Identification and mapping of mba regions of the Salmonella choleraesuis virulence plasmid pKDSC50 responsible for mouse bacteremia.

A restriction cleavage map was constructed for pKDSC50, the 50 kb virulence plasmid of Salmonella choleraesuis. Using Tn1 transposon-insertion mutagenesis, we obtained 19 mutant strains of S. choleraesuis with a diminished ability to cause bacteremia in the mouse. pKDSC50::Tn1 DNA of the mutant strains was extracted and introduced into a pKDSC50-cured S. choleraesuis strain. Nine of the 19 transformants showed the diminished ability to cause mouse bacteremia. Tn1-insertion of the nine mutant strains was clustered within a 6.2 kb segment of pKDSC50, demonstrating that this region was necessary for conferring ability to cause mouse bacteremia (Mba) on the host organism. Two regions, mba-1 and mba-2, were identified within the 6.2 kb fragment. In E. coli minicells, the cloned fragments containing the mba region expressed at least three proteins with apparent molecular weights of 29,000, 32,000 and 32,000.