Page "Beta-lactamase" Paragraph 9

Group 2 are penicillinases, cephalosporinases, or both inhibited by clavulanic acid, corresponding to the molecular classes A and D reflecting the original TEM and SHV genes.

However, because of the increasing number of TEM-and SHV-derived β-lactamases, they were divided into two subclasses, 2a and 2b.