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The virulence plasmid of Salmonella typhimurium is self-transmissible

B M Ahmer1, M Tran, F Heffron

  • 1Department of Molecular Microbiology and Immunology, Oregon Health Sciences University, Portland, Oregon 97201-3098, USA. ahmerb@ohsu.edu

Journal of Bacteriology
|February 11, 1999
PubMed

Insights

The Salmonella Typhimurium virulence plasmid is self-transmissible, contrary to previous reports. Optimal conditions for this plasmid transfer were identified, involving specific mating methods and recipient strains.

Area of Science:

  • Microbiology
  • Bacterial Genetics

Background:

  • Most Salmonella enterica serovar Typhimurium isolates possess a 90-kb virulence plasmid.
  • This plasmid was previously characterized as mobilizable but nonconjugative.

Purpose of the Study:

  • To investigate the conjugative ability of the Salmonella Typhimurium virulence plasmid.
  • To identify optimal conditions for the plasmid's self-transmission.

Main Methods:

  • Conjugation experiments were performed using different Salmonella Typhimurium strains (LT2, 14028, SR-11, SL1344).
  • Filter matings on M9 minimal glucose plates and liquid matings were compared.
  • Recipient strains with and without the virulence plasmid were utilized.
  • Homology analysis of plasmid genes with known conjugation factors was conducted.

Main Results:

  • The virulence plasmids of Salmonella Typhimurium strains LT2, 14028, and SR-11 were found to be self-transmissible.
  • The virulence plasmid of strain SL1344 was determined to be non-self-transmissible.
  • Optimal conjugation frequency (2.9 x 10(-4) transconjugants/donor) was achieved using filter matings on M9 minimal glucose plates with a plasmid-free recipient.
  • Less efficient transfer occurred on Luria-Bertani plates, in liquid matings, or with recipient strains already harboring the virulence plasmid, with efficiency reduced up to 400-fold.
  • Physical location and requirement of F plasmid conjugation gene homologs on the virulence plasmid for self-transmission were confirmed.

Conclusions:

  • The Salmonella Typhimurium virulence plasmid is capable of self-conjugation, challenging prior assumptions.
  • Specific environmental and genetic conditions significantly influence the efficiency of virulence plasmid transfer.
  • The presence of F plasmid conjugation gene homologs is crucial for the observed conjugative phenotype of the virulence plasmid.

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