Intraperitoneal Mouse Virulence of Salmonella typhimurium Hybrids Expressing Somatic Antigen 9

Salmonella typhimurium hybrids expressing somatic antigen 9after mating witheither S.typhosa orS.enteritidis Hfrdonors didnotdiffer fromtheir S. typhimurium parent withrespect tothenumberoforganisms required to produce deathinmiceinoculated intraperitoneally. Wepreviously reported studies (2,3)inwhich Salmonella typhimurium hybrids expressing S. typhosa antigens astheresult ofgenetic exchange wereemployed inmouseprotection and pathogenicity experiments. Atanintraperitonealdoselevel of50organisms, thedegree of virulence exhibited byS.typhimurium hybrids expressing various combinations ofS.typhosa Vi,flagella d,andsomatic 9antigens wasnot observed todiffer fromthatoftheir virulent S. typhimurium parent. Thisindication thatthe virulence ofthese S.typhimurium hybrids was notaffected bytheir expression ofS.typhosa antigens didnotseemtousatallremarkable; it wastheresult we hadexpected. We were concerned, however, bystudies elsewhere (7,9) inwhichother S.typhimurium hybrids, expressingthesomatic 9 antigen astheresult of inheritance ofS.enteritidis genetic determinants, showeda10-fold decrease intheir virulence formiceuponintraperitoneal injection. Thisdecrease invirulence wasconsidered to haveresulted fromthequalitative change inthe lipopolysaccharide