Confers high levels of resistance to amoxicillin, benzylpenicillin, piperacillin, ticarcillin and cephalothin. Not active against ceftazidime, cefotaxime and aztreonam. a beta-lactam + H2O = a substituted beta-amino acid Inhibited by clavulanic acid. Belongs to the class-A beta-lactamase family.