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Mutations at rfc or pmi attenuate Salmonella typhimurium virulence for mice
L V Collins1, S Attridge, J Hackett
1Department of Microbiology, University of Adelaide, Australia.
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 C5, displacing the wild-type alleles. Phage sensitivity profiles, lipopolysaccharide analysis, and DNA blotting all confirmed that the replacement events had occurred. The mutations were complemented by plasmid-borne wild-type alleles, as judged by the restoration of wild-type phage plaquing profiles and lipopolysaccharide production (both mutants) and the restoration of pmi-encoded enzyme production (pmi mutant). The virulence, 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 10(9) bacteria per mouse. This mutant was also avirulent at up to 10(6) 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 deeper tissues of the mice from such initial infective foci. Both mutant strains were effective as live oral vaccines (10(7) bacteria or more) against oral S. typhimurium challenge (10(4) 50% lethal doses; 6 x 10(8) bacteria) in mice.
Insights
Salmonella typhimurium mutants lacking pmi or rfc genes show reduced virulence but retain oral vaccine potential. These attenuated Salmonella strains offer promise for developing effective live oral vaccines against typhoid fever.
Area of Science:
- Microbiology
- Immunology
- Bacteriology
Background:
- Salmonella typhimurium is a significant pathogen causing enteric infections.
- Understanding the genetic basis of Salmonella virulence is crucial for developing effective vaccines.
- The pmi and rfc genes play roles in Salmonella pathogenesis and cell surface structure.
Purpose of the Study:
- To investigate the role of pmi and rfc genes in Salmonella typhimurium virulence and immunogenicity.
- To assess the potential of pmi and rfc mutants as live oral vaccines.
Main Methods:
- Construction of insertion mutations in cloned pmi and rfc genes.
- Recombination of mutations into the S. typhimurium C5 chromosome.
- Confirmation of genetic modifications using phage sensitivity, LPS analysis, and DNA blotting.
- Complementation of mutants with wild-type alleles.
- Evaluation of virulence, persistence, and immunizing capacity in a mouse model.
Main Results:
- Both pmi and rfc mutants exhibited significantly reduced virulence in mice.
- The rfc mutant was avirulent even at high doses (10^9 bacteria orally, 10^6 intraperitoneally).
- Mutant strains persisted in Peyer's patches and colonized deeper tissues.
- Both mutant strains demonstrated effectiveness as live oral vaccines against S. typhimurium challenge.
Conclusions:
- The pmi and rfc genes are important for Salmonella typhimurium virulence.
- Attenuated Salmonella mutants lacking pmi or rfc are promising candidates for live oral vaccines.
- These mutants can elicit protective immunity against homologous challenge.