FIG. 2.

Dendrogram of 15 class A β-lactamases. Branch lengths are drawn to scale and proportional to the number of amino acid changes. The bootstrap values are indicated at each node. The β-lactamases used for comparison were PSE-1, PSE-4, and CARB-3 from P. aeruginosa (3, 13, 14), CTX-M-5, CTX-M-3 from S. enterica serovar Typhimurium (4; Gazouli, unpublished), AER-1 from A. hydrophila (25), CARB-6 from V. cholerae (6), ROB-1 from A. pleuropneumoniae (5), B. thuringiensis β-lactamase (36), S. fradiae Y59 β-lactamase (20), OXY-2 from K. oxytoca (8), S. marcescens S5 β-lactamase (20), and β-lactamase from P. mirabilis N-29 (31).