Control of Salmonella Enteritidis and Salmonella Gallinarum in birds by using live vaccine candidate containing attenuated Salmonella Gallinarum mutant strain.

The ideal live vaccine to control Salmonella in commercial chicken flocks should engender protection against various strains. The purpose of the present study was to confirm the attenuation of a Salmonella Gallinarum (SG) mutant strain with deletion on genes cobS and cbiA, that are involved in the biosynthesis of cobalamin. Furthermore, evaluate its use as a live vaccine against Salmonella. For the evaluation of the vaccine efficacy, two experiments were conducted separately. Birds from a commercial brown line of chickens were used to perform challenge with SG wild type strain and birds from a commercial white line of chickens were used to perform challenge with Salmonella Enteritidis (SE) wild type strain. In both experiments, the birds were separated in three groups (A, B and C). Birds were orally vaccinated with the SG mutant as the following programme: group A, one dose at 5 days of age; group B, one dose at 5 days of age and a second dose at 25 days of age; and group C, birds were kept unvaccinated as controls. At 45 days of age, birds from all groups, including the control, were challenged orally by SG wild type (brown line) or SE wild type (white line). Lastly, another experiment was performed to evaluate the use of the SG mutant strain to prevent caecal colonization by SE wild type on 1-day-old broiler chicks. Mortality and systemic infection by SG wild type strain were assessed in brown chickens; faecal shedding and systemic infection by SE wild type were assessed in white chickens and caecal colonization was assessed in broiler chicks. Either vaccination with one or two doses of SG mutant, were capable to protect brown chickens against SG wild type. In the experiment with white chickens, only vaccination with two doses of SG mutant protected the birds against challenge with SE wild type. Although, SG mutant could not prevent caecal colonization in 1-day-old broiler chicks by the challenge strain SE wild type. Overall, the results indicated that SG mutant is a promising Salmonella live vaccine candidate that demonstrated good efficacy to control the infection by two serotypes of major importance to the poultry industry.

Penha Filho RA ，de Paiva JB ，da Silva MD ，de Almeida AM ，Berchieri A Jr ... -  《-》

Vaccination against Salmonella enteritidis in Dutch commercial layer flocks with a vaccine based on a live Salmonella gallinarum 9R strain: evaluation of efficacy, safety, and performance of serologic Salmonella tests.

This study describes a field trial in which 80 commercial layer flocks, with an increased risk of Salmonella enteritidis (SE) infection and placed on farms with a certified Standardized Biosecurity Programme (SBP) or a request for a SBP certificate, were vaccinated with a vaccine based on a live attenuated Salmonella gallinarum (SG) 9R strain. An evaluation is presented of the efficacy of the vaccine against SE infections, the effect on the performance of serologic Salmonella tests, and the spread of the vaccine strain to the egg content. For the efficacy study, assessment of the flock level occurrence of SE infections in the vaccinated group of 80 flocks was compared with that of a nonvaccinated group of 1854 flocks hatched in the same period. This control group was examined according to the compulsory control programme in The Netherlands. An evaluation was done of the performance of serologic Salmonella tests and the spread of the vaccine strain to the inner egg content of five of the vaccinated flocks. Findings demonstrated the flock level occurrence of SE infections in the vaccinated group (2/80 = 2.5%) to be significantly (P = 0.01) lower than that of the nonvaccinated group (214/1854 = 11.5%). Vaccination resulted in 59.0% positive test results in lipopolysaccharide BD enzyme-linked immunosorbent assay (ELISA) for detecting antibodies against Salmonella serogroups B and D and 0% positive test results in the rapid plate agglutination test for detecting antibodies against S. pullorum (SP)/SG. The mean specificities of two blocking ELISAs (gm- and i-double antibody sandwich ELISAs) based on the flagellar antigen of SE and Salmonella typhimurium (ST) on the same sera were 99.6% and 96.1%, respectively. The vaccine strain could not be isolated from any of the 450 pools of 10 eggs. On the basis of these results, we concluded that vaccination with a vaccine based on an attenuated SG 9R strain contributes to the reduction of SE infections in commercial layer flocks. Furthermore, serologic monitoring of SE, ST, and SP/SG can still be carried out on flocks vaccinated with an attenuated SG 9R strain. Additionally, we found no indication of the spread of the vaccine strain to the egg content.

Feberwee A ，de Vries TS ，Hartman EG ，de Wit JJ ，Elbers AR ，de Jong WA ... -  《AVIAN DISEASES》

The effect of oral administration of a homologous hilA mutant strain on the long-term colonization and transmission of Salmonella Enteritidis in broiler chickens.

The effect of pre-treatment with a homologous live Salmonella hilA mutant strain on the long-term colonization and transmission of Salmonella Enteritidis in broilers was evaluated. For this purpose, three treatment groups of newly hatched broilers were created. Each group consisted of 4 pens with 25 birds per pen. The first and second groups were orally inoculated with a Salmonella Enteritidis hilA mutant strain (Nal r) whereas the third group was not. In the second and third group, 20% of the birds were challenged 1 day later with a Salmonella Enteritidis wild type strain (Strep r). The Salmonella Enteritidis hilA mutant strain showed no residual virulence in the chicken host and was largely cleared from the chickens at 6 weeks of age. A significant long-term inhibition of faecal shedding and caecal and internal organ colonization of the wild type Salmonella Enteritidis strain was observed in the birds pre-treated with the hilA mutant strain. Although pre-treatment with a hilA mutant strain could not fully prevent the spread of Salmonella Enteritidis amongst the broilers, a significant reduction of transmission was observed in comparison to the non-pre-treated groups. The observed colonization-inhibition (CI) indicates that administration of live attenuated hilA mutant Salmonella strains to newly hatched chicks might, in combination with other protective control measures, contribute to the control of Salmonella infections in broilers.

Bohez L ，Dewulf J ，Ducatelle R ，Pasmans F ，Haesebrouck F ，Van Immerseel F ... -  《VACCINE》

Safety and efficacy of a metabolic drift live attenuated Salmonella Gallinarum vaccine against fowl typhoid.

Fowl typhoid (FT), a systemic disease that results in septicemia in poultry, is caused by Salmonella enterica serovar Gallinarum biovar Gallinarum (SG). Mortality and morbidity rates from FT can reach up to 80%. Attenuated live Salmonella vaccine candidates have received considerable attention because they confer solid immunity, and they can produce systemic and mucosal immunity in the gut when administered orally. In the present study, five metabolic drift (MD) mutants with a single-(designated SG-Rif1, SG-Sm6) or double-attenuating marker (designated SG-Rif1-Sm4, SG-Sm6-Rif10, and SG-Rif1-Sm10) were isolated. The relative colony sizes to wild-type strain after 24 hr at 37 C incubation were 50%, 40%, 30%, 30%, and 20%, respectively. The probability of a back mutation can almost be excluded because the reduced colony sizes were stable after at least 50 passages on culture media. The safety and immunogenicity were evaluated in susceptible 1-day-old commercial layer chickens. After oral administration of 10(8) colony-forming units (CFU), all developed MD mutants proved to be safe and did not cause death of any infected birds during 15 days postvaccination, whereas chickens receiving 10(6) CFU SG wild-type strain showed a high mortality rate (40%). Vaccination of commercial layer chicks with SG-Rif1, SG-Sm6, SG-Rif1-Sm4, and SG-Sm6-Rif10 MD mutants could protect chickens against challenge by homologous wild-type strain; however, SG-Rif1-Sm10 could not protect against challenge, indicating hyperattenuation. In conclusion, vaccination with SG MD mutant vaccine appears to be safe and offers protection against FT in chickens.

Shehata AA ，Sultan H ，Hafez HM ，Krüger M ... -  《AVIAN DISEASES》

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

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

Penha Filho RA ，de Paiva JB ，Arguello YM ，da Silva MD ，Gardin Y ，Resende F ，Berchieri Junior AB ，Sesti L ... -  《-》