PCR analysis of the plasmids found in tetracycline resistant mutants. PCR with primers G11 and G12 was carried out in order to amplify the selection cartridge of pGBG1 in tetracycline resistant mutants obtained in Brucella. The black arrow indicates the position of the PCR fragment obtained from pGBG1/TcR mutants due to insertions encountered in B. ovis BOC22 and B. pinnipedialis B2/94 strains (Lanes 3, 7, 8, 9, 10, 12, 13, 14 and 15). Mutants due to deletions and point mutations (Lanes 2, 4, 5, 6, 11, 16, 17 and 18) produced PCR products of the same size or smaller than the vector pGBG1 (Lane 1). M: Molecular Weight Marker 1 Kb plus DNA Ladder.1. Lane 19. Negative control (PCR reaction mixture without DNA).