FIG. 1.

Neighbor-joining tree of six classes of tet genes encoding efflux pump proteins. The tree was inferred from DNA sequences, and it was arbitrarily rooted with the cmlA5 gene, which encodes an efflux pump protein rendering resistance to chloramphenicol in E. coli. Bootstrap values were calculated from 100 trees, and the number at each node indicates the number of times that the node was supported in the bootstrap analysis. The bar represents a 0.1 estimated change per nucleotide. Each primer pair listed in Table 1 targets a corresponding cluster.