Resistance to fecal shedding of salmonellae in pigs and chickens vaccinated with an aromatic-dependent mutant of Salmonella typhimurium.

The purpose of this study was to evaluate the effectiveness of an aromatic-dependent mutant of Salmonella typhimurium as a parenteral vaccine for prevention of fecal shedding of Salmonella spp. Pigs and chickens were vaccinated IM, with 1 x 10(9) and 1 x 10(8) organisms, respectively, followed by a second identical vaccination 2 weeks later. Salmonella organisms were not detected by analysis of fecal or cloacal swab specimens from any animal after vaccination. Deleterious side effects were not noticed after vaccination. Pigs were challenge-inoculated PO with 1 x 10(12) virulent S typhimurium 1 week after the second vaccination. Chickens were challenge-inoculated PO with 3 x 10(8) organisms of either S enteritidis or the virulent parent strain of S typhimurium 3 weeks after the second vaccination. Vaccinated pigs shed Salmonella spp significantly less frequently than did nonvaccinated pigs. Vaccinated chickens challenge-inoculated with either S enteritidis or S typhimurium also shed Salmonella less frequently than the corresponding nonvaccinated control birds; however, the difference was not significant.     

Comparison of real-time PCR with conventional PCR and culture to assess the efficacy of a live attenuated Salmonella enterica serovar Typhimurium vaccine against Salmonella enterica serovar Enteritidis in commercial leghorn chicks vaccinated under field and laboratory conditions

The efficacy of a live attenuated Salmonella Typhimurium Megan Vac 1 vaccine (MV1) was evaluated against Salmonella Enteritidis in chicken pullets with the use of PCR and culture methods. Two hundred Hyline W-32 white leghorn chicks were obtained from a local hatchery and divided into four treatment groups. Two of the groups served as positive and negative controls. The MV1 vaccine was administered to the chicks in the remaining two groups at 1 and 35 days old by either the coarse spray (field) or the oral route (laboratory) method. The chicks were challenged with a high dose of a Salmonella Enteritidis strain at 10 wk old and euthanatized 3 days postinoculation. Samples for PCR analysis were collected prior to enrichment, after pre-enrichment in buffered peptone water (BPW) and after primary enrichment from the ceca, liver, and spleen. None of the samples tested yielded positive results for the Salmonella Typhimurium vaccine strain by either the culture or PCR methods. Results from the standard culture method showed that vaccinating the birds with MV1 reduced the counts of Salmonella Enteritidis recovered from the challenged birds. In addition, fewer pre-enriched samples tested positive for Salmonella Enteritidis among the challenged groups that were vaccinated when compared to the unvaccinated challenged group. Under the conditions of this study, MV1 was unable to prevent colonization of other internal organs such as the liver and spleen. Real-time PCR was significantly more sensitive than conventional PCR (C-PCR) prior to enrichment, but after enrichment the sensitivities of the two methods were similar. Enrichment significantly increased the sensitivity of both PCR methods for the detection of Salmonella Enteritidis in cecal samples, but did not significantly increase the sensitivity for detection of Salmonella Enteritidis in liver and spleen samples that were pre-enriched in BPW. There was no significant difference between the laboratory or field vaccination methods with respect to either the prevalence of Salmonella Enteritidis isolation or the bacterial loads in culture-positive samples. Collectively, the data suggest that MV1 offered some protection against Salmonella Enteritidis in commercial layer chick pullets under the conditions of this study. Given the labor and time required to perform the C-PCR and culture methods, the real-time PCR method may prove to be a more useful method to use in diagnostics.     

Effects of rearing conditions on the colonization of Salmonella enteritidis in the cecum of chicks.

Salmonella enteritidis is the cause of human salmonellosis associated with contaminated eggs. In this study, we artificially challenged S. enteritidis to chicks just after hatching, and the effects of breeding conditions on the intestinal carriage of S. enteritidis were examined. S. enteritidis was not directly detected from spleen, liver and blood, but were constantly isolated from the cecal contents throughout the experiment. When chicks were reared in the unsanitary conditions and in the high housing density, the numbers of S. enteritidis increased. The subsequent experiment was undertaken to examine whether the antibacterial additive in a feed would have any impact on S. enteritidis colonization in chicks. Some antibiotic effective on the growth promotion had an influence on S. enteritidis colonization.     

Immunization of calves with live and inactivated whole-cell vaccines against Salmonella typhimurium infection

Eight calves were immunized with live auxotrophic Salmonella typhimurium mutants (aro -SL 1479, gal E 3821) and twelve calves with phenol-killed whole-cell S. typhimurium vaccine, respectively. The clinical status of the animals was followed and serial reisolation of vaccine and challenge strains from faeces was attempted. The immunization of calves with the live aro- auxotrophic S. typhimurium SL 1479 mutant proved to be unsuitable due to the death of calves after revaccination. The calves immunized with live auxotrophic gal E S. typhimurium CCM 3821 mutant proved to be protected against challenge with virulent S. typhimurium 4/5 strain administered orally at a dose of 10(6) colony forming units (CFU). The postvaccination complications showed serious shortcomings. The immunization of calves with three doses of whole-cell inactivated vaccine containing 5 strains of S. typhimurium was effective against oral challenge with virulent S. typhimurium 4/5 at a dose of 10(6) CFU.     

Gamma/delta T cell response of chickens after oral administration of attenuated and non-attenuated Salmonella typhimurium strains

Poultry represents an important source of Salmonella infection in man. Despite intensive research on immunity, little is known about the involvement of T cell sub-populations in the immunological response of chickens against infection with non-host-adapted Salmonella (S.) serovars. In this study, the T cell composition of blood lymphocytes (CD4(+)CD8(+); CD4(+)CD8(-); CD4(-)CD8(+); CD8(+)TcR1(+); CD8(-)TcR1(+), CD8(+)TcR1(-)) after oral administration of the non-attenuated S. typhimurium wild-type strain 421 (infection) or the attenuated vaccine strain Salmonella vac((R)) T (immunization) to day-old chicks was investigated and compared with non-treated chickens by flow cytofluorometry. Additionally, the occurrence of T cell sub-populations (CD4(+); CD8(+); TcR1(+)(gammadelta); TcR2(+)(alphabeta(1))) in ceca, spleen and bursa of Fabricius of the birds was studied immunohistologically. Blood samples and tissues were examined between days 1 and 12 of age.Chicks inoculated with S. typhimurium 421 or Salmonella vac((R)) T showed significantly elevated percentages of CD8(+)TcR1(+) in blood on days 7, 8 and 9, or on day 8 in comparison to control animals. The CD4 to CD8 cell ratio was about 3:1 in infected animals on day 5 of age. In the organs of treated chicks the numbers of CD8(+)(gammadelta) and TcR1(+)(gammadelta) cells had markedly increased on days 4 and 5 in ceca, 8 and 9 in the bursa and 9 and 12 in the spleen. Moreover, infected or vaccinated birds revealed larger quantities of CD4(+) and TcR2(+) T cells in ceca on days 4 and 5. As shown by double staining, the TcR1(+) cells in the organs of infected animals additionally carried the CD8 antigen.In conclusion, immunization of day-old chicks with the attenuated Salmonella live vaccine strain resulted in the same changes in T cell composition as seen after infection with the non-attenuated Salmonella wild-type strain, but at a lower level. The remarkable increase of CD8(+)TcR1(+)(gammadelta) double positive cells in treated birds indicates an important role of this cell sub-population in the immunological defense of chickens against Salmonella exposure.     

减毒鸡沙门菌疫苗株97A的免疫保护效力试验

减毒沙门菌疫苗株97A免疫鸡经鸡沙门菌强毒株Sg9攻击后,对免疫攻毒组和攻毒对照组鸡进行病理学检查和细菌分离,以进一步评价97A疫苗的免疫保护效力。结果表明,免疫攻毒组鸡肝脏、肺脏和肾脏等实质器官仅有轻到中度的炎症反应,而攻毒对照组鸡则表现出了严重的组织病理学变化,同时减毒鸡沙门菌疫苗株97A能显著地限制强毒株在鸡体内的定居和增殖,显示出了良好的免疫保护效力。     

Comparison of different attenuation strategies in development of a Salmonella hadar vaccine

The purpose of this work was to develop a live, attenuated vaccine strain to protect chickens against colonization by group C Salmonella. We constructed two candidate vaccines: a deltacya deltacrp derivative and a deltaphoP derivative of Salmonella hadar. White Leghorn chickens were vaccinated at day of age and at 2 wk with one of the two strains. A nonvaccinated group served as a control. At 4 wk of age, all birds were challenged with wild-type S. hadar and necropsied 6 days later. Numbers of S. hadar in the ceca were determined. Enzyme-linked immunosorbent assay-derived serum immunoglobulin G responses against S. hadar lipopolysaccharide indicated that both strains induced a serum antibody response. The average optical density450 for birds vaccinated with the deltaphoP or deltacya deltacrp derivatives was 0.456 and 0.881, respectively. Although the deltacya deltacrp derivative induced higher levels of serum antibody, it did not provide an immune response protective against colonization by S. hadar. Conversely, birds vaccinated with the deltaphoP strain showed significant protection against S. hadar challenge. Seventy percent of the nonvaccinates, 60% of the deltacya deltacrp vaccinates, and 15% of deltaphoP vaccinates were positive for S. hadar in tissues. In a second experiment, birds were vaccinated with either the deltaphoP strain or buffer and challenged with a 10-fold higher dose than in the first experiment. After challenge, all of the birds in both groups were colonized. The geometric mean number of cecal S. hadar isolated from the control group was 1.0 x 10(6) colony-forming units (CFU)/g, and from the vaccinated group, this value was 32 CFU/g, indicating a four to five log reduction in colonization by the challenge strain.     

Combination of competitive exclusion and immunization with an attenuated live Salmonella vaccine strain in chickens

To use the advantages of both the competitive exclusion (CE) technique and immunization with a live Salmonella vaccine, the combination of these methods was studied. Specific-pathogen-free chickens were pretreated by combined or single administration of a CE culture and a commercial live Salmonella typhimurium vaccine on days 1 and 2 of life and challenged with Salmonella typhimurium on day 3 to study the exclusion effect by both the CE preparation and the Salmonella vaccine. The exclusion effect by the CE culture combined with the immunologic effect by the live vaccine was studied after challenge of the birds on day 43 of age. The number of challenge organisms in ceca was used to evaluate the efficacy of the pretreatment. The protective exclusion effect of the CE culture was substantial in very young chicks and still detectable in 6-wk-old birds. The attenuated Salmonella typhimurium vaccine produced only an initially occurring exclusion effect. Because the exclusion effect of the CE culture was considerably stronger than the exclusion effect of the attenuated Salmonella typhimurium vaccine, the combination of both did not result in an additive protective effect. In order to exploit the exclusion potential between Salmonella strains and to attain an additive exclusion effect by a CE culture and a vaccine strain, live Salmonella vaccines are needed that are sufficiently attenuated without affecting genes essential for colonization exclusion of other Salmonella organisms. In 6-wk-old birds, the exclusion effect by the CE culture combined with the immunologic effect by the live Salmonella vaccine resulted in a degree of protection considerably beyond that generated by the exclusive use of the two methods. The administration of the live Salmonella vaccine strain prior to or simultaneously with the CE culture revealed the best protective effect because such combinations ensure an adequate persistence of the vaccine strain as prerequisite for the expression of an exclusion effect in very young chicks and the development of a strong immune response affording protection in older birds.     

鸡沙门氏菌弱毒株的效力和安全试验

将鸡沙门氏菌弱毒株以不同剂量分别经口服和颈部皮下接种1日龄商品蛋鸡进行安全性和免疫效力研究,结果表明：该弱毒株对1日龄雏鸡有良好的安全性并能提供较强的保护力。     

Pathologic and bacteriologic findings in 27-week-old commercial laying hens experimentally infected with Salmonella enteritidis, phage type 4

Two strains of 27-wk-old commercial laying chickens (strain A, brown-egg-laying type and strain B, white-egg-laying type) were inoculated either orally (PO) or intravenously (IV) with a field isolate of Salmonella enteritidis phage type 4. Chickens were sequentially necropsied at regular intervals throughout the 17-wk observation period. Gross and microscopic lesions were most evident between 1 and 14 days postinoculation (DPI). Gross lesions consisted of enlarged livers with white foci, enlarged and mottled white spleens, fibrinous exudate in the peritoneum, and atretic, misshapen ovarian follicles. Microscopic lesions included multifocal coagulative necrosis of hepatocytes and inflammation, fibrinous exudation in vascular sinuses of the spleen, and fibrinosuppurative inflammation of the peritoneum and ovarian follicles. The proportion of reproductive organ infections (ovary and oviduct) in the IV group, 83% (20/24, P = 0.007; 50% and 33% for strains A and strain B birds, respectively), was higher than that of the PO group, 46% (11/24; 29% and 17% for strains A and B, respectively), for the first 16 days of observation postinoculation. The proportion of fecal shedding for the IV group of birds was significantly (P = 0.009) lower, 29% (7/24; 33% and 25% respectively for strain A and strain B birds, respectively), than the PO group, 67% (16/24; 75% and 58% for strain A and strain B birds, respectively). Three (2.6%) of 234 egg pools were culture-positive for group D Salmonella from strain A chickens (1 of 119 pools from the IV group and 2 of 115 pools from the PO group of birds). Chickens infected with the field strain of S. enteritidis phage type 4 harbored the organism in tissues only for a brief time, most clearing within 8 DPI and nearly all within 16 DPI. Overall the percentage of culture-positive birds did not differ significantly (P > 0.05) between birds with and without lesions, but isolation of S. enteritidis tended to be more frequent when lesions were evident. This experiment also demonstrated that brown-egg-laying-type chickens were more susceptible than white-egg-laying-type chickens to S. enteritidis phage type 4 isolated from California based on gross and microscopic lesions and bacteriologic findings.     

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

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

A Salmonella abortusovis inactivated vaccine protects mice from abortion after challenge.

Two types of Salmonella abortusovis vaccines were prepared, one with aluminium hydroxide (vaccine A) and the other with water in oil (vaccine B) adjuvants. They were compared in a pregnant mouse model, aiming at protecting them from abortions after challenge with a virulent strain of S. abortusovis. The protection for vaccine A was from 74% to 77.6% and that for vaccine B from 71% to 79.6%. Abortions occurred 5-10 days post challenge and S. abortusovis was isolated from all aborted fetuses and from the liver and the spleen of their mothers at the end of the experiment (18 days post challenge). The presence of salmonella in the liver and the spleen of vaccinated non-pregnant but challenged mice was studied in a separate experiment. The bacterium was isolated from one out of 12 vaccinated mice 6 days post challenge as well as from the six controls.     

Generation of aromatic-dependent Salmonella havana and evaluation of its immunogenic potential in mice and sheep.

The generation of aromatic-dependent (aro-) Salmonella havana (Group G2, 01, 13, 23) from a smooth wild-type parent strain by transduction with phage P1 is reported. Mice immunized with this live aro- S. havana strain (CS234) by the intraperitoneal (i.p.) route were protected against challenge with wild-type S. havana, whereas those immunized by the oral route were not. Mice immunized with two doses of formalin-killed aro- S. havana by the i.p. route were also unprotected, in spite of high antibody titers. However, only those mice immunized with live aro- S. havana by the i.p. route developed significant delayed-type hypersensitivity. Following i.p. inoculation in mice, the aro- S. havana strain CS234 was detected in the liver, spleen and mesenteric lymph nodes on day 9 but not on day 15 post-inoculation (p.i.). On the other hand, when mice were inoculated with the parent wild-type strain (CS4) or the aro- derivative strain CS234 by the oral route, the organisms were recovered from the mesenteric lymph nodes and intestine only on day 3 but not on day 6 post-inoculation. In sheep inoculated with the aro- strain CS234 in the gastroc muscle, organisms were recovered from the muscle, and popliteal and medial iliac lymph nodes for up to 21 but not 28 days p.i. However, no mutant organisms were recovered from liver, spleen, mesenteric lymph nodes or faeces. In orally-inoculated sheep, the mutant organisms were recovered from the mesenteric lymph nodes, rumen, intestinal contents, and faeces up to 14-21 days post-inoculation but not at 28 days. When sheep immunised with the aro- S. havana strain CS234 by the intramuscular or oral route were challenged with the parent wild-type S. havana strain CS4 by the oral route, the latter strain was detectable in the mesenteric lymph nodes and faeces of immune sheep up to 14 days post-challenge in contrast with the non-immune sheep, where the challenge strain was detectable even at 28 days post-challenge. Only sheep immunized by the intramuscular route developed high antibody levels and delayed-type hypersensitivity.     

Cross-protection against Salmonella Typhimurium infection conferred by a live attenuated Salmonella Enteritidis vaccine

In this study, a genetically engineered live attenuated Salmonella Enteritidis (SE) vaccine was evaluated for its ability to protect against Salmonella Typhimurium (ST) infection in chickens. The birds were orally primed with the vaccine on the 1st day of life and given an oral booster at 5 wk of age. Control birds were orally inoculated with phosphate-buffered saline. Both groups of birds were orally challenged with a virulent ST strain at 9 wk of age. Compared with the control chickens, the vaccinated chickens had significantly higher levels of systemic IgG and mucosal IgA against specific ST antigens and a significantly greater lymphoproliferative response to ST antigens. The excretion of ST into the feces was significantly lower in the vaccinated group than in the control group on days 9 and 13 d after challenge. In addition, the vaccinated group had significantly fewer pronounced gross lesions in the liver and spleen and lower bacterial counts in the internal organs than the control group after challenge. These data indicate that genetically engineered live attenuated SE may induce humoral and cellular immune responses against ST antigens and may confer protection against virulent ST challenge.     

Decreased colonization of chicks by Salmonella enterica serovar Gallinarum expressing mannose-sensitive FimH adhesin from Salmonella enterica serovar Enteritidis

To investigate the role of non-hemagglutinating type 1 fimbriae in the pathogenesis of Salmonella Gallinarum, the isogenic mutant elaborating type 1 fimbriae with mannose-sensitive (MS) variant of the FimH adhesin from Salmonella Enteritidis and the mutant strain with no FimH expression were constructed. Their binding to chicken leukocytes in vitro and invasiveness in 1-day-old chicks were studied. Our results demonstrated that S. Gallinarum type 1 fimbriae with an endogenous variant of the FimH adhesin mediated mannose-resistant (MR) binding to avian leukocytes and did not bind to human epithelial cells. However, after allelic replacement of the FimH, mutated fimbriae with S. Enteritidis variant of the FimH adhesin bound to both cell types in a mannose-dependent manner. In chick model, S. Gallinarum expressing wild-type FimH variant colonized cecal tonsils and bursa of Fabricius more effectively and invaded the spleen and liver in greater numbers than S. Gallinarum fimH knockout strain or mutant expressing MS FimH variant from S. Enteritidis. The invasive potential of the latter was greatly reduced in chicks since no viable bacteria expressing MS variant of the adhesin could be recovered from intestinal lymphoid tissues or liver over a 6 days course of infection. Together, these results demonstrate that the S. Gallinarum type 1 fimbriae with the endogenous MR variant of the FimH protein increase systemic dissemination of S. Gallinarum and colonization of internal organs in chicks indicating the importance of these adhesive structures in the virulence of S. Gallinarum.     

Adjuvanted Outer Membrane Protein Vaccine Protects Poultry against Infection with Salmonella enteritidis

The immunogenicity of a sonicated extract (SE) and of outer membrane proteins (OMP) of Salmonella enteritidis was tested in birds of about 8 weeks of age. The dose, route of vaccination and the adjuvant used varied in different groups of birds. Two vaccine doses with or without adjuvant were given parenterally or orally 3 weeks apart. OMP vaccines gave significantly higher antibody titres than SE vaccines, as indicated by ELISA. The vaccines adjuvanted with oil produced higher antibody titres than those without any adjuvant. A dose of 1 mg of vaccine produced higher antibody titres than 0.5 mg of vaccine. Adjuvanted vaccine given subcutaneously elicited higher antibody responses than oral vaccines given without adjuvant. The birds were challenged with virulent S. enteritidis organisms at the end of the second week after a booster dose. None of the birds given 1 mg of OMP vaccine subcutaneously shed the organisms when tested by culturing cloacal swabs, although a few birds vaccinated with 0.5 mg of OMP vaccine did so. In general, adjuvanted OMP vaccines gave better protection than SE vaccines.     

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.     

Use of a live attenuated Salmonella typhimurium vaccine to protect hens against Salmonella enteritidis infection while undergoing molt

Previous studies demonstrated that Salmonella enteritidis infections in hens undergoing molt via feed withdrawal were more severe than in full fed hens. We conducted two trials to determine if immunizing specific-pathogen-free, Salmonella-culture-negative hens via aerosol exposure to MeganVacl, a commercially available attenuated Salmonella typhimurium vaccine, would reduce transmission of S. enteritidis from infected hens to uninfected but contact-exposed hens during a molt. In trial 1, one group of hens received two aerosol doses of vaccine 2 wk apart whereas a second group of hens remained nonvaccinated. In trial 2, the vaccinated group received only one dose of vaccine. Two weeks after the final immunization, feed was removed from all the hens, and on day 4, the center hen in rows of 11 hens received a dose of 3 x 10(5) (trial 1) or 1.3 x 10(6) (trial 2). Transmission to the unchallenged hens was followed 3, 10, 17, and 24 days later. Vaccination reduced the horizontal spread of S. enteritidis in vaccinated hens compared with their nonvaccinated counterparts, with vaccinated hens shedding significantly less S. enteritidis on day 10 postchallenge in trial 1 and on days 3, 10, 17, and 24 in trial 2. Recovery of S. enteritidis from ovaries was significantly reduced in the vaccinated hens in trial 1 and from livers/spleens, ovaries, and cecum in trial 2. These studies indicate that immunization of hens with a live S. typhimurium vaccine could help reduce S. enteritidis problems during a molt situation.     

Cell-mediated and humoral immune responses to a virulent plasmid-cured mutant strain of Salmonella enterica serotype gallinarum in broiler chickens

One-week-old Salmonella-free broiler chicks were subcutaneously immunized and subsequently boosted two weeks later with 2x10(7)cfu 0.5ml(-1) of an 85-kb virulent plasmid-cured spectinomycin-resistant mutant strain (SG9VP(-)Spc(r)) of Salmonella gallinarum 9 (S. enterica serotype gallinarum 9) along with a control group of mock-immunized chickens. The chicks were subcutaneously challenged at 5 weeks of age with 5x10(10)cfu 0.5ml(-1) (5xLD(50)) of wild-type S. gallinarum var. Duisburg (S. enterica serotype gallinarum var. Duisburg). The cellular and humoral immune responses were measured at weekly intervals post-immunization (PI) and post-challenge (PC) using lymphocyte stimulation test (LST), delayed type hypersensitivity (DTH) test, serum tube agglutination test (STAT) and enzyme-linked immunosorbent assay (ELISA). High stimulation indices suggestive of a potent lymphocyte transformation response and high persistent serum IgG titres were recorded in immunized chickens at the termination of the experiment. These findings indicate that the live attenuated mutant vaccine induced a strong cellular and humoral immunity, which may play a role in the protection of fowl typhoid in broiler chickens.     

Efficacy for a New Live Attenuated Salmonella Enteritidis Vaccine Candidate to Reduce Internal Egg Contamination

To evaluate the efficacy of a novel attenuated Salmonella Enteritidis (△lon△cpxR) vaccine candidate (JOL919), chickens were immunized through oral and intramuscular routes to reduce egg contamination against S. Enteritidis challenge. Birds were orally immunized with JOL919 on the first day of life and were subsequently boosted in the 6th and 16th weeks through oral (group B) or intramuscular (group C) route, while control birds were unimmunized (group A). The chickens of all groups were challenged intravenously with the virulent S. Enteritidis strain in the 24th week. The immunized groups B and C showed significantly higher plasma IgG and intestinal secretory IgA levels as compared to those of the control group. The lymphocyte proliferation response and CD45⁺CD3⁺ T‐cell number in the peripheral blood of the groups B and C were significantly increased. In addition, the egg contamination rates were significantly lower in the group B (0%, 10.7% and 0%) and the group C (3.6%, 14.3% and 3.6%) as compared to the group A (28.6%, 42.8% and 28.6%) in the 1st, 2nd and 3rd weeks post‐challenge. All animals in the groups B and C showed lower organ lesion scores in the liver and spleen and lower bacterial counts in the liver, spleen and ovary at the 3rd week post‐challenge. These results indicate that this vaccine candidate can be an efficient tool for prevention of Salmonella infections by inducing protective humoral and cellular immune responses. In addition, this vaccine did not prevent egg contamination, but did appear to reduce incidence. Booster immunizations, especially via oral administration route, showed an efficient protection against internal egg contamination with S. Enteritidis.