Construction of plasmid-free derivatives of Salmonella typhimurium LT2 using temperature-sensitive mutants of pKZ1 for displacement of the resident plasmid, pSLT.

Replication (or partitioning) temperature-sensitive mutants of pKZ1 were isolated and shown to exhibit incompatibility with the resident plasmid (pSLT) of Salmonella typhimurium LT2. Following displacement of pSLT, the mutant plasmids were effectively eliminated from the cell population by passage at 42 degrees C, yielding plasmid-free isolates.