Figure 2.

Phylogenetic relationships of the XXRs. The unrooted dendrograms were compiled from an arbitrary selection of representative repeat sequences from each species harboring a SI. For clarity, branch identifications are omitted for regions of tight clustering and instead are encircled and marked with the type of XXR. XXRs with similarity to the endogenous repeats of another species are indicated by name within the respective encircled regions. The repeat sequences associated with known antibiotic resistance cassettes are boxed and confer resistance to the following compounds: aad, streptomycin–spectinomycin; cat, chloramphenicol; qac, quaternary ammonium compounds; CAR, carbenicillin–ampicillin; dfr, trimethoprim. For XXR nomenclature, see Table 2.