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Summary
Salmonella choleraesuis strain 38 (glycerol-positive fermentation) was repeatedly exposed to porcine neutrophils in an attempt to mimic in vivo conditions of the host immune system. After phagocytosis, viable intracellular S choleraesuis were isolated and the process was repeated at least 5 times. A fifth-passage strain-38 neutrophil-adapted clone, 38PMNa-5X, was isolated, and was compared with the parent wild-type strain 38 for changes. Strain 38PMNa-5X had increased resistance to killing by hydrogen peroxide and phagocyte killing by porcine neutrophils, as measured by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction. Strain 38PMNa-5X was less invasive than the parent strain on Vero cell monolayers, and had been cured of a 50-kb plasmid. The 50-kb plasmid was marked with bacteriophage mini-Mu (kanamycin resistant) and was reinserted into strain 38PMNa-5X. Strain 38PMNa-5X was avirulent in mice, but the isolates with reinserted plasmids had intermediate resistance to neutrophil and hydrogen peroxide killing and had restored invasiveness and mouse virulence. Differences in complement sensitivity and enzymatic activity were not observed between the strains.
Summary
Seventy-five pigs from 4 facilities were examined for Salmonella choleraesuis by use of bacteriologic culture of feces, blood, wbc (buffy coat), mononuclear leukocytes, and neutrophils. The organism was isolated from 0 of 75 fecal samples, compared with isolation from 39 of 75 purified neutrophil preparations. Of the pigs that did not have Salmonella isolated from feces or blood, but had S choleraesuis isolated from neutrophils, 6 were further examined. These pigs from 2 groups again had culture performed at least 3 successive times to test for repeatability and to determine optimal number of neutrophils required for Salmonella isolation. These same pigs were euthanatized and necropsied. Nineteen tissue specimens from each pig were obtained for culture, but S choleraesuis was isolated only from neutrophil samples. Results indicate that neutrophils may contribute to the carrier state in pigs and should be cultured when attempting to identify S choleraesuis carrier swine.
SUMMARY
The growth hormone (gh) secretagogue activity of variable dosages of clonidine (16.5, 50, 150, and 450 μg/kg of body weight), given orally mixed with the daily food ration, was evaluated in young and old dogs. Significant (P < 0.05) increase in plasma gh concentration was detected at all dosages tested in young dogs and in response to all but the lowest dose tested in the old dogs fed the clonidine-containing diet. Old dogs had plasma gh concentration that exceeded that of young dogs when higher doses of clonidine were used.
A clonidine (100 μg/kg)-supplemented diet was fed to middle-aged dogs twice daily for 30 days. Significant (P < 0.01) increase of plasma gh concentration was observed on the first day of the feeding trial, but was undetectable by day 30. After feeding the clonidine-enhanced diet for 30 days, the effects on thymic morphology were variable, and there was no effect on plasma thymulin titer. Clonidine-fed dogs had significantly increased lymphocyte blastogenic responsiveness to mitogens, compared with that of control dogs, when evaluated as stimulation index.
Abstract
Objective
To evaluate the safety and efficacy of avirulent live Salmonella choleraesuis strain 54 (SC54) as a vaccine to protect calves against salmonellosis caused by S dublin.
Animals
40 head of clinically normal 3 to 5-week-old male Holstein calves that were culture negative for Salmonella sp.
Procedure
Calves were randomly assigned to 4 test groups of 10 calves each. Group 1 received 8.5 × 107 colony-forming units (CFU) of SC54 SC. Groups 2 and 3 received 1.13 × 109 CFU of SC54, SC and intranasally, respectively. Group 4 received saline solution as a vaccine control. All calves were challenge exposed orally with 1.74 × 109 CFU of virulent S dublin 14 days after vaccination. Clinical signs and Salmonella shedding were monitored for 28 days after vaccination. Calves were necropsied, and organs were cultured for Salmonella sp 14 days after challenge exposure.
Results
Calves of groups 2 and 3 had slightly high rectal temperature after vaccination. Salmonella dublin challenge exposure resulted in mild clinical signs of salmonellosis. All vaccinated groups had significantly (P< 0.05) lower rectal temperature, fecal shedding of S dublin, and recovery of S dublin from organs after necropsy. SC54 was not recovered from fecal or blood samples collected after vaccination or from injection site samples or organs collected at necropsy.
Conclusions
SC54 given intranasally or SC to calves was safe and significantly (P < 0.05) reduced clinical signs and bacterial shedding after oral challenge exposure with S dublin.
Clinical Relevance
SC54 has potential as an effective vaccine to aid in prevention of salmonellosis caused by S dublin in calves. (Am J Vet Res 1997;58: 265–271)
