Vaccination of calves with orally administered aromatic-dependent Salmonella dublin

Bradford Phillips Smith From the Department of Medicine, School of Veterinary Medicine, University of California, Davis, CA 95616 (Smith, Dilling, Roden) and the Department of Medical Microbiology, School of Medicine, Stanford University, Stanford, CA 94305 (Stocker).

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George Wayne Dilling From the Department of Medicine, School of Veterinary Medicine, University of California, Davis, CA 95616 (Smith, Dilling, Roden) and the Department of Medical Microbiology, School of Medicine, Stanford University, Stanford, CA 94305 (Stocker).

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Lin Da Roden From the Department of Medicine, School of Veterinary Medicine, University of California, Davis, CA 95616 (Smith, Dilling, Roden) and the Department of Medical Microbiology, School of Medicine, Stanford University, Stanford, CA 94305 (Stocker).

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Bruce A. D. Stocker From the Department of Medicine, School of Veterinary Medicine, University of California, Davis, CA 95616 (Smith, Dilling, Roden) and the Department of Medical Microbiology, School of Medicine, Stanford University, Stanford, CA 94305 (Stocker).

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Summary

Genetically altered stable nonreverting aromatic-dependent (aro-) Salmonella dublin, strain SL5631, was administered orally to healthy colostrum-fed calves as vaccine. Twenty-six calves were allotted to 4 groups. There were 2 experiments, each with a vaccinated and nonvaccinated control group. Skin testing with 0.1 ml of sonicated S dublin was performed 3 days prior to challenge exposure. The IgG and IgM titers to S dublin lipopolysaccharide (lps) antigen were determined by elisa on sera before initial vaccination and at 1.5 to 2 weeks after each vaccination.

In experiment 1, six calves received a dose of 1.7 × 1010 colony-forming units (cfu) of aro-S dublin SL5631 orally at 2 and 4 weeks of age. After the first vaccination, 2 of 6 calves developed fever, but all 6 calves continued to have normal appetite and mental attitude. Adverse changes were not observed after the second vaccination. At the time of challenge exposure at 6 weeks of age, all 12 calves were seronegative for IgG and IgM lps-specific antibodies, and the difference in percentage increase in skin test reaction at 48 hours was not significant. At 6 weeks of age, the 6 vaccinates and 6 controls were orally challenge-exposed with 1.5 × 1011 cfu of virulent S dublin T2340. Protection from challenge was not evident, as 3 of 6 controls and 5 of 6 vaccinates died after challenge exposure.

In experiment 2, eight calves received a dose of 5 × 1011 cfu of aro-S dublin SL5631 orally at 2, 3.5, and 5 weeks of age. The vaccine dose and volume (300 ml) were 30 times that of experiment 1. After each vaccination, some calves (7, 6, and 2 calves for first, second, and third doses, respectively) developed fever, but all calves continued to have normal appetite and attitude. At 7 weeks of age, the 8 vaccinates and 6 controls were orally challenge-exposed with 1.5 × 1011 cfu of virulent S dublin T2340 (same dose as experiment 1). At the time of challenge exposure, all 8 vaccinated calves had elisa titers to IgG and IgM lps-specific antibodies significantly above those of nonvaccinated calves (P < 0.01 and P < 0.05, respectively), 5 of 8 had a strongly posisitive skin test reaction to lps, and the group mean percentage increase in skin thickness 48 hours after intradermal injection was 135% (P = 0.01). The 6 control calves had negative elisa results and mean increase in skin thickness of 34%. Protection from challenge exposure was evident as vaccinates remained blood culture-negative, whereas 5 of 6 controls were blood culture-positive; vaccinates did not develop diarrhea, whereas all controls developed diarrhea. All vaccinates survived, but 3 of 6 controls died after challenge exposure (P = 0.05).

Failure of orally administered vaccine to protect calves in experiment 1 appeared attributable to insufficient antigenic stimulation when 1.7 × 1010 cfu of aroS dublin SL5631 was administered. In experiment 2, a larger number of vaccinal organisms given orally was able to induce a measurable systemic immune response and protection, but the vaccine volume makes it unlikely to be practical for field use.

Summary

Genetically altered stable nonreverting aromatic-dependent (aro-) Salmonella dublin, strain SL5631, was administered orally to healthy colostrum-fed calves as vaccine. Twenty-six calves were allotted to 4 groups. There were 2 experiments, each with a vaccinated and nonvaccinated control group. Skin testing with 0.1 ml of sonicated S dublin was performed 3 days prior to challenge exposure. The IgG and IgM titers to S dublin lipopolysaccharide (lps) antigen were determined by elisa on sera before initial vaccination and at 1.5 to 2 weeks after each vaccination.

In experiment 1, six calves received a dose of 1.7 × 1010 colony-forming units (cfu) of aro-S dublin SL5631 orally at 2 and 4 weeks of age. After the first vaccination, 2 of 6 calves developed fever, but all 6 calves continued to have normal appetite and mental attitude. Adverse changes were not observed after the second vaccination. At the time of challenge exposure at 6 weeks of age, all 12 calves were seronegative for IgG and IgM lps-specific antibodies, and the difference in percentage increase in skin test reaction at 48 hours was not significant. At 6 weeks of age, the 6 vaccinates and 6 controls were orally challenge-exposed with 1.5 × 1011 cfu of virulent S dublin T2340. Protection from challenge was not evident, as 3 of 6 controls and 5 of 6 vaccinates died after challenge exposure.

In experiment 2, eight calves received a dose of 5 × 1011 cfu of aro-S dublin SL5631 orally at 2, 3.5, and 5 weeks of age. The vaccine dose and volume (300 ml) were 30 times that of experiment 1. After each vaccination, some calves (7, 6, and 2 calves for first, second, and third doses, respectively) developed fever, but all calves continued to have normal appetite and attitude. At 7 weeks of age, the 8 vaccinates and 6 controls were orally challenge-exposed with 1.5 × 1011 cfu of virulent S dublin T2340 (same dose as experiment 1). At the time of challenge exposure, all 8 vaccinated calves had elisa titers to IgG and IgM lps-specific antibodies significantly above those of nonvaccinated calves (P < 0.01 and P < 0.05, respectively), 5 of 8 had a strongly posisitive skin test reaction to lps, and the group mean percentage increase in skin thickness 48 hours after intradermal injection was 135% (P = 0.01). The 6 control calves had negative elisa results and mean increase in skin thickness of 34%. Protection from challenge exposure was evident as vaccinates remained blood culture-negative, whereas 5 of 6 controls were blood culture-positive; vaccinates did not develop diarrhea, whereas all controls developed diarrhea. All vaccinates survived, but 3 of 6 controls died after challenge exposure (P = 0.05).

Failure of orally administered vaccine to protect calves in experiment 1 appeared attributable to insufficient antigenic stimulation when 1.7 × 1010 cfu of aroS dublin SL5631 was administered. In experiment 2, a larger number of vaccinal organisms given orally was able to induce a measurable systemic immune response and protection, but the vaccine volume makes it unlikely to be practical for field use.

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