Assay of Typhoid Vaccines with Salmonella typhosa-Salmonella typhimurium Hybrids

Abstract

Salmonella typhimurium hybrids expressing the S. typhosa antigens 9, d, and Vi were constructed by genetic crosses with an S. typhosa Hfr donor. The hybrids retained the same degree of mouse virulence as their S. typhimurium parent strain, the minimum lethal dose being less than 50 organisms when tested either in C57 black mice or Swiss white mice. Vaccination of the Swiss white mice with S. typhosa Ty2 vaccines prepared by acetone treatment, alcohol treatment, or heat-killing conferred significant protection against challenge by the hybrid strains but not against their S. typhimurium parent. Both the acetone-treated and alcohol-treated typhoid vaccines were markedly more protective than the heat-killed, phenol-preserved vaccine.

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.…”

“…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.…”

Role of Typhoid Antigens in Protection and Pathogenicity for Mice

“…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.…”

“…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.…”