Biochemical-Genetic Analysis and Distribution of FAR-1, a Class A β-Lactamase from Nocardia farcinica

From genomic DNA of the clinical isolate Nocardia farcinica VIC, a 1.6-kb Sau3AI fragment was cloned and expressed in Escherichia coli JM109. The recombinant strain expressed a β-lactamase (pI, 4.6), FAR-1, which conferred high levels of resistance to amoxicillin, piperacillin, ticarcillin, and cephalothin. The hydrolysis constants (k(cat), K(m), K(i), and 50% inhibitory concentration) confirmed the MIC results and showed that FAR-1 activity is inhibited by clavulanic acid and at a low level by tazobactam and sulbactam. Moreover, FAR-1 β-lactamase hydrolyzes aztreonam (at a low level) without significant activity against ceftazidime, cefotaxime and imipenem. FAR-1 mature protein of molecular mass ca 32 kDa, has less than 60% amino acid identity with any other class A β-lactamases, being most closely related to PEN-A from Burkholderia cepacia (52%). A bla(FAR-1)-like gene was found in all studied N. farcinica strains, underlining the constitutive origin of this gene.