Figure 3: Distribution of the total β-lactamase occurrences by molecular class and by motility for bacterial species (Appendix-A). Class stands for the Ambler classification of β-lactamases, which divides these enzymes into four molecular classes, A, B, C, and D, based on their conserved and unique amino acid motifs. Class A, C, and D are serine β-lactamases and Class B is metallo- β-lactamases.