Groninga-vetx article (1,1)

K. J. Groninga, E. Springer, M. Braunschmidt, and D. Pankratz Salmonella derby Cross-Protection Study*
Kenneth J. Groninga, DVMa
Eric Springer, BSb
Matthew Braunschmidt, BSb
Duane Pankratz, DVM, MSc
aSwine Health ConsultantGrand Laboratories, Inc. bGrand Laboratories, Inc.
1447 140th St.
Larchwood, IA 51241 ■ ABSTRACT
1998. Salmonella spp. were chosen to be indi- An avirulent live (AVL), Salmonella cholerae- cator pathogens because they are the most suis vaccine (Salmo Shield Live® [Grand Labo- common bacterial cause of food-borne illness.3 ratories, Inc.]) was administered to pigs at An effort is underway to gather information on weaning or 3 weeks of age. Two weeks after reducing and controlling Salmonella at the vaccination the vaccinated pigs as well as un- farm level.2 Most epidemiologic research on vaccinated control pigs were challenged in- Salmonella in the United States has been fo- tranasally with a commonly isolated environ- cused on disease prevention and control in mental Salmonella serotype, S. derby. At 2, 4, and 6 weeks after challenge, pigs were eutha- asymptomatic, zoonotic Salmonella spp. has nized and cultured for S. derby. Although the been very limited.4 Minnesota research has in- number of pigs in this study was too small to dicated that environmental Salmonella draw any definite generalizable conclusions, serotypes isolated at the nursery stage of pro- the vaccinated pigs had significantly reduced duction have better correlation with serotypes reisolation rates of S. derby when compared isolated at slaughter than those serotypes iso- with the control pigs. Further research in this lated at the finisher stage of production.4 A similar study done by J.R. Kolb et al.5 usinganother commercially available avirulent live ■ INTRODUCTION
(AVL), S. choleraesuis vaccine indicated that the prevalence of Salmonella spp. at slaughter major concerns for swine practitioners and could be reduced by the use of such a vaccine.
pork producers alike.1,2 Major packing plants adopted the Hazard Analysis Critical Control nursery-age pigs at the farm level to determine if an AVL, S. choleraesuis vaccine (Salmo Shield *This study was sponsored by Grand Laboratories, Inc.
Live® [Grand Laboratories, Inc.]) could be Veterinary Therapeutics • Vol. 1, No. 1, Winter 2000 Two weeks after vaccination all pigs were TABLE 1. Necropsy Schedule
challenged intranasally with an S. derby culture prepared in NorBroth® media. All pigs re-ceived 1.0 ml per nostril of the prepared chal- lenge culture. Viability of the challenge culture was determined to be 2.04 × 1010 CFU/mL for a total of 4.1 × 1010 CFU/challenge dose. At 2,4, and 6 weeks after challenge, pigs were used as a tool to reduce reisolation rates of S. necropsied and cultured for the challenge iso- derby in vaccinated versus control pigs that had late. A serology test such as the Mix-ELISA test been challenged intranasally with a live culture could have been used to indicate the preva- lence of many Salmonella spp., but in thisstudy culture was used because the challenge ■ MATERIALS AND METHODS
isolate was the only organism of concern. This Subjects
study was terminated 6 weeks after challenge The pigs used in this study were farrowed due to the limited number of pigs in the study.
from 16 gilts that were selected from a 125- Table 1 shows the necropsy schedule.
sow commercial herd. This herd was selectedbecause it was determined to be free of any Necropsy Tissue Re-isolation
Salmonella infection; the authors did not want At 2 weeks after challenge, designated pigs the pigs to have natural immunity to any Sal- were euthanized and cultured for S. derby. Tis- monella spp. because this may have interfered sues cultured were lung, liver, spleen, tonsil, with the study results. Therefore the vaccine colon, ileocecal junction, ileocecal lymph and challenge Salmonella organisms used in nodes, and mesenteric lymph nodes. Fecal cul- this study were the first and only Salmonella tures were not used because the object of this organisms to which these pigs were exposed.
study was to determine the prevalence of thechallenge isolate in swine tissues as an indicator Procedure
of pork quality. The presence of the challenge isolate in feces would not be a reliable indicator were weaned at 3 weeks of age and grouped of pork quality. Tissues were inoculated onto into one pen. The 24 weaned pigs were then blood agar, XLT4, and S. shigella agar plates.
individually and randomly assigned to either The plates were incubated at 37˚C overnight.
an intramuscular vaccinate (IM) or nonvacci- Tissues were also inoculated into 10 ml of Rap- nate control group. Each group was housed in paport-Vassiliadis (RV) enrichment media. The the same barn in separate pens. The pigs in the RV enrichment media was incubated at 42˚C overnight. Following incubation the RV enrich- weeks of age according to label directions on the vaccine. The resulting groups were as fol- XLT4, and S. shigella agar plates. The plates were incubated at 37˚C overnight. Suspect S.
derby colonies (as determined by colony mor- phology) from both the direct culture and RV enriched cultures were plated for purity for identity testing. Pure suspect cultures were K. J. Groninga, E. Springer, M. Braunschmidt, and D. Pankratz TABLE 2. Summarization of S. derby Reisolation Results
VACC = vaccinated intramuscularly with 1 mL (in neck).
CONTROL = nonvaccinated.
Salmonella Positive = determined by biochemical tests (TSI, MIO, and Tergitol 7).
identified as Salmonella by their reaction on in Table 2. Fisher’s exact test demonstrated sig- triple sugar iron (TSI); motility, indol, or- nificant differences in re-isolation at 4 weeks nithine (MIO); and Tergitol 7 media. The vac- (P = 0.0143) and for the entire study (P = cine and challenge strains were differentiated by their sensitivity to tetracycline. At 4 and 6weeks after challenge, the remaining designated ■ DISCUSSION
pigs were euthanized and only the ileocecal The AVL, S. choleraesuis vaccine (Salmo junction and ileocecal lymph nodes were cul- Shield Live® [Grand Laboratories, Inc.]) was tured as described above. Individual re-isolation shown to be efficacious in this study in cross- results for each pig and tissue are on file.
protecting vaccinated animals against chal-lenge with S. derby, an environmental Salmo- ■ ANALYSIS
nella serotype, up to 6 weeks after vaccination.
S. derby re-isolation results are summarized Because of the limited number of pigs in this Veterinary Therapeutics • Vol. 1, No. 1, Winter 2000 study, a larger scale study should be done, per- la isolation rates can be significantly reduced haps using Salmonella typhimurium as the chal- at slaughter in vaccinated versus nonvaccinat- lenge isolate with the final re-isolation attempt ■ REFERENCES
■ CONCLUSION
1. Dufresne L: Alimentary Tract Disorders of Growing Pigs, The exact mechanism of this cross-protec- Proceedings-International Pig Veterinary Society 1:71–77,1998.
tion against a heterologous Salmonella 2. Damman DJ, Bahnson P, Isaacson PB, Kim JY: Evalu- serotype is unknown, but the opinion of the ation of Salmonella spp. Prevalence on Illinois, USA, authors is that it is a function of the cell-me- Swine Farms, Proceedings—International Pig Veterinary diated immune system rather than the anti- 3. Federal Register: Pathogen Reduction Performance Stan- dards 63(63):16243–16245, 1998.
of this study indicate that an AVL, S. choler- 4. Carlson AR, Blaha T: On farm Salmonella control pro- aesuis vaccine such as Salmo Shield Live® cedures—what is known? Proceedings—Iowa State Uni- (Grand Laboratories, Inc.) may be a viable versity-swine disease conference for swine practitioners tool to use in reducing the isolation rate of environmental Salmonella serotypes at slaugh- 5. Kolb JR, Roof MB, Burkart K: Reduction of Salmonel- la species contamination of swine carcasses utilizing ter. However, a larger scale study must be vaccination with an avirulent live Salmonella cholerae- done in a commercial, Salmonella-infected suis vaccine (SC-54) at placement in grower/finisher.
herd in order to determine if these Salmonel- Proceedings of the 15th IPVS Congress 2:74, 1998.

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