Schematic representation indicating the relative positions of the molecular markers used to characterize IncA/C plasmids. Seven regions distributed throughout the reported IncA/C plasmids [5–8, 10] were detected by PCR in the 45 ST213 Typhimurium isolates. Antimicrobial resistance determinants are indicated in red. The 2,589-bp repA/C region includes the complete repA gene, which is involved in plasmid replication and incompatibility group determination. floR is a 1,050-bp region spanning almost the complete floR gene coding for chloramphenicol resistance. The insertion of the CMY island into the plasmid backbone between traC and traA was evaluated by PCR D and PCR G for the right junction, and by PCR A and B for the left junction (see Additional file 1, Table S1, Figure 4 and Results). Two regions included in the IncA/C plasmid PCR typing scheme proposed by Welch et al.  were analyzed. The 1,431-bp Region 7 (R-7) includes the bet gene coding for a phage recombination protein. Region 8 (R-8) is a DNA fragment of 1,600 bp that contains the dcm gene coding for a DNA methylase. The presence of the mercury resistance operon (mer), frequently associated with the Tn21 transposon [7, 8], was evaluated by the amplification of a 2,185-bp region spanning from merA to merT. The presence of IP-1 (dfrA12, orfF and aadA2) was assessed using primers targeting its conserved sequences.