with lactic bacteria died 4 days later. Salmonellae were isolated from their livers and spleens. From these results we may conclude that E. faecium J96 can protect newly hatched chicks from Salmonella Pullorum infection but cannot act as a good therapeutic agent.

Estimating the annual fraction of eggs contaminated with Salmonella enteritidis in the United States

Using available data on the occurrence of Salmonella enteritidis (SE) in US layer flocks and eggs, and a probabilistic scenario tree method, an estimate of the fraction of SE-contaminated eggs produced annually is derived with attendant uncertainty. In lieu of a definitive prevalence survey, the approach presented here provides insight to the relative contribution of various pathways leading to contaminated eggs. A Monte Carlo model with four branches is developed. The first branch predicts the proportion of all US flocks that are SE-affected. The second branch apportions SE-affected flocks into three categories (high, moderate, and low level affected flocks) based on population-adjusted epidemiologic data. The third branch predicts the proportion of affected flocks that are molted and producing eggs during a high risk period subsequent to molt. The fourth branch predicts the fraction of contaminated eggs produced by flocks of the type described by the pathway (e.g. high level affected flocks that are not molted) based on egg sampling evidence from naturally infected flocks. The model is simulated to account for uncertainty in the data used to estimate the branch probabilities. Correlation analysis is used to estimate the sensitivity of model output to various model inputs. The output of this model is an uncertainty distribution for the fraction of all eggs that are SE-contaminated during 1 year of production in the US. The expected value of this distribution is approximately one SE-affected egg in every 20,000 eggs annually produced, and the 90% certainty interval is between one SE-contaminated egg in 30,000 eggs, and one SE-contaminated egg in 12,000 eggs. The model estimates that an average of 14% of all eggs (i.e. contaminated and not contaminated) from affected flocks are produced by high level, non-molted affected flocks, but these flocks are estimated to account for more than two-thirds of the total fraction of contaminated eggs produced annually. Sensitivity analysis also suggests that the proportion of affected flocks that are high level flocks - and the egg contamination frequency for these types of flocks - are the most sensitive model inputs. The model's pathways provide a framework for evaluating interventions to reduce the number of contaminated eggs produced in the US. Furthermore, sensitivity analysis of the model identifies those inputs whose uncertainty is most influential on the model's output. Future farm-level research priorities can be established on the basis of this analysis, but public policy decisions require a fuller exposure assessment and dose-response analysis to account for microbial growth dynamics, meal preparation, and consumption demographics among US egg consumers.

In vitro attachment and invasion of chicken ovarian granulosa cells by Salmonella enteritidis phage type 8

The attachment and invasion of chicken ovarian granulosa cells by Salmonella enteritidis was examined in vitro. The attachment was inhibited by preincubation of granulosa cells with anti-chicken fibronectin antibody (approximately 70% reduction in attachment) or preincubation with a 14-kDa fimbrial protein isolated from S. enteritidis (68% reduction in attachment). Treatment of bacterial cells with the tetrapeptide RGDS before addition to granulosa cells resulted in inhibition of attachment (60% inhibition when 2 x 10(7) CFU of bacteria was treated with 500 microg of peptide). Treatment with the peptide GRGD resulted in similar magnitude of inhibition, indicating that extracellular matrix proteins play significant roles in the interaction of S. enteritidis with granulosa cells. In contrast, treatment of the bacterial cells with the peptide GRAD did not result in significant inhibition of attachment to the granulosa cells. S. enteritidis was found to attach specifically to fibronectin, collagen IV, and laminin-coated microtiter plate wells, with the rank order of attachment as follows: fibronectin > laminin > collagen IV. Light and transmission electron micrographs of S. enteritidis invasion of granulosa cells showed organisms with or without a surrounding membrane in the cytoplasm of granulosa cells. In some instances, dividing bacterial cells were observed in the cytoplasm. Results of this study demonstrated that S. enteritidis interacts with granulosa cells in a specific manner and can invade and multiply in these cells. The granulosa cell layer of the preovulatory follicles may be a preferred site for the colonization of the chicken ovaries by invasive strains of S. enteritidis.

Experimental infection of laying hens with Salmonella enteritidis strains that express different types of fimbriae

A study was conducted to compare the pathogenicity of three Salmonella enteritidis phage type 8 strains (9, 21, and 30) in 30-wk-old laying hens. Strain 9 expressed two types of fimbriae of 14 and 21 kDa. Strain 30 expressed a single fimbrial type (21 kDa). Strain 21 did not express any fimbrial protein. Laying hens were divided into three groups of 35 each and each group was orally inoculated with a single S. enteritidis strain (1 x 10(8) cfu per bird). Significantly less intensive cecal colonization and fecal shedding of the organism were observed in hens that were inoculated with the strain that did not express fimbriae than in birds inoculated with other two strains (P < 0.05). Isolation of S. enteritidis from liver, spleen, reproductive organs, and egg contents did not differ between groups. Mean serum S. enteritidis lipopolysaccharide-specific antibody titers of birds inoculated with strain 21 were lower than titers of hens that were inoculated with the other two strains from the 5th wk through the end of the trial. Immunoblot of the bacterial outer membrane structures revealed the presence of serum antibodies against lipopolysaccharide, membrane-associated proteins, and purified 14 kDa fimbrial protein in birds inoculated with strain 9 as late as 9 wk postinoculation. Results of this study are consistent with a role for fimbrial proteins in the cecal colonization by S. enteritidis. In addition, cecal colonization mediated by fimbrial proteins may enhance the elicitation of humoral immune response against S. enteritidis.

Line differences in resistance to Salmonella enteritidis PT4 infection

1. Four groups of hens, each of a different line, were inoculated at peak of lay, per os in the crop with 1 ml of a suspension containing 10(9) cfu/ml Salmonella enteritidis PT4 (SE). The kinetics of SE contamination in the environment, egg shell and yolk were studied during the first 28 d post inoculation. On the day of slaughter, intestines, caeca, spleen, liver, ovary, oviduct and content were investigated for SE contamination. 2. The commercial egg-type line L2 was found to be the most susceptible to SE. It laid many SE-positive yolks (13.8%) and internal and faecal organs were frequently infected. 3. Certain lines are found to exhibit a degree of resistance to SE; the cause of which is unknown and might be attributed to major genes.

Salmonella enteritidis colonization of the reproductive tract and forming and freshly laid eggs of chickens

Salmonella enteritidis colonizes the tissues of the chicken ovary and oviduct, presumably contaminating eggs and thereby contributing to human outbreaks of salmonellosis. In this study, commercial adult laying hens were given an oral inoculation of 10(8) S. enteritidis organisms. Tissues from various organs, the intestines, and the reproductive tract, including freshly laid eggs, were collected daily for up to 40 days postinoculation (p.i.). Within 2 days p.i. S. enteritidis was detected by culture in pools of the spleen, liver, heart, and gallbladder tissues, in intestinal tissues of all infected birds, and in various sections of the ovary and oviduct. Detection of organisms by immunohistochemical staining was rare for most tissues in spite of their culture-positive status, suggesting a low level of tissue colonization. However, S. enteritidis could be detected by immunohistochemical staining in oviduct tissues associated with four forming eggs, indicating the possibility of a heavier colonization in the egg during its development. In two subsequent experiments, forming eggs taken from the oviduct with their associated tissue, were found to be culture positive for S. enteritidis at a rate of 27.1 and 31.4%, while freshly laid eggs in these experiments were culture positive at the rate of 0 and 0.6%. These observations suggest that while forming eggs are significantly colonized in the reproductive tract, factors within the eggs may control the pathogen before the eggs are laid. The data show that prior to egg deposition, forming eggs are subject to descending infections from colonized ovarian tissue, ascending infections from colonized vaginal and cloacal tissues, and lateral infections from colonized upper oviduct tissues. The data are consistent with an ascending infection of freshly laid eggs from the cloaca, as the incidence of positive eggs in experiments 1 and 3 coincided with heavily contaminated cloacal tissues (50.7 and 80%, respectively), while no positive eggs were detected in experiment 2 when cloacal colonization was low (8.3%). The data do not support the possibility of egg invasion by bacterial translocation from the peritoneal cavity.