Detection of the circular features of the three plasmids by PFGE. (A-C) Plasmid detection by PFGE separation and Southern blot hybridization. A, hybridization with lcp3-specific probes after PFGE separation; B, hybridization with lcp2-specific probes after PFGE separation; C, hybridization with lcp1-specific probes after PFGE separation. The left side of each picture represents PFGE separation of genomic DNA while the right side represents Southern blot hybridization with plasmid-specific probes; M, bacteriophage λ DNA multimer marker (monomer =48.5 kb). ND, undigested DNA; AscI, NotI, BssHII, SmaI, and XhoI represent L. interrogans strain 56609 digested with these enzymes. L. interrogans serovar Lai strain 56601 genomic DNA was also blotted onto a nylon membrane as a negative control. The primers for the synthetized probes are listed in Additional file 1: Table S3.