Dendrogram depicting the genetic relationships between the IncA/C plasmids based on Pst I fingerprints. The dendrogram was constructed with the UPGMA algorithm using Dice coefficients with a 1.0% band position tolerance. The two main groups (designated as types I and II) are separated by a dotted line (similarity index <50%). The five clusters formed at similarity index values >80% are indicated by the letters a to e. Cluster b containing the blaCMY-2-negative strains within type I is highlighted with a dotted box. The donor column refers to Typhimurium strains used as DNA sources for the transformation of E. coli TOP10 or DH5α. The XbaI column indicates the cluster name in which the donor strain was placed in the previously published PFGE-XbaI restriction dendrogram . The CMY column denotes blaCMY-2-positive (+) and blaCMY-2-negative (-) plasmids. The phenotype column describes the resistance phenotype of the donor strain and the resistances transferred by the IncA/C plasmids (underlined). The abbreviations for the antibiotics are described in Methods. The estimated plasmid sizes are indicated in terms of bp. The next ten columns display the results of the PCR screening scheme (Additional file 1, Table S1, Figure 3, Figure 4 and Methods). Positive amplifications are designated by a plus symbol (+) and negative amplifications by a minus symbol (-). In the case of the IP-1 and floR columns, the + (-) code indicates that the Typhimurium donor strain was positive for the marker but that the E. coli transformants were negative. "1 kb" indicates an integron of around 1,000 bp amplified in pAR060302, as previously described by Call et al. . nd, not determined.