Salmonella Typhimurium LPS mutations for use in vaccines allowing differentiation of infected and vaccinated pigs

摘要

Contaminated pork is a major source of human salmonellosis and the serovar most frequently isolated from pigs is Salmonella Typhimurium. Vaccination could contribute greatly to controlling Salmonella infections in pigs. However, pigs vaccinated with the current vaccines cannot be discriminated from infected pigs with the LPS-based serological tests used in European Salmonella serosurveillance programmes. We therefore examined which LPS encoding genes of Salmonella Typhimurium can be deleted to allow differentiation of infected and vaccinated pigs (DIVA), without affecting the vaccine strain's protective capacity. For this purpose, deletion mutants in Salmonella strain 112910a, used as vaccine strain, were constructed in the LPS encoding genes: Delta rfbA, Delta rfaL, Delta rfaI, Delta rfaG and Delta rfaF. Primary inoculation of BALB/c mice with the parent strain, Delta rfaL, Delta rfbA or Delta rfaJ strain but not the Delta rfaG, Delta rfaF or Delta rfaI strain protected significantly against subsequent infection with the virulent Salmonella Typhimurium strain NCTC12023. Immunization of piglets with the Delta rfaJ or Delta rfaL mutants resulted in the induction of a serological response lacking detectable antibodies against LPS. This allowed a clear differentiation between sera from pigs immunized with the Delta rfaJ or Delta rfaL strains and sera from pigs infected with their isogenic wild type strain. In conclusion, applying deletions in the rfaJ or the rfaL gene in Salmonella Typhimurium strain 112910a allows differentiation of infected and vaccinated pigs in an LPS based ELISA without reducing the strain's protective capacities in mice