Hydrolyzes beta-lactam antibiotics such as penicillin G, carbenicillin, cephaloridine, cefoxitin, cefotaxime, ceftazidime, and aztreonam. Has especially increased relative hydrolysis rates for cephalothin, cephaloridine, cefotaxime and ceftizoxime. a beta-lactam + H2O = a substituted beta-amino acid Inhibited 16-fold better by the beta-lactamase inhibitor tazobactam than by clavulanic acid. Belongs to the class-A beta-lactamase family.