FIG. 1.

Identification of the virulence plasmids in Salmonella typhimurium. (Upper panel) Visualization of Salmonella plasmids by agarose gel electrophoresis after extraction by the method of Kieser (15). Lanes 1 and 22, E. coli V517 plasmids used as molecular size standards (kbp are indicated on the left of the gel); lane 2, plasmid pIP1350 containing the spvCD-orfE virulence determinant was used as a positive control; lanes 3 to 21, selected virulent Salmonella isolates S1, S3, S7, S15, S16, S22, S39, S40, S41, S42, S43, S49, S50, S51, S53, S54, S55, S57, and S58, respectively. Chromosomal DNA bands (arrow) are seen in each lane. (Lower panel) Autoradiogram of the plasmids after Southern transfer and hybridization with the spvCD-orfE probe.