Mutations at rfc or pmi attenuate Salmonella typhimurium virulence for mice

Abstract

Insertion mutations were constructed in cloned pmi and rfc genes of Salmonella typhimurium, and these mutations were recombined (singly) into the chromosome of mouse-virulent S. typhimurium Cr, displacing the wild-type alleles. Phage sensitivity profiles, lipopolysaccharide analysis, and DNA blotting all confirmed that the replacement events had occurred. The mutations were complementd by plasmid-borne wild-type alleles, as judged by the restoration of wild-type phage plaquing profiles and lipopolysaccharde production (both mutants) and the restoration of pmi-encoded enzyme production (pmi mutant). The cirulence, persistence, and immunizing capacities of the mutants fed to mice were compared with those of the wild-type strain and complemented mutants. Both mutants were much reduced in virulence, with the rfc mutant being avirulent even at 109 bacteria per mouse. This mutant was also avirulent at up to 106 bacteria per mouse when administered intraperitoneally. Both the rfc and pmi mutant strains persisted in the Peyer's patches of the gut after feeding and were capable of colonizing the Departmenter tissues of the mice from such initial infective foci. Both mutant strains were effective as live oral vaccines (107 bacteria or more) against oral S. typhimurium challenge (104 50% lethal doses; 6 x 108 bacteria) in mice.