Understanding Salmonella enteritidis in laying chickens: the contributions of experimental infections

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

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

Genomic Characterization of a Nalidixic Acid-Resistant Salmonella Enteritidis Strain Causing Persistent Infections in Broiler Chickens

Virulent strains of Salmonella enterica subsp. enterica serovar Enteritidis (SE) harbored by poultry can cause disease in poultry flocks and potentially result in human foodborne illness. Two broiler flocks grown a year apart on the same premises experienced mortality throughout the growing period due to septicemic disease caused by SE. Gross lesions predominantly consisted of polyserositis followed by yolk sacculitis, arthritis, osteomyelitis, and spondylitis. Tissues with lesions were cultured yielding 59 SE isolates. These were genotyped by Rep-PCR followed by whole-genome sequencing (WGS) of 15 isolates which were clonal. The strain, SE_TAU19, was further characterized for antimicrobial susceptibility and virulence in a broiler embryo lethality assay. SE_TAU19 was resistant to nalidixic acid and sulfadimethoxine and was virulent to embryos with 100% mortality of all challenged broiler embryos within 3.5 days. Screening the SE_TAU19 whole-genome sequence revealed seven antimicrobial resistance (AMR) genes, 120 virulence genes, and two IncF plasmid replicons corresponding to a single, serovar-specific pSEV virulence plasmid. The pef, spv, and rck virulence genes localized to the plasmid sequence assembly. We report phenotypic and genomic features of a virulent SE strain from persistently infected broiler flocks and present a workflow for SE characterization from isolate collection to genome assembly and sequence analysis. Further SE surveillance and investigation of SE virulence in broiler chickens is warranted.

Can a combination of vaccination, probiotic and organic acid treatment in layer hens protect against early life exposure to Salmonella Typhimurium and challenge at sexual maturity?

Day old layer chicks were challenged with Salmonella Typhimurium using a seeder bird technique. Treatment groups were untreated control, administration of a probiotic in drinking water weekly, vaccination by intramuscular injection of a live aro-A deletion mutant vaccine at 10 weeks of age (woa) followed by an oral dose at 16 woa, probiotic administration plus vaccination, vaccination plus the administration of an organic acid preparation in feed from 16 woa and a combination of probiotic, vaccine and organic acid. Faecal shedding was monitored by culture at 1, 2, 3, 4, 8, 12, 15, 17, 20, 21, 23 and 25 woa and in dust from settle plates by PCR at intervals from 8 woa. Birds from each group were separated at 17 and 18 woa and challenged orally with 10⁶ CFU of S. Typhimurium. Both untreated and probiotic groups shed Salmonella until 56 days. Salmonella was also detected in dust from 8 until 12 woa but little after this. After vaccination, from sexual maturity (18 woa) all groups except those that were vaccinated with and without probiotic re-excreted Salmonella. The probiotic alone was ineffective against this re-excretion and all groups receiving organic acids shed Salmonella. At 17 woa, unchallenged controls were fully susceptible to caecal colonization, however all other groups showed reduced susceptibility, including the untreated challenged group. However, at 18 woa (sexual maturity) only the groups that were vaccinated with or without probiotic showed reduced susceptibility to colonization. The organic acid treated groups (including the vaccinated group) did not show a difference to the untreated controls. S. Typhimurium demonstrated an ability to re-emerge at sexual maturity, similar to other serovars. The vaccine assisted in limiting the re-excretion at sexual maturity and decreased susceptibility to subsequent challenge. Use of a probiotic augmented the vaccine's protective capacity.

Phenotypic analyses of Salmonella enterica serovar Enteritidis strains isolated in the pre- and post-epidemic period in Brazil

Salmonella Enteritidis has caused, since the 1980s, a sustained epidemic of human infections in many countries. This study analyzed S. Enteritidis strains isolated before and after the epidemic period in Brazil regarding their capacities to survive to acid, oxidative, and high-temperature stresses, and capacity to grow in egg albumen. Moreover, the ability to invade human epithelial cells (Caco-2) and to survive inside human (U937) and chicken (HD11) macrophages was checked. Post-epidemic strains showed a better ability to survive after 10 min under acid stress at 37 °C (P ≤ 0.05). However, both groups of strains showed similar ability to survive after 1 h under acid stress at 37 °C and at 42 °C independently of the time of exposure. Similar ability was verified in both groups of strains regarding oxidative stress, growth in egg albumen, high-temperature stress, invasion to Caco-2 cells, and invasion and survival in macrophages. In conclusion, post-epidemic S. Enteritidis strains showed a better ability to survive under the acid stress found in the stomach, which might be an advantage to reach the intestine and colonize chickens and humans. However, both groups of strains did not differ significantly in the majority of the phenotypic tests analyzed in this study.

Effects of a mannan-rich yeast cell wall-derived preparation on cecal concentrations and tissue prevalence of Salmonella Enteritidis in layer chickens

Salmonella Enteritidis (SE) has been the most common Salmonella serotype associated with foodborne infections in the last several years. Dietary applications of yeast-based preparations in feed have shown to reduce Salmonella colonization in chickens augmenting SE control strategies. This study was conducted to evaluate the effects of a mannan-rich yeast cell wall-derived preparation (Actigen^®) administered in feed at a rate of 400 g/ton on SE colonization in the cecum and internal organs of commercial layer chickens. Sixteen week-old layer pullets were orally challenged with a selected nalidixic acid resistant SE strain at a dose of 1.7×10^9 colony forming units (CFU) per bird. SE colonization was assessed by evaluating isolation rates from ovary and pooled liver/spleen samples as well as enumeration of SE in cecal pouches one week post-challenge. Recovery rates of SE from the ovaries of directly challenged birds receiving Actigen^® were significantly lower (P <0.02) than those in directly challenged birds fed an unsupplemented control diet. Recovery rates of SE from pooled liver/spleen samples were not significantly different between Actigen^®-treated pullets and controls (P = 0.22). Using direct plate count methods, cecal SE concentrations were 1 log₁₀ lower (P <0.001) in challenged pullets in the Actigen^®-supplemented group than in the challenged controls. The SE concentration distributions in the ceca were similar in groups testing positive and groups testing negative for SE in the ovaries and liver/spleens tissues. As a result, SE concentrations in the ceca could not be directly related to the occurrence or prevalence of SE in these tissues. In conclusion, Actigen^® supplementation appears to decrease the prevalence of SE in ovarian tissue and concentrations of SE in cecal contents and may be useful as a tool for reducing the risk of eggshell contamination and transovarian transmission of SE in eggs.

Observations on the distribution and control of Salmonella in commercial duck hatcheries in the UK

Salmonella infection causes a significant number of cases of gastroenteritis and more serious illnesses in people in the UK and EU. The serovars Salmonella Enteritidis and Salmonella Typhimurium are most frequently associated with foodborne illness in Europe. Whilst control programmes exist to monitor these serovars in the chicken and turkey sectors, no regulatory programme is currently in place for the duck sector. A voluntary industry scheme (Duck Assurance Scheme) was launched in the UK in 2010. Hatcheries act as focal points of Salmonella contamination, in particular if Salmonella-contaminated eggs from positive breeding farms enter the hatchery. Five duck hatcheries were visited in this study and four were positive for Salmonella. S. Typhimurium DT8 and S. Indiana were isolated from hatchery 1 and S. Typhimurium DT41 and S. Senftenberg were isolated from hatchery 3. S. Kottbus, S. Bovismorbificans and S. Senftenberg were isolated from hatchery 2 and S. Kedougou was isolated from hatchery 4. Advice on the control/elimination of Salmonella was provided at each visit and a longitudinal study was undertaken to monitor its effectiveness. Extensive sampling was carried out in the hatcheries visited and the tray wash area and waste/external areas had the highest probability of being contaminated. The hatcher area was also found to be a primary focus of contamination. Improvements of farm and hatchery biosecurity standards have resulted in a reduction of hatchery contamination in this study and in previous investigations. Hatcheries 1 and 5 were cleared of Salmonella, demonstrating that elimination of Salmonella contamination from duck hatcheries is achievable.

Effects of bacteriophage supplementation on egg performance, egg quality, excreta microflora, and moisture content in laying hens

An experiment was conducted to evaluate the effects of bacteriophage supplementation on egg performance, egg quality, excreta microflora, and moisture content in laying hens. A total of 288 Hy-line brown commercial laying hens (36-wk-old) were randomly allotted to 4 treatments in this 6-wk trial and dietary treatments included: i) CON, basal diet; ii) T1, CON+0.020% bacteriophage; iii) T2, CON+0.035% bacteriophage; iv) T3, CON+0.050% bacteriophage. There were 6 replicates for each treatment with 6 adjacent cages (2 hens/cage). Laying hens in T2 and T3 treatments had higher (p<0.05) egg production than those in CON and T1 treatments during wk 0 to 3. In addition, egg production in T1, T2, and T3 treatments was increased (p<0.05) compared with that in CON treatment during wk 4 to 6. At wk 4 and 5, birds in T2 group had higher (p<0.05) HU than those in CON. In addition, at wk 5 and 6, HU in birds fed T1 and T3 diets was greater (p<0.05) than those fed CON diet. E. coli and Salmonella spp. concentrations in excreta were decreased (p<0.05) by T1, T2, and T3 treatments. However, egg weight, egg shell color, yolk height, yolk color unit, egg shell strength, egg shell thickness, egg gravity, and excreta moisture content were not influenced by dietary treatments during the entire experimental period. In conclusion, bacteriophage supplementation has beneficial effects on egg production, egg albumen, and excreta microflora concentration in laying hens.

Systemic administration of lipopolysaccharide in laying hens stimulates antimicrobial properties of egg white against Staphylococcus aureus

The natural protective system of eggs relies on egg yolk immunoglobulins and on antimicrobial proteins/peptides mainly concentrated in the egg white. There is much evidence concerning the specific stimulation of immunoglobulins by antigens but to date, the influence of the hen milieu on the regulation of the egg innate molecular immunity has not been established. To explore the hypothesis of modulation in egg antimicrobial molecules, laying hens were immune-challenged with intravenous injections of Salmonella enterica Enteritidis lipopolysaccharide (LPS) at 24 h intervals. Eggs of the control and LPS groups were collected over a period of 21 days following the first LPS injection and the egg white activities against Staphylococcus aureus and Escherichia coli were assessed. The increase in egg white anti-S. aureus activity reached 20.9% and 23.4% (p<0.05) respectively on days 5 and 6 after the first LPS injection. Anti-E. coli activity increased moderately only on days 9 and 15 after the LPS treatment. To explore the origin of these increased antimicrobial activities, we analyzed the lysozyme and proteases inhibiting (anti-trypsin and anti-chymotrypsin) activities and the pH variations of egg whites. We recorded no significant variations between the two experimental groups for these potential modulating factors. Finally, using RT-qPCR we studied the expression of several genes coding for antimicrobial proteins and peptides involved in the immune response in the infundibulum and the magnum, Out of the 11 genes, only TLR4 in the magnum and ovocalyxin-36 in infundibulum were over-expressed respectively 24h and 8 days after the first LPS injection. The other candidate genes showed similar or down regulated expression in the LPS group as compared to the control especially during the first 24h. Our results suggest that the hen enhances the albumen antimicrobial activity of its eggs when exposed to immune stimulations or infections. This could be an attempt to preventively reinforce the protection of the embryo with nonspecific antimicrobial agents in addition to the specific antibodies exported to the egg. The origin of this stimulation of egg molecular immunity remains to be characterized amongst the numerous novel egg proteins recently identified.

Salmonella Enteritidis strains from poultry exhibit differential responses to acid stress, oxidative stress, and survival in the egg albumen

Salmonella Enteritidis is the major foodborne pathogen that is primarily transmitted by contaminated chicken meat and eggs. We recently demonstrated that Salmonella Enteritidis strains from poultry differ in their ability to invade human intestinal cells and cause disease in orally challenged mice. Here we hypothesized that the differential virulence of Salmonella Enteritidis strains is due to the differential fitness in the adverse environments that may be encountered during infection in the host. The responses of a panel of six Salmonella Enteritidis strains to acid stress, oxidative stress, survival in egg albumen, and the ability to cause infection in chickens were analyzed. This analysis allowed classification of strains into two categories, stress-sensitive and stress-resistant, with the former showing significantly (p<0.05) reduced survival in acidic (gastric phase of infection) and oxidative (intestinal and systemic phase of infection) stress. Stress-sensitive strains also showed impaired intestinal colonization and systemic dissemination in orally inoculated chickens and failed to survive/grow in egg albumen. Comparative genomic hybridization microarray analysis revealed no differences at the discriminatory level of the whole gene content between stress-sensitive and stress-resistant strains. However, sequencing of rpoS, a stress-regulatory gene, revealed that one of the three stress-sensitive strains carried an insertion mutation in the rpoS resulting in truncation of σ(S). Finding that one of the stress-sensitive strains carried an easily identifiable small polymorphism within a stress-response gene suggests that the other strains may also have small polymorphisms elsewhere in the genome, which likely impact regulation of stress or virulence associated genes in some manner.

Phenotypic and molecular characterization of Salmonella enterica serovar Sofia, an avirulent species in Australian poultry

Salmonella enterica serovar Sofia (S. Sofia) is often isolated from chickens in Australia. However, despite its high frequency of isolation from chicken and chicken meat products, S. Sofia is rarely associated with animal or human salmonellosis, presumably because this serovar is avirulent in nature. The objective of this work was to investigate the phenotypic and molecular properties of S. Sofia in order to assess its pathogenic potential. Our in vivo studies support the observation that this serovar can colonize tissues, but does not cause disease in chickens. This was further confirmed with tissue culture assays, which showed that the ability of S. Sofia to adhere, invade and survive intracellularly is significantly diminished compared with the pathogenic Salmonella enterica serovar Typhimurium (S. Typhimurium) 82/6915. Molecular analysis of Salmonella pathogenicity islands (SPIs) showed that most of the differences observed in SPI1 to SPI5 of S. Sofia could be attributed to minor changes in the sequences, as indicated by a loss or gain of restriction cleavage sites within these regions. Sequence analysis demonstrated that the majority of virulence genes identified were predicted to encode proteins sharing a high identity (75–100 %) with corresponding proteins from S. Typhimurium. However, a number of virulence genes in S. Sofia have accumulated mutations predicted to affect transcription and/or translation. The avirulence of this serovar is probably not the result of a single genetic change but rather of a series of alterations in a large number of virulence-associated genes. The acquisition of any single virulence gene will almost certainly not be sufficient to restore S. Sofia virulence.

Enterobacteriaceae associated with eggs of Podocnemis expansa and Podocnemis unifilis (Testudines:Chelonia) in nonpolluted sites of national park of Araguaia Plains, Brazil

Fertile eggs of Podocnemis expansa and Podocnemis unifilis were investigated for the presence of enterobacteria, as these two endangered species have the potential for conservation measures that include egg transfer. Knowledge of normal microflora associated with turtles and turtle eggs would help effectively manage the transfer of these eggs among institutions. Thirty eggs of each species were collected, aseptically transferred, cracked inside plastic bags containing tetrathionate broth, and spread on selective media plates. Ten samples of sand and water were also examined for the presence of fecal coliforms using Colilert Quanti-Tray kits. Enterobacteriaceae were identified using an API 20E biochemical test kit. A majority of the bacteria isolated were potential pathogens. All egg samples were positive for Enterobacteriaceae, among which 15 eggs of P. expansa were positive for Shigella flexneri. Other isolates included Chromobacterium violaceum, Escherichia coli, and Aeromonas salmonicida subsp. salmonicida. Eggs of P. unifilis were most frequently positive for Shigella flexneri and C. violaceum, and less frequently positive for A. salmonicida subsp. salmonicida and Salmonella choleraesuis subsp. arizonae. The source of the bacteria in these eggs is unknown, but the nesting beaches were considered a source as water samples had low total coliform counts and E. coli was isolated from only one sand sample. This study demonstrated that Enterobacteriaceae are part of the indigenous microflora of chelonians.

Toward better control of Salmonella contamination by taking advantage of the egg's self-defense system: a review

Egg-associated salmonellosis is a major problem for food safety. It can be caused by vertical transmission (transovarian transmission) in hens and horizontal transmission though penetration. Despite a series of physical and chemical defense mechanisms naturally found in eggs, they cannot provide complete protection for them. Environmental hygiene, bacteria vectors such as birds, rodent, flies, and beetles along with feed and water contamination are the most frequently reported causes of Salmonella colonization in hens, and finally to eggs. In addition, inappropriate egg handling will cause eggs to lose their self-protection ability, thus resulting in the survival and multiplication of Salmonella in an egg's contents, which contributes to the horizontal dissemination. The routes of Salmonella contamination were discussed, and the effectiveness and shortcomings of different decontamination methods were evaluated in this review. Various studies on egg storage indicated that the low-temperature storage without temperature fluctuation was beneficial for the control of Salmonella. This review, based on an understanding of the stages of Salmonella transmission and an egg's self-protection mechanisms, highlights a comprehensive strategy toward Salmonella control in a process from egg production and handling to human consumption.

A time-course study of gene responses of chicken granulosa cells to Salmonella Enteritidis infection

Consumption of eggs contaminated with Salmonella Enteritidis (SE) has been recognized as one of the important causes of human foodborne salmonellosis. Chicken granulosa cells (cGCs) comprise the last tissue layer surrounding the yolk in preovulatory follicles and are a preferred site for SE invasion. To understand the cGC response to SE infection, we conducted an in vitro time-course study to identify cGC transcriptional changes using chicken whole genome microarrays. The expression of 135 (4h postinfection) and 120 cGC genes (48 h postinfection) were altered (P<.01) compared to uninfected cells. Many of the altered genes were related to immune response, physiological processes, signal transduction, and transcription. Furthermore, we also found that the Jak-STAT pathway, which is essential in the regulation of cellular cytokines and growth factors, was highly active in this study. Among the genes identified by microarray, the mRNA levels of TLR15, IL-6, CXCLi1, CXCLi2, and K203 were shown to be upregulated by real-time RT-PCR (qRT-PCR). In contrast, the mRNA levels of RASD1 and HB-EGF decreased according to both microarray and qRT-PCR analyses. These results suggest that during the SE infection, cGCs recruit cells of the innate immune responses; the infection may also induce suppression of cGC cell proliferation, which alters follicular development and ovulation.

Bacterial flora and antibiotic resistance from eggs of green turtles Chelonia mydas: an indication of polluted effluents

Sea turtles migrate to various habitats where they can be exposed to different pollutants. Bacteria were collected from turtle eggs and their resistance to antibiotics was used as pollutant bio-indicators of contaminated effluents. Eggs were collected randomly from turtles when they were laying their eggs. A total of 90 eggs were collected and placed into sterile plastic bags (3 eggs/turtle) during June-December of 2003. The bacteria located in the eggshell, albumen and yolk were examined, and 42% of the eggs were contaminated with 10 genera of bacteria. Pseudomonas spp. were the most frequent isolates. The albumen was found to be the part of the egg to be the least contaminated by bacterial infection. Bacterial isolates tested with 14 antibiotics showed variations in resistance. Resistance to ampicillin was the highest. The presence of antibiotic resistant bacteria in eggs indicates that the green turtle populations were subjected to polluted effluents during some of their migratory routes and feeding habitats. Scanning electron microscopy revealed that Salmonella typhimurium penetrated all eggshell layers.

Dissemination and tracking of Salmonella spp. in integrated broiler operation

Controlling Salmonella in integrated broiler operation is complicated because there are numerous potential sources of Salmonella contamination, including chicks, feed, rodents, wild poultry operations, and the processing plant. The objective of this study was to investigate the distribution of Salmonella through all phases of two integrated broiler operations and to determine the key areas related to the control of all known sources of infection. Two different Salmonella serotypes were observed at integrated broiler chicken company A. S. enteritidis, the predominant company A isolate, was consistently found in the breeder farm, hatcheries, broiler farms, and chicken slaughterhouse. At company B, a total of six different serotypes, S. heidelberg, S. senftenberg, S. enteritidis, S. blockley, S. gallinarum, and S. virchow, were detected. Although S. heidelberg was not found in the broiler farms, it was consistently found in the breeder farm, hatcheries, and chicken slaughterhouse. In addition, S. enteritidis was found in the hatcheries, broiler farm, and chicken slaughterhouse. In order to obtain the genetic clonality, 22 S. enteritidis isolates were digested with XbaI and analyzed by pulsed-field gel electrohporesis (PFGE). A difference in the PFGE pattern was found to be related to the origin of the integrated broiler operation. These data support the critical need to control Salmonella in breeder farms and hatcheries, and demonstrate important points related to the control of infection in large-scale poultry operations of Korea.

In vitro anaerobic incubation of Salmonella enterica serotype Typhimurium and laying hen cecal bacteria in poultry feed substrates and a fructooligosaccharide prebiotic

The objective of this study was to investigate the effect of combining a prebiotic with poultry feeds on the growth of Salmonella enterica serotype Typhimurium (ST) in an in vitro cecal fermentation system. Cecal contents from three laying hens were pooled and diluted to a 1:3000 concentration in an anaerobic dilution solution. The cecal dilution was added to sterile test tubes filled with alfalfa and layer ration with and without fructooligosaccharide (FOS). Two controls containing cecal dilutions and anaerobic dilution solution were used. The samples were processed in the anaerobic hood and incubated at 37 degrees C. Samples were inoculated with Salmonella at 0 and 24h after in vitro cecal fermentation and plated at 0 and 24h after inoculation with ST. Plates were incubated for 24h and colony forming units (CFU) enumerated. The samples immediately inoculated with ST without prior cecal fermentation did not significantly lower ST counts 24h later. However, samples pre-incubated for 24h with cecal microflora prior to ST inoculation exhibited reduced ST CFU by approximately 2 logarithms, with the most dramatic decreases seen in alfalfa and layer ration combined with FOS. The addition of FOS to feed substrate diets in combination with cecal contents acted in a synergistic manner to decrease ST growth only after ST was introduced to 24h cecal incubations.

Competitive exclusion against Salmonella Enteritidis in layer chickens by yoghurt microbiota: impact on egg production, protection and yolk-antibody and cholesterol levels

AIMS

This work aims at studying the impact of competitive exclusion of Salmonella serotype Enteritidis infection in layer chickens, by microbiota of fresh and dried-modified yoghurt, on egg production and weight, protection against infection, and on yolk-antibody and cholesterol levels.

METHODS AND RESULTS

Four groups of 27-week-old layer chickens were included in this study. After an initial enrofloxacin treatment, groups 1 and 2 were administered fresh or dry yoghurt (respectively) for 14 days. Groups 1, 2 and 3 were challenged intraoesophageally with Salm. Enteritidis, on the sixth day of yoghurt administration, while group 4 was left unchallenged and without yoghurt administration. No significant difference in percent infectivity of visceral organs with Salm. Enteritidis was observed between the groups. The yoghurt administered groups showed an early significant antibody response in their yolk on the seventh day postchallenge (P < 0.05) and highest egg production and weight. Finally, the egg yolk cholesterol concentration was higher in Salm. Enteritidis-challenged groups than that observed in the unchallenged group.

CONCLUSIONS

The results point to the possible involvement of yoghurt administration in immunopotentiation and improvement of egg production and weight.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings warrant further research that could improve immunity and production in layer chickens infected with Salm. Enteritidis.

Characterization of Salmonella spp. Isolated from an Integrated Broiler Chicken Operation in Korea

The purpose of this study was to investigate the biological and genetic characterization of persistent Salmonella isolates in an integrated broiler chicken operation, in an attempt to elucidate the source of contamination. From the breeder farm, the hatchery, the broiler farm and the chicken slaughter house of an integrated broiler chicken operation, a total of 6 serotypes were observed. Although S. Heidelberg was not detected in the broiler farm, it was consistently found in the breeder farm, the hatchery and the chicken slaughter house. Also, S. Enteritidis and S. Senftenberg were found in the hatchery and the chicken slaughter house, and the hatchery and the broiler farm, respectively. S. Gallinarum and S. Blockley were found only in the broiler farm, and S. Virchow was only recovered in the chicken slaughter house. Isolated S. Heidelberg, S. Enteritidis and S. Senftenberg strains were divided into 3, 5 and 7 types, respectively, on the basis of all properties. Especially, S. Senftenberg isolates, divided into four types by their antimicrobial resistance patterns, were all obviously the XbaI PFGE pattern. Also, four S. Enteritidis isolates resistant to nalidixic acid showed a difference in phage type and PFGE pattern. Such a different pattern was shown despite Salmonella isolates originating from an integrated broiler operation, suggesting that further epidemiological studies on many integrated chicken companies in Korea are needed.

Phenotypic and genotypic changes in Salmonella enterica subsp. enterica serotype typhimurium during passage in intestines of broiler chickens fed on diets that included ionophore anticoccidial supplements

The effect of continuous in-feed administration of anticoccidial agents on antimicrobial sensitivity and the level of bacterial shedding in poultry experimentally infected with Salmonella enterica subsp. enterica serotype Typhimurium definitive type 104 (DT104) were investigated. On day 0, 1,200 1-day-old Salmonella-free broiler chicks were placed into 50 pens, and the pens were randomly allocated to one of five treatments: nonsupplemented (negative control; T1), monensin at 120 mg/kg of diet (T2), salinomycin at 60 mg/kg of diet (T3), semduramicin at 20 mg/kg of diet (T4), or semduramicin at 25 mg/kg of diet (T5). Each bird was inoculated with a well-characterized strain of serotype Typhimurium DT104 on day 10. On day 49, the birds were euthanatized humanely. Bulk fecal samples were collected on days 13, 43, and 48 and were examined for organisms which had acquired resistance. The genetic basis of acquired resistance was determined from representative samples of isolates. Of 784 Salmonella-selective plates supplemented with antimicrobial agents, only 33 showed growth. These isolates came from all treatment regimens, including the nonsupplemented control. A number of phenotypic changes were observed; these included changes in motility, phage type, and agglutination properties. Supplementation of the diet with an anticoccidial drug does not appear to affect antimicrobial resistance or the level of excretion of salmonellae. Most of the changes observed do not seem to be related to the presence of a supplement in feed. Salmonellae appear to be capable of acquiring antimicrobial resistance and phenotypic changes independently of specific antimicrobial selection pressures.

Evaluation of treatment and prophylaxis with nitrofurans and comparison with alternative antimicrobial agents in experimental Salmonella enterica Serovar enteritidis infection in chicks

The ability of the nitrofuran antimicrobial agents furazolidone and furaltadone to prevent, reduce or eliminate Salmonella enterica serovar enteritidis PT4 infection in artificially challenged day-old chicks was evaluated. Treating the birds with the nitrofurans failed to eliminate established infections with either furazolidone-resistant (FzR) or furazolidone-sensitive (FzS) strains. Simultaneous administration of the nitrofurans to day-old chicks challenged with FzS failed to prevent infection but reduced colonization significantly (p<0.05) compared to unmedicated controls. No reduction of colonization occurred with FzR. Challenging birds with FzS and simultaneous dosing with nitrofurans for 1 week, followed by a second week of continued treatment, resulted in an increase in the level of colonization in the second week rather than a decrease. Dosing with the nitrofurans (200 ppm) for 1 week prior to challenge with FzS and continued medication for a further week prevented colonization of the caecum, liver and spleen. However, cessation of dosing at the time of challenge with salmonella resulted in colonization. Chloramphenicol and tetracycline at concentrations of 200 ppm were both independently capable of preventing colonization by salmonella. Sulphadiazine initially reduced colonization but failed to eliminate the infection. Only when furazolidone was combined with chloramphenicol or when sulphadiazine was combined with trimethoprim, and the combined drugs were administered concurrently with the challenge, was colonization prevented.

Microbial contamination in inoculated shell eggs: I. Effects of layer strain and hen age

Three Ottawa control strains and a current commercial laying stock were reared and housed under identical environmental and management conditions. Eggs were collected from each strain when hens were 32, 45, 58, 71, and 84 wk of age. The eggs were inoculated with Salmonella enteritidis (SE), Pseudomonasfluorescens (PF), or a combination of the two. After storage at 26 C, bacterial counts were obtained from the exterior shell surfaces (rinse), air cell, egg contents, and shell structure. SE and PF survived at different rates on the shell surface with as much as a 1 log difference during a given collection period. Egg content counts tended to be higher than eggshell counts in PF, whereas the opposite was true for SE. These data suggest that PF is a primary invader of eggs that is more capable of contaminating egg contents through the shell membranes than SE. The PF and SE data suggest that bacterial contamination of air cells, shells, and egg contents is more easily achieved in eggs from older hens than from younger hens. There were also differences between the strains. Control Strain 10 consistently maintained a lower level of contamination for both organisms in each sampling location. The overall results of this study suggest that genetic selection has altered the ability of eggs to resist microbial contamination and that screening for microbial integrity should be considered in the selection process among the laying egg breeders.

Sobrevivência de Salmonella enteritidis em Ovos Contaminados Artificialmente, Após Desinfecção e Armazenados em Diferentes Temperaturas

Avaliou-se a contaminação da casca e do conteúdo interno de ovos inoculados com Salmonella enterica sorovar enteritidis fagotipo 4, lavados com água de torneira (AT) ou solução de amônia quaternária (AQ) e armazenados a 8ºC e 25ºC. Duzentos e cinqüenta e dois ovos foram divididos em três grupos. Os tratamentos de cada grupo consistiram de imersão em AT, AQ a 25ºC e a 43ºC. Após a secagem natural, todos os grupos foram contaminados com solução de S. enteritidis. Seguindo-se a contaminação, cada grupo tratado foi estocado a 8ºC ou 25ºC, e a presença de S. enteritidis na casca e no conteúdo interno foi avaliada após zero, 24, 96 e 168 horas. A sanitização com AQ mostrou-se eficiente na redução de S. enteritidis nas cascas dos ovos. O armazenamento dos ovos a 8ºC demonstrou ser preponderante na redução e na ausência de S. enteritidis na casca. Nos ovos lavados com AT, o armazenamento a 25ºC permitiu a permanência da bactéria nas cascas até 168 horas. Não se detectou S. enteritidis no conteúdo interno dos ovos em nenhum dos grupos.

The first Salmonella enteritidis phage type 1 infection of a commercial layer flock in Finland

The first Salmonella Enteritidis phage type (PT) 1 infection in a commercial layer flock of 2700 birds in Finland occurred in 1995. All the birds were ordered to be killed, the eggs to be destroyed and access to the layer house was denied in order to prevent spread of the infection. Ninety one commercial layers, 61 replacement pullets and 1062 eggs were collected for the analyses. The total infection level of the flock was 8%, concentrated on the 2 older age groups. S. Enteritidis PT1 was isolated from livers (5%), ovaries (2%) and from caeca (3%), of which 2 positive samples were detected with pre-enrichment and 3 without pre-enrichment by cultivation Rambach agar. Eight % of 105 pooled egg samples were positive, of which 2 were detected only from contents and 3 only from shells indicating both oviductal and faecal contamination routes of eggs. The results support the use of the extended sampling procedure in poultry flocks suspected of human food-borne Salmonella outbreaks of invasive serotypes, including not only faecal but also environmental, organ, blood and/or egg samples.