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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Agroecosystems Management Research » Research » Publications at this Location » Publication #306093
Title: An rfaH mutant of Salmonella enterica serovar typhimurium is attenuated in swine and reduces intestinal colonization, fecal shedding, and disease severity due to virulent Salmonella Typhimurium

Author
item Bearson, Bradley - Brad
item Bearson, Shawn
item KICH, JALUSA - Embrapa-Pigs And Poultry
item LEE, IN - Hannam University

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2014
Publication Date: 10/9/2014
Publication URL: https://handle.nal.usda.gov/10113/60365
Citation: Bearson, B.L., Bearson, S.M., Kich, J.D., Lee, I.S. 2014. An rfaH mutant of Salmonella enterica serovar typhimurium is attenuated in swine and reduces intestinal colonization, fecal shedding, and disease severity due to virulent Salmonella Typhimurium. Frontiers in Veterinary Science. Available: http://dx.doi.org/10.3389/fvets.2014.00009.

Interpretive Summary: Pigs often have the human foodborne pathogen Salmonella in their gastrointestinal tract, but they typically do not show signs of illness. Salmonella in these 'carrier' pigs can contaminate our food supply, either through pork products that go to market or if the manure from pigs that are shedding Salmonella is used as a fertilizer on food crops that are not cooked prior to consumption. Therefore, interventions are needed to limit Salmonella in pigs to enhance food safety and reduce environmental contamination. Our research group created a live Salmonella vaccine that, when given to pigs, reduces the ability of other Salmonella (that cause human foodborne disease) to inhabit the pigs. Furthermore, the specific design of the vaccine prevents its detection by commercial kits that test for the Salmonella status of swine herds, thereby providing the ability to differentiate infected versus vaccinated animals (DIVA). Because most foodborne disease agents are transferred to humans from animals/animal products, interventions in the animal reservoir are necessary to fully optimize control strategies. We anticipate that this Salmonella vaccine will support food safety and public health by reducing the spread of human foodborne Salmonella in pigs and may also benefit other livestock industries.

Technical Abstract: Swine are often asymptomatic carriers of Salmonella spp., and interventions are needed to limit colonization of swine to enhance food safety and reduce environmental contamination. We evaluated the attenuation and potential vaccine use in pigs of a Salmonella enterica serovar Typhimurium mutant of rfaH, the gene encoding the RfaH antiterminator that prevents premature termination of long mRNA transcripts. Pigs inoculated with wild-type S. Typhimurium exhibited a significant elevation in average body temperature (fever) at 1 and 2 days post-inoculation (n=5/group); rfaH-inoculated pigs did not. During the 7-day trial, a significant reduction of Salmonella in the feces, tonsils, and cecum were observed in the rfaH-inoculated pigs compared to wild-type inoculated pigs. To determine whether vaccination with the rfaH mutant could provide protection against wild-type S. Typhimurium challenge, two groups of pigs (n=14/group) were inoculated with either the rfaH mutant or a PBS placebo at 6 and 8 weeks of age and challenged with the parental, wild-type S. Typhimurium at 11 weeks of age. The average body temperature was significantly elevated in the mock-vaccinated pigs at 1 and 2 days post-challenge, but not in the rfaH-vaccinated pigs. Fecal shedding at 2 and 3 days post-challenge and colonization of gastrointestinal tract tissues at 7 days post-challenge by wild-type S. Typhimurium was significantly reduced in the rfaH-vaccinated pigs compared to mock-vaccinated pigs. Serological analysis using the IDEXX HerdChek Swine Salmonella Test Kit indicated that vaccination with the rfaH mutant did not stimulate an immune response against LPS. These results indicate that vaccination of swine with the attenuated rfaH mutant confers protection against challenge with virulent S. Typhimurium but does not interfere with herd level monitoring for Salmonella spp., thereby allowing for differentiation of infected from vaccinated animals (DIVA).