Characterization of attenuated Salmonella C500 strain with a Dasd mutant and use as an Asd+ balanced-lethal host-vector system

Abstract:

Salmonella enterica serovar Choleraesuis strain C500 is a live, attenuated vaccine that has been used in China for over 40 years to prevent piglet paratyphoid. The objective of this study was to evaluate the potential of attenuated Salmonella enterica serovar Choleraesuis C500 strain with a Dasd mutant as an effective live vaccine vector by the Asd+ balanced-lethal host-vector system. Here, we compared the characteristics of S. enterica serovar Choleraesuis DasdC500 strain with the parent C500 strain, including phenotype, growth rate, virulence, safety, and expression for heterologous antigen. The mean generation times of ΔasdC500 mutant, the vector control DasdC500(pYA3493), and the parent avirulent C500 vaccine strain in Luria broth were 30.7, 28.1, and 27.9 min, respectively. The fermentation patterns of theses three strains on different carbohydrates, and the levels of production of H2S, were similar. The O and H antigens of DasdC500 mutant, DasdC500(pYA3493) and DasdC500(pYA-F1P2) were 6,7:C:1,5, identical to the parent strain C500. By the method of Reed and Muench, groups of mice were challenged by the intraperitoneal route with different amounts of DasdC500(pYA3493) or the parent C500 strain, and the virulence of DasdC500(pYA3493) with LD50 of 1.1×107 CFU was a little lower than C500 with LD50 of 4.4×106 CFU. All piglets inoculated with DasdC500(pYA3493) or C500 survived, and no signs of disease were observed during the entire experimental period. No major differences were found in these two groups. In addition, the recombinant pYA-F1P2 plasmid was very stable in the recombinant DasdC500(pYA-F1P2) strain, which expressed secretorily a large amount of the recombinant filamentous hemagglutinin type I domain and pertactin region 2 domain antigen (rF1P2) of Bordetella bronchiseptica. In this study, we have shown that the DasdC500 mutant had a series of biological characteristics silimar to the parent vaccine strain C500. Furthermore, the strain could express secretorily a large amount of heterologous antigen. It is likely that this Salmonella expression and delivery system could be easily adapted to develop multivalent recombinant Salmonella vaccines against infectious agents using the Asd+ balanced-lethal host-vector system.