A novel extended-spectrum TEM-type β-lactamase (TEM-52) associated with decreased susceptibility to moxalactam in Klebsiella pneumoniae

Klebsiella pneumoniae NEM865 was isolated from the culture of a stool sample from a patient previously treated with ceftazidime (CAZ), Analysis of this strain by the disk diffusion test revealed synergies between amoxicillin-clavulanate (AMX-CA) and CAZ, AMX-CA and cefotaxime (CTX), AMX-CA and aztreonam (ATM), and more surprisingly, AMX-CA and moxalactam (MOX). Clavulanic acid (CA) decreased the MICs of CAZ, CTX, and MOX, which suggested that NEM865 produced a novel extended-spectrum beta-lactamase, Genetic, restriction endonuclease, and Southern blot analyses revealed that the resistance phenotype was due to the presence in NEM865 of a 13.5-kb mobilizable plasmid, designated pNEC865, harboring a Tn3-like element, Sequence analysis revealed that the blaT gene of pNEC865 differed from bla(TEM-1) by three mutations leading to the following amino acid substitutions: Glu(104)-->Lys, Met(182)-->Thr, and Gly(238)-->Ser (Ambler numbering). The association of these three mutations has thus far never been described, and the blaT gene carried by pNEC865 was therefore designated bla(TEM-52). The enzymatic parameters of TEM-52 and TEM-3 were found to be very similar except for those for MOX, for which the affinity of TEM-52 (K-i, 0.16 mu M) was 10-fold higher than that of TEM-3 (K-i, 1.9 mu M). Allelic replacement analysis revealed that the combination of Lys(104), Thr(182), and Ser(238) was responsible for the increase in the MICs of MOX for the TEM-52 producers.