Molecular characterization of TEM-59 (IRT-17), a novel inhibitor-resistantTEM-derived beta-lactamase in a clinical isolate of Klebsiella oxytoca

A clinical isolate of Klebsiella oxytoca (Kox 443) was found to have a low- level resistance to broad-spectrum penicillins (MICs of amoxicillin and tic arcillin, 256 and 32 mu g/ml, respectively), without substantial potentiati on by 2 mu g of clavulanic acid per mi (amoxicillin- and ticarcillin-clavul anate, 128 and 8 mu g/ml, respectively), while being fully susceptible to c ephalosporins and other beta-lactam antibiotics. These resistances were car ried by a ca, 50-kb conjugative plasmid that encodes a single beta-lactamas e alh a pI of 5.6. Compared to TEM-2, this enzyme exhibited a 3- to 30-fold higher K-m and a decreased maximal hydrolysis rate for beta-lactams; highe r concentrations of suicide inactivators (5- to 500-fold higher concentrati ons giving a 50% reduction in hydrolysis) were required for inhibition. Nuc leotide sequence analysis revealed identity between the bla(TEM) gene of Ko x 443 and the bla(TEM-2) gene, except for a single A-to-G change at positio n 590, leading to the amino acid change from Ser-130 Gly, This mutation has not been reported previously in the TEM type beta-lactamases produced by c linical strains, and the novel enzyme was called TEM-59 (alternative name I RT-17). This is the first description of an inhibitor-resistant TEM-derived enzyme in the species K, oxytoca.