Role of Typhoid Antigens in Protection and Pathogenicity for Mice

Abstract

Swiss white mice immunized with acetone-killed vaccines prepared from strains of Salmonella typho.sa, S. typhimurium, and mouse-virulent S. typhimurium hybrids which had acquired, by conjugal genetic transfer, the S. typhosa antigens 9, Vi, and d were challenged with the S. typhimurium hybrids and with the S. tvphimurium parent strain. The results of' these experiments suggested that the Salmonella somatic antigens were important in conf'erring protection against death in this system. The S. typhosa Vi antigen did not appear to play any signif'icant role in this protection. The S. typhimurium hybrids employed in these studies did not show any loss of mouse virulence as the consequence of' acquisition of various combinations of the S. typhosa somatic, flagella, or Vi antigens, nor did S. typhosa hybrids which had acquired the somatic antigen of S. typhimurium show any increase in mouse virulence.A previous report (1) described the formation of Salmonella typhimurium hybrids expressing antigens 9, Vi. and d by genetic crosses between a S. typhimurium recipient and a S. t,vphosa Hf'r donor. These hybrids retained the same degree of' mouse virulence as their S. typhimurium parent when tested with either C57 black or Swiss white mice. Furthermore, vaccination of' mice with S. typhosa vaccines conferred significant protection against challenge by these hybrid strains but not against their S. typhimurium parent. However, no conclusions were made regarding the protective role of individual S. tvphosa antigens. In the present report, further studies with this system are described which suggest that the somatic antigens are of' primary importance in conferring protection.MATERIALS AND METHODS Mating procedures. S. typhimurium hybrids were obtained by the method previously described (1). Briefly, overnight broth cultures (Penassay broth, Difco) of donor and recipient strains were centrifuged and resuspended in fresh broth. The concentrations of cells were adjusted to approximately 108/ml for the recipient and 2 x 108/ml for the donor. The donor suspension (0.1 ml) was then spread over 0.

Mouse protective capabilities of Escherichia coli hybrids expressing Salmonella typhi antigens

“…Furthermore, addition of the S. typhi Vi antigen to E. coli hybrid F1061 (creating E. coli hybrid WR3078) did not produce a hybrid with better protective capability than F1061, which expresses only the S. typhi somatic antigens 9 and 12. The failure of Vi antigen addition to enhance the protective capability of F1061 is not only similar to our earlier observations with acetone-killed S. typhimurium hybrids as vaccinating strains (1), but is also consistent with our previous findings with regard to the Vi antigen in that we have yet to discover any role for it in the protection conferred in this system (1)(2)(3)(4). Although our comparisons of the protective capabilities of E. coli hybrid F1061 and its parent F464 consistently indicated the importance of the S. typhi somatic antigens expressed by the hybrid, it would appear, nevertheless, that a substantial percentage of the overall ability of F1061 to confer protection in this system derives from the parent strain, F464, itself.…”

“…The E. coli hybrid WR3078, expressing the Vi antigen in addition to its S. typhi 9 and 12 somatic antigens, showed no improvement over E. coli hybrid F1061, with only 55% of the immunized mice surviving the challenge. The failure of Vi antigen addition to enhance the protection afforded by a hybrid expressing the S. typhi somatic antigens has been observed previously in studies using S. typhimurium hybrids (acetone killed) as vaccinating strains (1).…”

“…E. coli hybrid WR3078 was generated by a mating between S. typhi Hfr WR4000 and a melibiose nonutilizing (mel) mutant of E. coli hybrid F1061; it was selected for receipt of the S. typhi mel genes, to which the structural genetic determinants of the Vi antigen (viaB) are closely linked (10), and it expresses the S. typhi Vi antigen in addition to the S. typhi somatic antigens 9 and 12. The derivation of S. typhimurium hybrid H42 has been described previously (1,2); it expresses the 9, 12, Vi, and d antigens of S. typhi and has a 50% lethal dose of less than 50 organisms. The classical Ty2 strain of S. typhi is, of course, well known.…”

“…We previously reported using mouse-virulent Salmonella typhimurium hybrids expressing Salmonella typhi antigens as challenge organisms in vaccinated Swiss-Webster white mice to test the protective abilities of typhoid vaccines (1)(2)(3)(4)). This assay system has proven capable of demonstrating differences in effectiveness among various kinds of typhoid vaccines with respect to their ability to confer protection against death of the animals (2)(3)(4) and has provided evidence that the Salmonella somatic antigens are important in conferring this protection (1). Although our earlier studies employed only nonliving vaccines administered intraperitoneally (i.p.…”

Construction and characterization of isogenic O‐antigen variants of Salmonella typhi

“…1991). Strains C5 his (01,4,5.12;H-i) and WR5005 (01,9,12;H-i) were the generous gift of Dr L. Baron, Waiter Reed Army Institute, Washington, D.C. and are described by Diena et al (1974). The 0-antigen agglutinating pattem of all Salmonella strains was tested using polyclonal 0-antigen-specific rabbit antisera from Difco and Acuro Chemical.…”