Research to understand and control Salmonella enteritidis in chickens and eggs

Computational modeling and preliminary iroN, fepA, and cirA gene expression in Salmonella Enteritidis under iron-deficiency-induced conditions

Salmonellosis outbreaks in Europe, the United States, and Latin America have been associated with contaminated food derivatives including meat from the poultry industry. Salmonella grown under iron-limiting conditions has the capability to increase concentration of several iron-regulated outer-membrane proteins to augment the acquisition of the metal. These proteins have been proved to have immunogenic properties. Our aim was to increase the relative expression of iroN, fepA, and cirA in Salmonella Enteritidis domestic strain. Furthermore, we proposed a 3-dimensional structure model for each protein to predict and locate antigenic peptides. Our eventual objective is to produce an effective vaccine against regional avian salmonellosis. Two simple factorial designs were carried out to discriminate between 2 nitrogen sources and determine chelating-agent addition timing to augment relative gene expression. Two antigenic peptides located at the external face of each protein and 2 typical domains of iron-regulated outer-membrane proteins, plug and TonB-dep-Rec, were identified from the 3-dimensional models. Tryptone was selected as the best nitrogen source based on growth rate (μx = 0.36 h(-1)) and biomass productivity (Px = 0.9 g•h(-1)•L(-1)) as determined by a general factorial design. Optimum timing for chelating agent addition was in the middle of the log phase, which allowed relative expressions at 4 h of culture. Increase in iroN, fepA, and cirA relative expression was favored by the length of log phase and the addition of chelating agent, which decreased chelating toxicity and enhanced cell growth rate.

Comparison of Salmonella enteritidis phage types isolated from layers and humans in Belgium in 2005

OBJECTIVES

The aim of this study was to investigate the available results for Belgium of the European Union coordinated monitoring program (2004/665 EC) on Salmonella in layers in 2005, as well as the results of the monthly outbreak reports of Salmonella Enteritidis in humans in 2005 to identify a possible statistical significant trend in both populations.

MATERIALS AND METHODS

Separate descriptive statistics and univariate analysis were carried out and the parametric and/or non-parametric hypothesis tests were conducted. A time cluster analysis was performed for all Salmonella Enteritidis phage types (PTs) isolated. The proportions of each Salmonella Enteritidis PT in layers and in humans were compared and the monthly distribution of the most common PT, isolated in both populations, was evaluated.

RESULTS

The time cluster analysis revealed significant clusters during the months May and June for layers and May, July, August, and September for humans. PT21, the most frequently isolated PT in both populations in 2005, seemed to be responsible of these significant clusters. PT4 was the second most frequently isolated PT. No significant difference was found for the monthly trend evolution of both PT in both populations based on parametric and non-parametric methods.

DISCUSSION AND CONCLUSION

A similar monthly trend of PT distribution in humans and layers during the year 2005 was observed. The time cluster analysis and the statistical significance testing confirmed these results. Moreover, the time cluster analysis showed significant clusters during the summer time and slightly delayed in time (humans after layers). These results suggest a common link between the prevalence of Salmonella Enteritidis in layers and the occurrence of the pathogen in humans. Phage typing was confirmed to be a useful tool for identifying temporal trends.

Influence of exogenous melatonin administration on Salmonella enteritidis colonization in molted layers

Two studies were conducted to evaluate the effects of melatonin on Salmonella Enteritidis infection in experimentally challenged laying hens subjected to a forced molt. Leghorn hens (>50 wk of age) were randomly assigned to rooms, acclimated to a 16L:8D regimen, and provided ad libitum access to a nonmedicated mash layer diet and water. Birds in one room were molted (8L:16D; complete feed withdrawal), whereas birds in the second room served as nonmolted controls (CONT). Within each room, birds were randomly assigned to melatonin treatment (MEL; 12 birds/treatment), dosed orally commencing the same day as feed withdrawal for 10 d: (experiment I: 0 or 5 mg of melatonin; experiment II: 0, 10, or 20 mg of melatonin). Three days following feed withdrawal, all birds were experimentally infected with Salmonella Enteritidis, and after 10 d of feed withdrawal, all birds were killed and necropsied. In experiment I, concentrations of Salmonella Enteritidis in the cecal contents and the number of Salmonella Enteritidis-positive tissues from the crop, ceca, liver, spleen, and ovary were higher (P < 0.0001) in the MOLT compared with the CONT treatments. No differences (P > 0.10) were observed in any of the parameters examined due to MEL treatment. For experiment II, cecal concentrations of Salmonella Enteritidis were generally higher in the MOLT compared with the CONT treatment and within molted birds, cecal concentrations were higher in the MEL treatment (P < 0.05). Melatonin treatment in molted birds increased (P < 0.05) the percentage of positive crops in the MOLT+20 MEL treatment (P < 0.05). Salmonella-positive cecal tissue was increased (P < 0.001) in MOLT compared with CONT birds and was also higher in MOLT+10 MEL and MOLT+20 MEL birds compared with the MOLT-only treatment. Results from the current research suggest that dosage with high levels of melatonin may exacerbate Salmonella Enteritidis infection in layers subjected to forced molt.

Emergence of Salmonella serotype Enteritidis phage type 4 in Hawaii traced to locally-produced eggs

OBJECTIVES

In August 1998, the Hawaii Department of Health observed a nine-fold increase in human Salmonella Enteritidis (SE) infections. Isolates were phage type 4 (PT4). An investigation was initiated to determine the source of the outbreak.

METHODS

A matched case-control study enrolled 38 cases. Cases were Hawaii residents with diarrhea and a stool culture yielding SE.

RESULTS

Eating eggs was associated with SE illness; 28 cases (74%) ate eggs in the three days before illness compared to 34 (45%) of 76 controls (MOR=3.0, 95% CI=1.4-7.4). Eighteen (47%) of 38 case patients ate eggs from Farm A compared to 11 (14%) of 76 controls (MOR=12.0, 95% CI=3.1-78.0); the eggs were not properly handled or refrigerated. Cultures from Farm A yielded SE. Human illness subsided following selective flock depopulation.

CONCLUSIONS

This outbreak highlights the importance of proper handling and refrigeration of eggs. The egg industry must implement quality assurance programs to prevent the spread of SE PT4 and human SE illness.

Reduction of Salmonella enterica serovar enteritidis colonization and invasion by an alfalfa diet during molt in Leghorn hens

The standard method for molting to stimulate multiple egg-laying cycles in laying hens is feed deprivation. However, the physiological changes within hens caused by feed deprivation increase susceptibility of the hens to Salmonella enterica serovar Enteritidis (SE) infection. In an effort to develop an alternative method to induce molting without increasing susceptibility to SE, an alfalfa diet was compared with the standard molting method for the level of ovary regression and SE colonization. Hens over 50 wk of age were divided into 3 treatment groups (12 hens/group): nonmolting by normal feeding (NM), molting by feed deprivation (M), and molting by alfalfa diet (A). Individual hens on all treatments were challenged orally with 10(5) cfu of SE on the fourth day after feed changes and were analyzed for ovary weight and SE colonization or invasion in crop contents, cecal contents, liver, spleen, and ovary on the ninth day. In 3 of the 4 trials, there was a significant decrease in SE colonization of the crop between the alfalfa diet (A) and the feed deprived molt (M). In most of the 4 trials, there was a significant reduction in SE infected organs in birds fed the alfalfa diet (A) compared with birds undergoing feed deprived molt (M). Most of the trials showed no significant difference in overall SE between A and NM. Therefore, the results of this study suggest that an alfalfa diet has the potential to be used as an alternative method for forced molting, without increasing the incidence of SE in eggs and internal organs.

Effects of drinking water treatment on susceptibility of laying hens to Salmonella enteritidis during forced molt

Feed deprivation is used in the layer industry to induce molting and stimulate multiple egg-laying cycles in laying hens. Unfortunately, the stress involved increases susceptibility to Salmonella enteritidis (SE), the risk of SE-positive eggs, and incidence of SE in internal organs. Leghorn hens over 50 wk of age were divided into 4 treatment groups of 12 hens each in experiment 1 and 3 treatment groups of 12 hens in experiments 2 and 3; hens were placed in individual laying hen cages. Treatment groups were 1) nonmolted (NM) and received feed and distilled water for 9 d, 2) force molted by feed removal for 9 d and received distilled water, 3) force molted by feed removal for 9 d and received 0.5% lactic acid (LA) in distilled water. An additional group (4) in experiment 1 only was force molted by feed removal for 9 d and received 0.5% acetic acid in distilled water. Seven days before feed removal hens were exposed to an 8L:16D photoperiod, which was continued throughout the experiment. Individual hens among all treatments were challenged orally with 10(4) SE on d 4 of feed removal. When compared with the NM treatments, weight losses were significantly higher in the M treatments, regardless of water treatments. When compared with NM treatments, crop pH was significantly higher in the M treatment receiving distilled water. Crop pH was reduced to that of the NM controls by 0.5% acetic acid in the drinking water. No consistent significant changes were observed for volatile fatty acids. The number of hens positive for SE in crop and ceca after culture and the number of SE per crop and per gram of cecal contents were higher in the M treatments, when compared with the NM treatments, but there was no effect of addition of either of the acids to the drinking water. Additional research using different acid treatment regimens may provide a tool for reducing the incidence of SE in eggs and internal organs during and following molting of laying hens.

Purified beta-glucan as an abiotic feed additive up-regulates the innate immune response in immature chickens against Salmonella enterica serovar Enteritidis

Functionally, the innate immune system of immature chickens is inefficient during the first week posthatch. This immunological inefficiency enables pathogens such as Salmonella enterica serovar Enteritidis (SE) to invade and colonize the visceral organs of immature chickens. The objective of this study was to evaluate the effect of purified beta-glucan as an immunomodulator of the innate immune response. beta-glucan, as a feed additive, significantly provided protection against SE organ invasion in young chickens (P<0.05). The functional efficiency of heterophils isolated from neonatal chickens fed a beta-glucan ration was significantly (P<0.05) up-regulated when compared to heterophils isolated from chickens fed a control ration as determined with an array of functional assays. Phagocytosis, bactericidal killing, and oxidative burst were significantly increased in heterophils isolated from chickens fed the purified beta-glucan ration (P<0.05). To our knowledge, this is the first report of a purified beta-glucan feed additive significantly decreasing the incidence of SE organ invasion in immature chickens and up-regulating the functional abilities of heterophils isolated from immature chickens against an invading pathogen, SE.

The gastrointestinal tract ecology of Salmonella enteritidis colonization in molting hens

There is an interaction between feed withdrawal induced-molting and foodborne Salmonella Enteritidis colonization and invasion in susceptible laying hens. Less is known about the ecology of the indigenous microflora and their response to feed removal, the response of S. Enteritidis to feed removal (virulence expression), and the interaction between the gastrointestinal tract microenvironment and S. Enteritidis. Because the crop is the first host environment encountered by S. Enteritidis after ingestion, it can influence the survival and virulence of S. Enteritidis. Feed withdrawal alters the microenvironment of the crop by causing alterations in the indigenous microbial population along with lactate and short-chain fatty acids (SCFA) concentrations and an increase in pH. This altered crop environment is accompanied by increased S. Enteritidis colonization of the crop and ceca along with invasion of the spleen and liver. The observation that crop composition influences the virulence of S. Enteritidis has important implications for understanding the gastrointestinal factors necessary for protection against S. Enteritidis infection. Consequently, an important aspect for minimizing S. Enteritidis colonization during molting is to maintain the crop microflora and their fermentative activities as similar as possible to that of crop microflora and fermentation activities of birds with fully active gastrointestinal microbial populations.

Optimization of iron supplementation for enhanced detection of Salmonella Enteritidis in eggs

Mixed raw egg contents were inoculated with approximately 10 CFU of Salmonella Enteritidis and supplemented with 0 to 7 mg of FeSO4 per g of egg contents. Egg contents were then incubated at 37 degrees C, and Salmonella Enteritidis colonies were enumerated for up to 106 h. Iron supplementation significantly enhanced the growth of Salmonella Enteritidis. Within the first 24 h of incubation, the optimum iron level for Salmonella Enteritidis growth in egg contents was between 0.2 and 2 mg of FeSO4 per g of egg contents. After 24 h of incubation at 37 degrees C. Salmonella Enteritidis counts in eggs supplemented with 0.5 mg of FeSO4 per g of egg contents consistently reached approximately 1 x 10(9) CFU/ml, whereas Salmonella Enteritidis counts in eggs without iron supplementation varied from less than 5 CFU/ml to 8.4 x 10(6) CFU/ml. A 3 by 3 factorial design was used to study the effect of type of preenrichment and level of iron supplementation on the growth of Salmonella Enteritidis in egg contents. No significant differences in Salmonella Enteritidis counts between preenrichment and nonpreenrichment treatments were observed when egg contents were supplemented with 0.5 mg of FeSO4 per g of egg contents. It was concluded that preenrichment was not necessary for isolation of Salmonella Enteritidis from eggs. The effect of iron supplementation on the sensitivity of detection by the direct plating method was investigated. The direct plating method detected a significantly higher percentage of Salmonella Enteritidis in raw egg contents supplemented with 0.5 mg of FeSO4 per g of egg contents (90%) than in raw egg contents without iron supplementation (63.3%).

Immunopotentiation of a developed Salmonella enterica serotype enteritidis vaccine by thymulin and zinc in meat chicken breeders

The humoral immunity, spleen and thymus weight indices, lymphocyte count in the thymus cortex, and granuloma diameter at vaccination sites were assessed in four differently immunopotentiated groups of meat chicken breeders. Breeders in the first two groups were given a killed Salmonella enterica serotype Enteritidis (SE) vaccine subcutaneously at 15 and 19 weeks of age. Breeders in the third and fourth groups were left unvaccinated. Breeders in the first group were further immunopotentiated with zinc and thymulin. Each bird in the first group was given the immunopotentiators intraperitoneally in a volume of 0.1 ml at intervals of 3 days for a period of 3 weeks, starting at 15 weeks of age. At each time, each bird in the first group received thymulin (10 ng) and ZnCl2 (1 micromol/L), using a carboxymethyl cellulose carrier, totalling 90 ng thymulin and 9 micromol of ZnCl2 per bird. Each bird in the first three groups was challenged orally with 6.7 x 10(6) cfu/ml of highly virulent SE organisms, at an age of 22 weeks. The first group, which had received zinc and thymulin, had the earliest and highest humoral immune response to SE (p<0.05). This was observed at 2 and 4 weeks after the first vaccination. In addition, the first group had the highest mean thymus weight index, and the highest mean lymphocyte count in the thymus cortex. No significant difference was observed between the first two vaccinated groups in the mean granuloma diameter developed at the two vaccination sites 48 h after administration of the vaccine (p>0.05).

Salmonella enteritidis hilA gene fusion response after incubation in spent media from either S. enteritidis or a poultry Lactobacillus strain

The purpose of this study was to determine if growth of a poultry probiotic lactobacilli strain can influence S. enteritidis virulence expression by measuring the response of a hilA-lacZY transcriptional fusion. beta-galactosidase activity was not detected when S. enteritidis was incubated in Lactobacillus-spent medium (24 h growth, pH 4.1, 50.4 mM lactate) but was detectable in spent medium from 4 h growth cultures of Lactobacillus sp. (final OD of 0.213, pH 5.7, 12 mM lactate) when pH and lactate were adjusted to that of the 24 h-pH 4 spent media levels. Adjusting the pH of the 24 h spent medium from 4 to 6, resulted in a measurable beta-galactosidase activity that was significantly higher than expression in LB broth. When S. enteritidis was grown in Salmonella-spent media (24 h growth, pH 4.2, 78 mM acetate), hilA expression was increased 4-fold over expression in the LB broth.

Survival of Yersinia enterocolitica and mesophilic aerobic bacteria on eggshell after washing with hypochlorite and organic acid solutions

Populations of Yersinia enterocolitica 0:9 and mesophilic aerobic bacteria on the shell of fresh chicken eggs were assessed prior and after washing with 0.75%, 1%, and 3% acetic and lactic acids, 50, 100, and 200 mg/liter (ppm) of chlorine, and water. Highest reductions of mesophilic aerobic bacterial populations (normal flora) on trypticase soy agar were 1.28 and 2.15 log10 cycles with 100 and 200 mg/liter of chlorine, 0.28 and 0.36 log10 cycles with 1% and 3% acetic acid, and 0.70 and 0.71 log10 cycles with 1% and 3% lactic acid, respectively, as compared to the control group. No Salmonella or Yersinia were detected among the natural flora of the eggs. On Y. enterocolitica O:9-inoculated eggs, reductions of 2.66, 2.77, and 2.92 log10 cycles by 50, 100, and 200 mg/liter of chlorine, of 2.47, 2.48, and 2.49 log10 cycles by 0.75%, 1%, and 3% of acetic acid, and of 2.48 and 2.72 log10 cycles with 1% and 3% of lactic acid, respectively, were observed with respect to the control. Organic acids at 3% caused detachment of the surface cuticle of the eggshell. Y. enterocolitica was more sensitive to the wash treatments than the natural microflora. The absence of potentially pathogenic Y. enterocolitica, observed for other fresh foods, should be a norm for fresh eggs sold in retail stores.

Salmonella enteritidis: the egg and I

The world-wide clinical incidence of Salmonella Enteritidis has increased markedly. The increase is associated with the enhanced ability of the bacterium to systemically colonise layer chickens. Subsequent contamination and consumption of intact shell eggs from colonised layer hens, either directly or in foods containing raw or lightly cooked eggs, causes human disease. Despite investigation, no change in the biology of the bacterium has been correlated with increased colonisation in chickens. To date, no method of control at the production level has proven effective; consumer education is the best means of minimising the public health risk.

Effect of Eimeria tenella infection on Salmonella enteritidis infection in chickens

The effect of Eimeria tenella infection on the Salmonella enteritidis infection in chickens was investigated in three experiments. Each experiment consisted of an uninfected control, birds infected with E. tenella, birds infected with S. enteritidis, and birds infected with a combination of E. tenella and S. enteritidis. A dose of 2 x 10(4) sporulated oocysts of E. tenella was given to each chicken. In Experiment 1, each chicken was infected with 10(5) cfu/d of S. enteritidis for 3 consecutive d starting 1 d after coccidia exposure and necropsied 4, 7, 10, and 14 d after coccidial infection. In Experiments 2 and 3, each bird was infected with 10(2) cfu/d and 10(1) cfu/d of S. enteritidis respectively, for 2 d beginning 4 d after coccidia exposure, and were killed 7, 10, and 14 d postinfection with E. tenella. Results showed that interaction between S. enteritidis and E. tenella was significant in Experiments 1 and 2, but not in Experiment 3, manifesting that the cecal Salmonella population were significantly increased by coccidial infection in birds killed 4, 10, or 14 d after coccidia exposure in Experiment 1 and in birds killed 14 d after coccidial infection in Experiment 2. The dose size of S. enteritidis was an important factor for the synergistic relationship between S. enteritidis and E. tenella. Frequency of recovery of S. enteritidis in liver and spleen was not increased by E. tenella infection.

In ovo administration of Salmonella enteritidis-immune lymphokines confers protection to neonatal chicks against Salmonella enteritidis organ infectivity

We previously reported that the prophylactic, intraperitoneal administration of supernatants from concanavalin A-stimulated T cells derived from Salmonella enteritidis (SE)-immune White Leghorn hens (i.e., SE-immune lymphokines or ILK), conferred protection to neonatal White Leghorn chicks against SE organ invasion. In the present study, we evaluated the effects of in ovo administration of ILK on hatchability, hatch weight, in vitro bactericidal activity of heterophils, and protection against SE organ invasion in neonatal White Leghorn chicks. On Day 18 of embryogenesis, injections were made into the amnion with either ILK or nonimmune ILK (NILK) or were not injected (untreated). On the day of hatch, whole blood was collected from 20 of the chicks per treatment group for heterophil isolation. All remaining chicks were orally challenged with 5 x 10(4) cfu SE. Twenty-four hours after SE challenge, organs (liver and spleen) from the chicks were cultured for SE. Hatchability of ILK- and NILK-treated chicks was not different from that of untreated chicks. Hatch weights of ILK-treated chicks were approximately 1 g less (P < .05) than that of NILK-treated or untreated chicks. In vitro bactericidal activity of peripheral blood heterophils derived from ILK-treated chicks was increased (P < .05) above activity from heterophils derived from NILK-treated or untreated chicks. Organ invasion with SE was markedly and significantly decreased in the ILK-treated chicks as compared with chicks treated with NILK or untreated chicks. These results suggest that in ovo administration of ILK confers protection to neonatal chicks against SE organ infectivity at hatch.

Detection of Salmonella typhimurium in dairy products with flow cytometry and monoclonal antibodies

Flow cytometry, combined with fluorescently labelled monoclonal antibodies, offers advantages of speed and sensitivity for the detection of specific pathogenic bacteria in foods. We investigated the detection of Salmonella typhimurium in eggs and milk. Using a sample clearing procedure, we determined that the detection limit was on the order of 10(3) cells per ml after a total analysis time of 40 min. After 6 h of nonselective enrichment, the detection limits were 10 cells per ml for milk and 1 cell per ml for eggs, even in the presence of a 10,000-fold excess of Escherichia coli cells.