Comparison of amino-acid sequences of seven representative enzymes in the CTX-M family. Amino-acids are numbered according to the standard numbering scheme for the class A serine β-lactamases, giving the active site serine residue the Ambler number 70. Dots indicate identical amino-acids compared to CTX-M-2. Deletion mutations are expressed with short lines. The underlined amino-acids, 70SXXK73, 107P, 130SDN132, 143GG144, 166E and 234KXG236, represent the conserved residues in typical class A serine β-lactamases.