Characterization of the plasmid genes blaT-4 and blaT-5 which encode the broad-spectrum beta-lactamases TEM-4 and...

We have determined the nucleotide sequence of the plasmid genes blaT-4 and blaT-5 which encode the broad-substrate-range beta-lactamases TEM-4 and TEM-5, respectively. The TEM-4 enzyme, which confers high-level resistance to cefotaxime (Ctx) and ceftazidime (Caz), differed from the TEM-1 penicillinase by four amino acid substitutions. Two of the mutations are identical to those responsible for the wide substrate range of the TEM-3 beta-lactamase which hydrolyses Ctx and Caz. The amino acid sequence of TEM-5, which confers higher levels of resistance to Caz than to other recently developed cephalosporins, differed from that of TEM-1 by three mutations distinct from those of TEM-4. Analysis of the location of the mutations in the primary and tertiary structures of class A beta-lactamases suggests that interactions between the substituted residues and beta-lactam antibiotics non-hydrolysable by TEM-1 and TEM-2 allow TEM-4 and TEM-5 to hydrolyse efficiently novel broad-spectrum cephalosporins such as Ctx and Caz.