The CcrA beta-lactamase from Bacteroides fragilis TAL3636 was cloned into Escherichia coli and purified from inclusion bodies. This group 3 metalloenzyme hydrolyzed most beta-lactam antibiotics, including cephamycins and carbapenems. Following inhibition by chelators, enzyme activity was recovered with the cations Zn2+ and Co2+. Clavulanate and sulbactam were activators; tazobactam at 10 microM inactivated the enzyme.