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Phylogenetic tree of ctxB genotypes of this study. The tree was constructed by unweighted pair-group method with arithmetic mean based on ctxB amino-acid sequences. One thousand bootstrap replicates were performed for each analysis. The reference amino-acid sequences of different ctxB were from GenBank. G1–G9, genotypes 1–9. The black triangle represents 113 isolates belonging to ctxB genotype 3.
