Conservation of Salmonella typhimurium virulence plasmid maintenance regions among Salmonella serovars as a basis for plasmid curing.

The association of large plasmids with virulence in invasive Salmonella serovars has led to a number of studies designed to uncover the role of these plasmids in virulence. This study addresses two aspects of virulence-associated plasmids. The first is the distribution of the replication and maintenance regions among the plasmids of different Salmonella serovars, and the second is the use of the conserved virulence plasmid par region to provide a rapid method for eliminating the virulence plasmids specifically. Colony blots revealed that the par and repB regions of the S. typhimurium virulence plasmid hybridized with 80% of the isolates of S. choleraesuis, S. dublin, S. enteritidis, S. gallinarum, S. pullorum, and S. typhimurium, while the repC region was not detected in any of the isolates of S. dublin, S. gallinarum, or S. pullorum. None of these maintenance regions was found in any of the 30 additional serovars tested. The large plasmids of those serovars that hybridized with par were labeled with a Kmr insert within parA via P22HTint or P1L4 transduction, which destabilized the plasmids and allowed the rapid isolation of plasmid-free derivatives for all of the serovars, except for S. dublin, which exhibited weak homology with par.