Effect of type 1 fimbriae of Salmonella enterica serotype Enteritidis on bacteraemia and reproductive tract infection in laying hens

Integrated OMICs approach reveals energy metabolism pathway is vital for Salmonella Pullorum survival within the egg white

Eggs, an important part of a healthy daily diet, can protect chicken embryo development due to the shell barrier and various antibacterial components within the egg white. Our previous study demonstrated that Salmonella Pullorum, highly adapted to chickens, can survive in the egg white and, therefore, be passed to newly hatched chicks. However, the survival strategy of Salmonella Pullorum in antibacterial conditions remains unknown. The overall transcripts in the egg white showed a large-scale shift compared to LB broth. The expression of common response genes and pathways, such as those involved in iron uptake, biotin biosynthesis, and virulence, was significantly changed, consistent with the other transovarial transmission serovar Enteritidis. Notably, membrane stress response, amino acid metabolism, and carbohydrate metabolism were specifically affected. Additional upregulated functionally relevant genes (JI728_13095, JI728_13100, JI728_17960, JI728_10085, JI728_15605, and nhaA) as mutants confirmed the susceptible phenotype. Furthermore, fim deletion resulted in an increased survival capacity in the egg white, consistent with the downregulated expression. The second-round RNA-Seq analysis of the Δfim mutant in the egg white revealed significantly upregulated genes compared with the wild type in the egg white responsible for energy metabolism located on the hyc and hyp operons regulated by FhlA, indicating the Δfim mutant cannot receive enough oxygen and switched to fermentative growth due to its inability to attach to the albumen surface. Together, this study provides a first estimate of the global transcriptional response of Salmonella Pullorum under antibacterial egg white and highlights the new potential role of fim deletion in optimizing energy metabolism pathways that may assist vertical transmission.

IMPORTANCE

Pullorum disease, causing serious embryo death and chick mortality, results in substantial economic losses worldwide due to transovarial transmission. Egg-borne outbreaks are frequently reported in many countries. The present study has filled the knowledge gap regarding how the specific chicken-adapted pathogen Salmonella Pullorum behaves within the challenging environment of egg white. The deletion of the fim fimbrial system can increase survival in the albumen, possibly by reprogramming metabolism-related gene products, which reveals a new adaptive strategy of pathogens. Moreover, the comparison, including previous research on Salmonella Enteritidis, capable of vertical transmission, aims to provide diversified data sets in the field and further help to implement reasonable and effective measures to improve both food safety and animal health.

Unraveling the role of type 1 fimbriae in Salmonella pathogenesis: insights from a comparative analysis of Salmonella Enteritidis and Salmonella Gallinarum

Significant differences in pathogenicity between Salmonella Enteritidis and Salmonella Gallinarum exist despite the fact that S. Gallinarum is a direct descendant of S. Enteritidis. It was hypothesized that such various properties may be in part the result of differences in structure and functions of type 1 fimbriae (T1Fs). In S. Enteritidis, T1Fs bind to oligomannosidic structures carried by host cell glycoproteins and are called mannose-sensitive T1Fs (MST1F). In S. Gallinarum, T1Fs lost ability to bind such carbohydrate chains, and were named mannose-resistant MRT1Fs (MRT1F). Therefore, the present study was undertaken to evaluate the role of MST1Fs and MRT1Fs in the adhesion, invasion, intracellular survival and cytotoxicity of S. Enteritidis and S. Gallinarum toward chicken intestinal CHIC8-E11cells and macrophage-like HD11 cells. Using mutant strains: S. Enteritidis fimH::kan and S. Gallinarum fimH::kan devoid of T1Fs and in vitro assays the following observations were made. MST1Fs have a significant impact on the chicken cell invasion by S. Enteritidis as MST1F-mediated adhesion facilitates direct and stable contact of bacteria with host cells, in contrast to MRT1Fs expressed by S. Gallinarum. MST1Fs as well as MRT1Fs did not affected intracellular viability of S. Enteritidis and S. Gallinarum. However, absolute numbers of intracellular viable wild-type S. Enteritidis were significantly higher than S. Enteritidis fimH::kan mutant and wild-type S. Gallinarum and S. Gallinarum fimH::kan mutant. These differences, reflecting the numbers of adherent and invading bacteria, underline the importance of MST1Fs in the pathogenicity of S. Enteritidis infections. The cytotoxicity of wild-type S. Enteritidis and its mutant devoid of MST1Fs to HD11 cells was essentially the same, despite the fact that the number of viable intracellular bacteria was significantly lower in the mutated strain. Using HD11 cells with similar number of intracellular wild-type S. Enteritidis and S. Enteritidis fimH::kan mutant, it was found that the lack of MST1Fs did not affect directly the cytotoxicity, suggesting that the increase in cytotoxicity of S. Enteritidis devoid of MST1Fs may be associated with crosstalk between T1Fs and other virulence factors.

Benefits and risks of using bacterial- and plant-produced nano-silver for Japanese quail hatching-egg sanitation

This research compared how bacterial-, plant-produced silver nanoparticles (Ag-NPs) and TH4 affected the eggshells microbial load and quail chicks' liver structure, embryonic mortality, and features related to hatchability. Ag-NPs were sensitized by bacterial and plant methods, and then identified by UV-visible spectroscopy, TEM, and FTIR spectroscopy. B-Ag-NPs were found in spherical shapes in size ranging from 7.09 to 18.1 nm versus multi-shape with size range of 25.0-78.1 nm for P-Ag-NPs. A total number of 624 eggs (in three equal groups) of Japanese quail flock were sprayed with TH4 as control, B-Ag-NPs and P-Ag-NPs. Thereafter, three eggs were sampled randomly from each group for determining important microbial groups. The remaining eggs were incubated according to the recommended incubation conditions. On the day of hatching, the percentages of hatchability and embryonic mortality were measured. Besides, five chicks from each treatment were slaughtered and the livers were utilized for ICP and histological tests. The effects of all three treatments on the microbial count in eggshells were comparable, according to the results. In addition, there was no negative effect on either hatchability percentage or embryonic mortality rate. The liver structure from both B-Ag-NPs and P-Ag-NPs treatments exhibited severe and moderate degeneration of hepatocytes, which may indicate possible hazardous effects of using nanoparticles. Using TH4 did not cause liver structure abnormality. In conclusion, using Ag-NPs for sanitizing hatching eggs effectively reduces the eggshell microbial count without affecting the hatchability percentage. Nevertheless, histological changes are appropriate to be considered as a safety parameter in Ag-NPs applications.

The Role of Egg Yolk in Modulating the Virulence of Salmonella Enterica Serovar Enteritidis

Contribution of food vehicles to pathogenicity of disease-causing microorganisms is an important but overlooked research field. The current study was initiated to reveal the relationship between virulence of Salmonella enterica serovar Enteritidis and egg yolk as a hosting medium. Mice were orally challenged with Salmonella Enteritidis cultured in egg yolk or tryptic soy broth (TSB). Additionally, mice were challenged with Salmonella Enteritidis cultured in TSB, followed by administration of sterile egg yolk, to discern the difference between pre-growth of the pathogen and its mere presence in egg yolk during infection. The pathogen's Lethal dose 50 (LD50) was the lowest when grown in yolk (2.8×102 CFU), compared to 1.1×103 CFU in TSB, and 4.6×103 CFU in TSB followed by administration of sterile yolk. Additionally, mice that orally received Salmonella Enteritidis grown in egg yolk expressed a high death rate. These findings were supported by transcriptional analysis results. Expression of promoters of virulence-related genes (sopB and sseA) in genetically modified Salmonella Enteritidis reporter strains was significantly higher (p < 0.05) when the bacterium was grown in the yolk, compared to that grown in TSB. Sequencing of RNA (RNA-seq) revealed 204 differentially transcribed genes in Salmonella Enteritidis grown in yolk vs. TSB. Yolk-grown Salmonella Enteritidis exhibited upregulated virulence pathways, including type III secretion systems, epithelial cell invasion, and infection processes; these observations were confirmed by RT-qPCR results. The transcriptomic analysis suggested that upregulation of virulence machinery of Salmonella Enteritidis grown in egg yolk was related to increased iron uptake, biotin utilization, flagellar biosynthesis, and export of virulence proteins encoded on Salmonella pathogenicity island 1, 2, 4, and 5. These biological responses may have acted in concert to increase the virulence of Salmonella infection in mice. In conclusion, growth in egg yolk enhanced Salmonella Enteritidis virulence, indicating the significance of this food vehicle to the risk assessment of salmonellosis.

Sodium Butyrate Reduces Salmonella Enteritidis Infection of Chicken Enterocytes and Expression of Inflammatory Host Genes in vitro

Salmonella Enteritidis (SE) is a facultative intracellular pathogen that colonizes the chicken gut leading to contamination of carcasses during processing. A reduction in intestinal colonization by SE could result in reduced carcass contamination thereby reducing the risk of illnesses in humans. Short chain fatty acids such as butyrate are microbial metabolites produced in the gut that exert various beneficial effects. However, its effect on SE colonization is not well known. The present study investigated the effect of sub-inhibitory concentrations (SICs) of sodium butyrate on the adhesion and invasion of SE in primary chicken enterocytes and chicken macrophages. In addition, the effect of sodium butyrate on the expression of SE virulence genes and selected inflammatory genes in chicken macrophages challenged with SE were investigated. Based on the growth curve analysis, the two SICs of sodium butyrate that did not reduce SE growth were 22 and 45 mM, respectively. The SICs of sodium butyrate did not affect the viability and proliferation of chicken enterocytes and macrophage cells. The SICs of sodium butyrate reduced SE adhesion by ∼1.7 and 1.8 Log CFU/mL, respectively. The SE invasion was reduced by ∼2 and 2.93 Log CFU/mL, respectively in chicken enterocytes (P < 0.05). Sodium butyrate did not significantly affect the adhesion of SE to chicken macrophages. However, 45 mM sodium butyrate reduced invasion by ∼1.7 Log CFU/mL as compared to control (P < 0.05). Exposure to sodium butyrate did not change the expression of SE genes associated with motility (flgG, prot6E), invasion (invH), type 3 secretion system (sipB, pipB), survival in macrophages (spvB, mgtC), cell wall and membrane integrity (tatA), efflux pump regulator (mrr1) and global virulence regulation (lrp) (P > 0.05). However, a few genes contributing to type-3 secretion system (ssaV, sipA), adherence (sopB), macrophage survival (sodC) and oxidative stress (rpoS) were upregulated by at least twofold. The expression of inflammatory genes (Il1β, Il8, and Mmp9) that are triggered by SE for host colonization was significantly downregulated (at least 25-fold) by sodium butyrate as compared to SE (P < 0.05). The results suggest that sodium butyrate has an anti-inflammatory potential to reduce SE colonization in chickens.

Small non-coding RNA STnc640 regulates expression of fimA fimbrial gene and virulence of Salmonella enterica serovar Enteritidis

Background

Small non-coding RNAs (sRNAs) regulate bacterial gene expression at the post-transcriptional level. STnc640 is a type of sRNA that was identified in Salmonella Typhimurium.

Results

In this study, STnc640 in Salmonella Enteritidis was confirmed to be an Hfq-dependent sRNA. TargetRNA software analysis showed that fimbrial genes fimA and bcfA were likely to be the target genes of STnc640. To investigate the target mRNAs and function of STnc640 in pathogenicity, we constructed the deletion mutant strain 50336△stnc640 and the complemented strain 50336△stnc640/pstnc640 in Salmonella Enteritidis 50336. The RT-qPCR results showed that the mRNA level of fimA was decreased, while bcfA was unchanged in 50336△stnc640 compared with that in the wild type (WT) strain. The adhesion ability of 50336△stnc640 to Caco-2 cells was increased compared to the 50336 WT strain. The virulence of 50336△stnc640 was enhanced in a one-day-old chicken model of S. Enteritidis disease as determined by quantifying the 50% lethal dose (LD₅₀) of the bacterial strains.

Conclusions

The results demonstrate that STnc640 contributes to the virulence of Salmonella Enteritidis.

Everything You Always Wanted to Know About Salmonella Type 1 Fimbriae, but Were Afraid to Ask

Initial attachment to host intestinal mucosa after oral infection is one of the most important stages during bacterial pathogenesis. Adhesive structures, widely present on the bacterial surface, are mainly responsible for the first contact with host cells and of host-pathogen interactions. Among dozens of different bacterial adhesins, type 1 fimbriae (T1F) are one of the most common adhesive organelles in the members of the Enterobacteriaceae family, including Salmonella spp., and are important virulence factors. Those long, thin structures, composed mainly of FimA proteins, are responsible for recognizing and binding high-mannose oligosaccharides, which are carried by various glycoproteins and expressed at the host cell surface, via FimH adhesin, which is presented at the top of T1F. In this review, we discuss investigations into the functions of T1F, from the earliest work published in 1958 to operon organization, organelle structure, T1F biogenesis, and the various functions of T1F in Salmonella-host interactions. We give special attention to regulation of T1F expression and their role in binding of Salmonella to cells, cell lines, organ explants, and other surfaces with emphasis on biofilm formation and discuss T1F role as virulence factors based on work using animal models. We also discuss the importance of allelic variation in fimH to Salmonella pathogenesis, as well as role of FimH in Salmonella host specificity.

Salmonella control in poultry flocks and its public health impact

An increase in confirmed human salmonellosis cases in the EU after 2014 triggered investigation of contributory factors and control options in poultry production. Reconsideration of the five current target serovars for breeding hens showed that there is justification for retaining Salmonella Enteritidis, Salmonella Typhimurium (including monophasic variants) and Salmonella Infantis, while Salmonella Virchow and Salmonella Hadar could be replaced by Salmonella Kentucky and either Salmonella Heidelberg, Salmonella Thompson or a variable serovar in national prevalence targets. However, a target that incorporates all serovars is expected to be more effective as the most relevant serovars in breeding flocks vary between Member State (MS) and over time. Achievement of a 1% target for the current target serovars in laying hen flocks is estimated to be reduced by 254,400 CrI95[98,540; 602,700] compared to the situation in 2016. This translates to a reduction of 53.4% CrI95[39.1; 65.7] considering the layer-associated human salmonellosis true cases and 6.2% considering the overall human salmonellosis true cases in the 23 MSs included in attribution modelling. A review of risk factors for Salmonella in laying hens revealed that overall evidence points to a lower occurrence in non-cage compared to cage systems. A conclusion on the effect of outdoor access or impact of the shift from conventional to enriched cages could not be reached. A similar review for broiler chickens concluded that the evidence that outdoor access affects the occurrence of Salmonella is inconclusive. There is conclusive evidence that an increased stocking density, larger farms and stress result in increased occurrence, persistence and spread of Salmonella in laying hen flocks. Based on scientific evidence, an impact of Salmonella control programmes, apart from general hygiene procedures, on the prevalence of Campylobacter in broiler flocks at the holding and on broiler meat at the end of the slaughter process is not expected.

Distribution of Salmonella Enteritidis in internal organs and variation of cecum microbiota in chicken after oral challenge

The aim study was to explore the distribution of Salmonella Enteritidis (S. enteritidis) in internal organs and variation of cecum microbiota in newly hatched chicken after oral challenge during a 21-day period. The quantities of S. enteritidis DNA in different internal organs (heart, liver, spleen, stomach, pancreas, small intestine, blood and cecum contents) were determined by real-time fluorescent quantitative polymerase chain reaction (FQ-PCR). The result showed that all of the above-mentioned samples were positive at 12 h post inoculation (PI) after oral challenge. The highest copy numbers of S. enteritidis in all tissue were heart and liver, with about 2 × 10² to 6 × 10⁶ copies of DNA target sequences/0.5 g. The copy number of S. enteritidis in the stomach was only lower than the heart and liver. The blood at 8 d PI, the pancreas at 10 d PI, the heart at 14 d PI and the stomach at 17 d PI didn't have a positive result. However, the liver, spleen, cecum contents and small intestine were all positive during the 21-day period. The cecum contents at 0 d PI, 4 d PI and 10 d PI from the control group and experiment group were collected for bacterial 16 S rRNA sequencing targeting the V3-V4 hypervariable region. The result showed that at the 0 d PI, the main cecum microbiota ingredient of the two-day old chicken was Enterobacteriaceae (Proteobacteria) and the other microbiology species were fewer. At the 10 d PI, the microbiota ingredient of cecum became abundant and stable mainly including the families Ruminococcaceae (Firmicutes), Enterobacteriaceae (Proteobacteria), Lachnospiraceae (Firmicutes) and clostridiacaea (Firmicutes) both of the two group, suggesting Salmonella infection with 2-day old chicken might not significantly change cecum microbiota community. The study indicated the major organs, which carried numerous S. enteritidis, providing a significantly guideline for salmonella detection in poultry and revealed the main microbiota ingredient of chicken cecum.

Pili Assembled by the Chaperone/Usher Pathway in Escherichia coli and Salmonella

Gram-negative bacteria assemble a variety of surface structures, including the hair-like organelles known as pili or fimbriae. Pili typically function in adhesion and mediate interactions with various surfaces, with other bacteria, and with other types of cells such as host cells. The chaperone/usher (CU) pathway assembles a widespread class of adhesive and virulence-associated pili. Pilus biogenesis by the CU pathway requires a dedicated periplasmic chaperone and integral outer membrane protein termed the usher, which forms a multifunctional assembly and secretion platform. This review addresses the molecular and biochemical aspects of the CU pathway in detail, focusing on the type 1 and P pili expressed by uropathogenic Escherichia coli as model systems. We provide an overview of representative CU pili expressed by E. coli and Salmonella, and conclude with a discussion of potential approaches to develop antivirulence therapeutics that interfere with pilus assembly or function.

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.

Prevention of egg contamination by Salmonella Enteritidis after oral vaccination of laying hens with Salmonella Enteritidis ΔtolC and ΔacrABacrEFmdtABC mutants

Vaccination of laying hens has been successfully used to reduce egg contamination by Salmonella Enteritidis, decreasing human salmonellosis cases worldwide. Currently used vaccines for layers are either inactivated vaccines or live attenuated strains produced by mutagenesis. Targeted gene deletion mutants hold promise for future vaccines, because specific bacterial functions can be removed that may improve safety and allow differentiation from field strains. In this study, the efficacy of Salmonella Enteritidis ΔtolC and ΔacrABacrEFmdtABC strains in laying hens as live vaccines was evaluated. The mutants are deficient in either the membrane channel TolC (ΔtolC) or the multi-drug efflux systems acrAB, acrEF and mdtABC (ΔacrABacrEFmdtABC). These strains have a decreased ability for gut and tissue colonization and are unable to survive in egg white, the latter preventing transmission of the vaccine strains to humans. Two groups of 30 laying hens were orally inoculated at day 1, 6 weeks and 16 weeks of age with 10⁸ cfu of either vaccine strain, while a third group was left unvaccinated. At 24 weeks of age, the birds were intravenously challenged with 5 × 10⁷ cfu Salmonella Enteritidis PT4 S1400/94. The vaccine strains were not shed or detected in the gut, internal organs or eggs, 2 weeks after the third vaccination. The strains significantly protected against gut and internal organ colonization, and completely prevented egg contamination by Salmonella Enteritidis under the conditions of this study. This indicates that Salmonella Enteritidis ΔtolC and ΔacrABacrEFmdtABC strains might be valuable strains for vaccination of layers against Salmonella Enteritidis.

Type 1 fimbriae are important factors limiting the dissemination and colonization of mice by Salmonella Enteritidis and contribute to the induction of intestinal inflammation during Salmonella invasion

We have recently shown that Salmonella Gallinarum type 1 fimbriae with endogenous mannose-resistant (MR) variant of the FimH protein increase systemic dissemination of S. Gallinarum and colonization of internal organs in comparison to the S. Gallinarum fimH knockout strain or the mutant expressing mannose-sensitive (MS) FimH variant from S. Enteritidis. Elaborating from these studies, we proposed that MS variants of FimH are advantageous in gastrointestinal infections, in contrast to MR FimH variants which decrease intestinal colonization and promote their systemic spreading. To support our hypothesis, we carried out in vivo studies using mice infected with wild-type S. Enteritidis and its fimH knockout strain (S. Enteritidis), which was characterized by significantly lower adhesion and invasiveness of murine ICE-1 intestinal cells. Using bioluminescence imaging, we observed that the loss of MS FimH adhesin correlates well with the highly increased colonization of mice by these bacteria. The appearance of the mutant strain was observed much earlier than wild-type Salmonella, and mice infected with 10⁴–10⁷S. Enteritidis fimH::kan CFUs had significantly (P < 0.05) shorter infection-free time than animals inoculated with wild-type S. Enteritidis. Infections caused by non-typhoid Salmonella, such as S. Enteritidis, are associated with massive inflammation of the lamina propria and lymph nodes in the intestinal tract. Therefore, we evaluated the role of MS type 1 fimbriae in the induction of cytokine expression and secretion, using murine ICE-1 intestinal cells. We showed that the expression, as well as secretion, of Il-1b, Il-6, Il-10, and Il-12b was significantly higher in cells infected with wild-type S. Enteritidis compared to cells infected with the mutant strain. Based on our results, we propose that type 1 fimbriae may play an important role in the pathogenicity of S. Enteritidis and may contribute to an intestinal inflammatory response.

In-feed supplementation of trans-cinnamaldehyde reduces layer-chicken egg-borne transmission of Salmonella enterica serovar enteritidis

Salmonella enterica serovar Enteritidis is a major foodborne pathogen in the United States, causing gastroenteritis in humans, primarily through consumption of contaminated eggs. Chickens are the reservoir host of S. Enteritidis. In layer hens, S. Enteritidis colonizes the intestine and migrates to various organs, including the oviduct, leading to egg contamination. This study investigated the efficacy of in-feed supplementation with trans-cinnamaldehyde (TC), a generally recognized as safe (GRAS) plant compound obtained from cinnamon, in reducing S. Enteritidis cecal colonization and systemic spread in layers. Additionally, the effect of TC on S. Enteritidis virulence factors critical for macrophage survival and oviduct colonization was investigated in vitro. The consumer acceptability of eggs was also determined by a triangle test. Supplementation of TC in feed for 66 days at 1 or 1.5% (vol/wt) for 40- or 25-week-old layer chickens decreased the amounts of S. Enteritidis on eggshell and in yolk (P<0.001). Additionally, S. Enteritidis persistence in the cecum, liver, and oviduct in TC-supplemented birds was decreased compared to that in controls (P<0.001). No significant differences in feed intake, body weight, or egg production in birds or in consumer acceptability of eggs were observed (P>0.05). In vitro cell culture assays revealed that TC reduced S. Enteritidis adhesion to and invasion of primary chicken oviduct epithelial cells and reduced S. Enteritidis survival in chicken macrophages (P<0.001). Follow-up gene expression analysis using real-time quantitative PCR (qPCR) showed that TC downregulated the expression of S. Enteritidis virulence genes critical for chicken oviduct colonization (P<0.001). The results suggest that TC may potentially be used as a feed additive to reduce egg-borne transmission of S. Enteritidis.

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.

The RNA chaperone Hfq regulates expression of fimbrial-related genes and virulence of Salmonella enterica serovar Enteritidis

Salmonella Enteritidis is an intracellular pathogen that causes enteritis and systemic disease in humans and other animals. The RNA chaperone protein Hfq mediates the binding of small noncoding RNAs to target mRNA and assists in post-transcriptional gene regulation in bacteria. In this study, we constructed an hfq deletion mutant in S. Enteritidis SE50336 and analyzed the expression of major fimbrial subunits sefA, bcfA, fimA, safA, stbA, sthA, csgA, csgD, and pegA using quantitative real-time PCR. The gene expression of sefA increased about 14-fold in the hfq mutant, as compared with its expression in the wild-type strain. The expression of fimA and pegA did not change significantly, while the expression of the other fimbrial genes was significantly down-regulated in the hfq mutant. The ability of SE50336Δhfq adhering to Caco-2 cells was also reduced as compared with wild-type adherence. The virulence of the hfq mutant was significantly reduced in a 1-day-old chicken model of S. Enteritidis disease, as determined by quantifying the lethal dose 50% of the bacterial strains. We conclude that Hfq critically contributes to S. Enteritidis virulence, likely partially affected by regulating fimbrial gene expression.

Effect of plant derived antimicrobials on Salmonella enteritidis adhesion to and invasion of primary chicken oviduct epithelial cells in vitro and virulence gene expression

Salmonella Enteritidis (SE) is a major foodborne pathogen in the United States and one of the most frequently reported Salmonella serotypes globally. Eggs are the most common food product associated with SE infections in humans. The pathogen colonizes the intestinal tract in layers, and migrates to reproductive organs systemically. Since adhesion to and invasion of chicken oviduct epithelial cells (COEC) is critical for SE colonization in reproductive tract, reducing these virulence factors could potentially decrease egg yolk contamination. This study investigated the efficacy of sub-inhibitory concentrations of three plant-derived antimicrobials (PDAs), namely carvacrol, thymol and eugenol in reducing SE adhesion to and invasion of COEC, and survival in chicken macrophages. In addition, the effect of PDAs on SE genes critical for oviduct colonization and macrophage survival was determined using real-time quantitative PCR (RT-qPCR). All PDAs significantly reduced SE adhesion to and invasion of COEC (p < 0.001). The PDAs, except thymol consistently decreased SE survival in macrophages (p < 0.001). RT-qPCR results revealed down-regulation in the expression of genes involved in SE colonization and macrophage survival (p < 0.001). The results indicate that PDAs could potentially be used to control SE colonization in chicken reproductive tract; however, in vivo studies validating these results are warranted.

Single nucleotide polypmorphisms of fimH associated with adherence and biofilm formation by serovars of Salmonella enterica

Type 1 fimbriae produced by serovars of Salmonella are characterized by their ability to agglutinate guinea pig erythrocytes in the absence of d-mannose but not in its presence. The FimH protein is the adhesin that mediates this reaction; it is distinct from the major fimbrial protei.n (FimA) that composes the fimbrial shaft. Avian-adapted serovars of Salmonella produce non-haemagglutinating fimbriae that have been reported to mediate adherence to avian cells. A single amino acid substitution is present in the FimH adhesin of these strains compared to that of a Typhimurium isolate. Also, previous studies have shown that single nucleotide polymorphisms in two strains of the Typhimurium fimH alter the binding specificity. We therefore investigated the allelic variation of fimH from a range of serotypes (both host-adapted and non-host-adapted) and isolates of Salmonella. Most FimH adhesins mediated the mannose-sensitive haemagglutination of guinea pig erythrocytes, but many did not facilitate adherence to HEp-2 cells. A small number of isolates also produced fimbriae but did not mediate adherence to either cell type. Transformants possessing cloned fimH genes exhibited a number of different substitutions within the predicted amino acid sequence of the FimH polypeptide. No identical FimH amino sequence was found between strains that adhere to erythrocytes and/or HEp-2 cells and those produced by non-adherent strains. FimH-mediated adherence to HEp-2 cells was invariably associated with the ability to form biofilms on mannosylated bovine serum albumin.

Efficacy of several vaccination programmes in commercial layer and broiler breeder hens against experimental challenge with Salmonella enterica serovar Enteritidis

Two experiments were performed to evaluate the protective effect of various vaccination combinations given at 5 and 9 weeks of age against experimental challenge with Salmonella enterica serovar Enteritidis (SE) phage type 4 at 12 weeks of age. In Experiment 1, groups of commercial layers were vaccinated by one of the following programmes: Group 1, two doses of a SE bacterin (Layermune SE); Group 2, one dose of a live Salmonella enterica serovar Gallinarum vaccine (Cevac SG9R) followed by one dose of the SE bacterin; Group 3, one dose of each of two different multivalent inactivated vaccines containing SE cells (Corymune 4K and Corymune 7K; and Group 4, unvaccinated, challenged controls. In Experiment 2, groups of broiler breeders were vaccinated by the same programmes as Groups 1 and 2 above while Group 3 was an unvaccinated, challenged control group. All vaccination programmes and the challenge induced significant (P < 0.05) seroconversion as measured by enzyme-linked immunosorbent assay. Overall, in both experiments, all vaccination schemes were significantly effective in reducing organ (spleen, liver and caeca) colonization by the challenge strain as well as reducing faecal excretion for at least 3 weeks. Vaccinated layers in Groups 1 and 2 and broiler breeders in Group 2 showed the greatest reduction in organ colonization and the least faecal excretion. In Experiment 1, layers vaccinated with multivalent inactivated vaccines containing a SE component (Group 3) were only moderately protected, indicating that such a vaccination programme may be useful in farms with good husbandry and housing conditions and low environmental infectious pressure by Salmonella.

Quantitative analysis of Salmonella Enteritidis loads in ducklings after nasal inoculation

The distribution patterns of Salmonella Enteritidis in systemic organs, which have not been described previously, should be studied to better understand its pathogenesis in vivo. We inoculated the ducklings with Salmonella Enteritidis via the nasal route and performed a real-time PCR assay for determining the concentration of Salmonella Enteritidis DNA and studied the histopathology of various tissues postinoculation. The results show that the Salmonella Enteritidis load in systemic organs has a close correlation with the progression of disease. Further, rapid dissemination and active replication of Salmonella Enteritidis in multiple systemic organs accelerated the progression of disease.

Molecular insights into farm animal and zoonotic Salmonella infections

Salmonella enterica is a facultative intracellular pathogen of worldwide importance. Infections may present in a variety of ways, from asymptomatic colonization to inflammatory diarrhoea or typhoid fever depending on serovar- and host-specific factors. Human diarrhoeal infections are frequently acquired via the food chain and farm environment by virtue of the ability of selected non-typhoidal serovars to colonize the intestines of food-producing animals and contaminate the avian reproductive tract and egg. Colonization of reservoir hosts often occurs in the absence of clinical symptoms; however, some S. enterica serovars threaten animal health owing to their ability to cause acute enteritis or translocate from the intestines to other organs causing fever, septicaemia and abortion. Despite the availability of complete genome sequences of isolates representing several serovars, the molecular mechanisms underlying Salmonella colonization, pathogenesis and transmission in reservoir hosts remain ill-defined. Here we review current knowledge of the bacterial factors influencing colonization of food-producing animals by Salmonella and the basis of host range, differential virulence and zoonotic potential.

Limited genetic diversity and gene expression differences between egg- and non-egg-related Salmonella Enteritidis strains

Salmonella Enteritidis strains of egg- and non-egg-related origin were characterized molecularly to find markers correlated with the egg-contaminating property of Salmonella Enteritidis. Isolates were examined by random amplified polymorphic DNA (RAPD), plasmid profiling and phage typing. Furthermore, the presence of 30 virulence genes was tested by PCR. In genetic fingerprinting and gene content, only small differences between the strains were found and no correlation was observed with the origin (egg-related versus non-egg-related). A major RADP group was present in both egg- and non-egg-related strains, but other smaller RAPD groups were present as well in both categories of strains. Phage types PT4 and PT21 were predominant. Differential mRNA expression levels of fimA and agfA under conditions of growth simulating the conditions during egg formation were determined by real-time RT-PCR. Although differences in fimA and agfA expression levels were observed between the strains, these could not be correlated with the origin of the strains (egg-related versus non-egg-related). The highest expression levels of agfA and fimA were only found in two non-egg-related strains, which seemed to be correlated with the presence of a 93 kb plasmid instead of the 60 kb virulence plasmid. Our results seem to indicate only a limited role for at least type I fimbriae (encoded by fim operon) in egg contamination by Salmonella Enteritidis.

Mechanisms of egg contamination by Salmonella Enteritidis

Salmonella Enteritidis (SE) has been the major cause of the food-borne salmonellosis pandemic in humans over the last 20 years, during which contaminated hen's eggs were the most important vehicle of the infection. Eggs can be contaminated on the outer shell surface and internally. Internal contamination can be the result of penetration through the eggshell or by direct contamination of egg contents before oviposition, originating from infection of the reproductive organs. Once inside the egg, the bacteria need to cope with antimicrobial factors in the albumen and vitelline membrane before migration to the yolk can occur. It would seem that serotype Enteritidis has intrinsic characteristics that allow an epidemiological association with hen eggs that are still undefined. There are indications that SE survives the attacks with the help of antimicrobial molecules during the formation of the egg in the hen's oviduct and inside the egg. This appears to require a unique combination of genes encoding for improved cell wall protection and repairing cellular and molecular damage, among others.

Analysis of the role of 13 major fimbrial subunits in colonisation of the chicken intestines by Salmonella enterica serovar Enteritidis reveals a role for a novel locus

BACKGROUND

Salmonella enterica is a facultative intracellular pathogen of worldwide importance. Over 2,500 serovars exist and infections in humans and animals may produce a spectrum of symptoms from enteritis to typhoid depending on serovar- and host-specific factors. S. Enteritidis is the most prevalent non-typhoidal serovar isolated from humans with acute diarrhoeal illness in many countries. Human infections are frequently associated with direct or indirect contact with contaminated poultry meat or eggs owing to the ability of the organism to persist in the avian intestinal and reproductive tract. The molecular mechanisms underlying colonisation of poultry by S. Enteritidis are ill-defined. Targeted and genome-wide mutagenesis of S. Typhimurium has revealed conserved and host-specific roles for selected fimbriae in intestinal colonisation of different hosts. Here we report the first systematic analysis of each chromosomally-encoded major fimbrial subunit of S. Enteritidis in intestinal colonisation of chickens.

RESULTS

The repertoire, organisation and sequence of the fimbrial operons within members of S. enterica were compared. No single fimbrial locus could be correlated with the differential virulence and host range of serovars by comparison of available genome sequences. Fimbrial operons were highly conserved among serovars in respect of gene number, order and sequence, with the exception of safA. Thirteen predicted major fimbrial subunit genes were separately inactivated by lambda Red recombinase-mediated linear recombination followed by P22/int transduction. The magnitude and duration of intestinal colonisation by mutant and parent strains was measured after oral inoculation of out-bred chickens. Whilst the majority of S. Enteritidis major fimbrial subunit genes played no significant role in colonisation of the avian intestines, mutations affecting pegA in two different S. Enteritidis strains produced statistically significant attenuation. Plasmid-mediated trans-complementation partially restored the colonisation phenotype.

CONCLUSION

We describe the fimbrial gene repertoire of the predominant non-typhoidal S. enterica serovar affecting humans and the role played by each predicted major fimbrial subunit in intestinal colonisation of the primary reservoir. Our data support a role for PegA in the colonisation of poultry by S. Enteritidis and aid the design of improved vaccines.

Salmonella enterica serovar Enteritidis genes induced during oviduct colonization and egg contamination in laying hens

Salmonella enterica serovar Enteritidis is the predominant serovar associated with salmonellosis worldwide, which is in part due to its ability to contaminate the internal contents of the hen's egg. It has been shown that S. enterica serovar Enteritidis has an unusual tropism for the avian reproductive tract and an ability to persist in the oviduct and ovary. Factors allowing S. enterica serovar Enteritidis strains to contaminate eggs could be a specific interaction with the oviduct tissue, leading to persisting oviduct colonization. In vivo expression technology, a promoter-trap strategy, was used to identify genes expressed during oviduct colonization and egg contamination with S. enterica serovar Enteritidis. A total of 25 clones with in vivo-induced promoters were isolated from the oviduct tissue and from laid eggs. Among the 25 clones, 7 were isolated from both the oviducts and the eggs. DNA sequencing of the cloned promoters revealed that genes involved in amino acid and nucleic acid metabolism, motility, cell wall integrity, and stress responses were highly expressed in the reproductive tract tissues of laying hens.

Pathotyping of Salmonella enterica by analysis of single-nucleotide polymorphisms in cyaA and flanking 23S ribosomal sequences

The egg-contaminating phenotype of Salmonella enterica serotype Enteritidis was linked to single-nucleotide polymorphisms (SNPs) occurring in cyaA, which encodes adenylate cyclase that produces cAMP and pyrophosphate from ATP. Ribotyping indicated that SNPs in cyaA were linked to polymorphisms occurring in the rrlC and rrlA 23S ribosomal subunits. Phylogenetic analysis of cyaA discriminated between Salmonella enterica serotypes and within serotype Enteritidis. Serotypes Typhimurium, Heidelberg and Enteritidis produced one, three and six cyaA allelic variants, respectively, among the set of 56 isolates examined. Asparagine(702) of CyaA was converted to serine in a biofilm-producing isolate. Statistical analysis was applied to 42 other genes encoding proteins between 800 and 1000 amino acids (aa). Results show that the 848 aa CyaA of serovar Enteritidis evolved by nucleotide substitutions that did not significantly alter the purine-to-pyrimidine nucleotide substitution ratio, which was a characteristic of large genes that was positively correlated with increasing gene size. In summary, these analyses link SNPs occurring in the rrlC-rrlA genomic fragment of S. enterica to genetic drift within S. Enteritidis that is associated with egg contamination.

Oral immunisation of laying hens with the live vaccine strains of TAD Salmonella vac E and TAD Salmonella vac T reduces internal egg contamination with Salmonella Enteritidis

Eggs are a major source of human infections with Salmonella. Therefore controlling egg contamination in laying hen flocks is one of the main targets for control programmes. A study was carried out to assess the effect of oral vaccination with TAD Salmonella vac E, TAD Salmonella vac T and with both vaccines TAD Salmonella vac E and TAD Salmonella vac T, on colonization of the reproductive tract and internal egg contamination of laying hens with Salmonella Enteritidis. Three groups of 30 laying hens were vaccinated at 1 day, 6 weeks and 16 weeks of age with either one of the vaccine strains, or a combination of both vaccine strains, while a fourth group was left unvaccinated. At 24 weeks of age, the birds were intravenously challenged with 0.5 ml containing 5 x 10(7)cfu Salmonella Enteritidis PT4 S1400/94. The number of oviducts from which Salmonella was isolated, was significantly lower in the vaccinated than in the non-vaccinated hens at 3 weeks post-challenge. Significantly less egg contents were Salmonella positive in the birds vaccinated with TAD Salmonella vac E or TAD Salmonella vac T (12/105 batches of eggs in both groups) than in the unvaccinated birds (28/105 batches of eggs). Internal egg contamination in the hens vaccinated with both TAD Salmonella vac E and TAD Salmonella vac T was even more reduced, as over the whole experiment, only one batch of eggs was positive. In conclusion, these data indicate that vaccination of laying hens with these live vaccines could be considered as a valuable tool in controlling internal egg contamination.

Specific adhesion and invasion of Salmonella Enteritidis in the vagina of laying hens

Salmonella Enteritidis is the predominant serovar associated with egg-borne salmonellosis in humans. The colonization of S. Enteritidis in the vagina may play a role in the production of S. Enteritidis-contaminated eggs. In the first experiment, the in vitro adhesion of S. Enteritidis in vaginal and follicular explants was compared with that of S. Typhimurium by bacteriological isolation methods. The mean number of S. Enteritidis associated with vaginal explants was significantly (P < 0.05) higher than S. Typhimurium associated with vaginal explants and both serovars associated with follicular explants. In the second experiment, the in vitro adhesion and invasion of S. Enteritidis strains in the vaginal epithelium was compared with that of several strains of S. Agona, S. Infantis, S. Hadar, S. Heidelberg, S. Montevideo and S. Typhimurium, by immunohistochemical methods. The mean number of Salmonella in the vaginal epithelium depended on their lipopolysaccharide (LPS) type, with the rank order as follows: LPS type O9 (S. Enteritidis) > LPS type O4 (S. Agona, S. Typhimurium and S. Heidelberg) > LPS type O7 (S. Montevideo and S. Infantis) and LPS type O8 (S. Hadar). This rank order of Salmonella invasiveness is in accordance with the frequency of Salmonella outbreaks involving contaminated eggs. These findings suggest that S. Enteritidis has a higher ability to colonize the vaginal epithelium than other serovars, and the Salmonella LPS type may play an essential role in tropism of the reproductive tract.

Protection of laying hens against Salmonella Enteritidis by immunization with type 1 fimbriae

Eighteen chickens were immunized subcutaneously with purified type 1 fimbriae from Salmonella enterica serotype Enteritidis at 18 and 21 weeks of age. Evidence of IgG and IgA responses was found in the eggs and in the sera of the immunized hens. Three weeks later, immunized and non-immunized chickens (n=18) were challenged intravenously with 2x10(7) live Salmonella enterica serotype Enteritidis. There was no significant difference in the numbers of eggs laid by immunized and non-immunized birds. The percentage of Salmonella contaminated eggs was significantly higher in the non-immunized group than in the immunized group due to a higher percentage of contamination of the externally disinfected egg shells. There were no statistical differences in the percentages of contaminated yolks and egg whites between control and immunized birds. No differences in the number of colonizing bacteria could be found in the spleen nor in the liver between the immunized and the control groups throughout the experiment. Salmonella was cleared from the ovary of the immunized birds in the second week p.i., in contrast to the control birds where Salmonella was isolated till the third week after infection. Oviducts were significantly more infected in the control group than in the immunized group. Salmonella was cleared from the oviducts at 3 weeks p.i. in the immunized hens but not in the control hens. In conclusion, we demonstrated that the immunization of laying hens with type 1 fimbriae reduced the number of contaminated eggs and reduced the colonization of the reproductive organs.