A novel extended-spectrum TEM-type beta-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 blaTEM-1 by three mutations leading to the following amino acid substitutions: Glu104-->Lys, Met182-->Thr, and Gly238-->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 blaTEM-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 (Ki, 0.16 microM) was 10-fold higher than that of TEM-3 (Ki, 1.9 microM). Allelic replacement analysis revealed that the combination of Lys104, Thr182, and Ser238 was responsible for the increase in the MICs of MOX for the TEM-52 producers.
Poyart
C
C
Laboratoire de Microbiologie, Faculté de Médecine Necker-Enfants Malades, Paris, France. cpoyart@pasteur.fr
Mugnier
P
P
Quesne
G
G
Berche
P
P
Trieu-Cuot
P
P
D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D003001:Cloning, Molecular; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009070:Moxalactam / Q000378:metabolism / Q000494:pharmacology*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics*
D000900:Anti-Bacterial Agents; D001618:beta-Lactamases; D009070:Moxalactam