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首页> 美国卫生研究院文献>Antimicrobial Agents and Chemotherapy >Novel Chimeric β-Lactamase CTX-M-64 a Hybrid of CTX-M-15-Like and CTX-M-14 β-Lactamases Found in a Shigella sonnei Strain Resistant to Various Oxyimino-Cephalosporins Including Ceftazidime
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Novel Chimeric β-Lactamase CTX-M-64 a Hybrid of CTX-M-15-Like and CTX-M-14 β-Lactamases Found in a Shigella sonnei Strain Resistant to Various Oxyimino-Cephalosporins Including Ceftazidime

机译：新型嵌合β-内酰胺酶CTX-M-64是CTX-M-15-Like和CTX-M-14β-内酰胺酶的杂种在耐多种乙酰氨基头孢菌素（包括头孢他啶）的志贺氏志贺菌中发现。

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The plasmid-mediated novel β-lactamase CTX-M-64 was first identified in Shigella sonnei strain UIH-1, which exhibited resistance to cefotaxime (MIC, 1,024 μg/ml) and ceftazidime (MIC, 32 μg/ml). The amino acid sequence of CTX-M-64 showed a chimeric structure of a CTX-M-15-like β-lactamase (N- and C-terminal moieties) and a CTX-M-14-like β-lactamase (central portion, amino acids 63 to 226), suggesting that it originated by homologous recombination between the corresponding genes. The introduction of a recombinant plasmid carrying blaCTX-M-64 conferred resistance to cefotaxime in Escherichia coli, and the activities of cefotaxime and ceftazidime were restored in the presence of clavulanic acid. Of note, CTX-M-64 production could also confer consistent resistance to ceftazidime, which differs from the majority of CTX-M-type enzymes, which poorly hydrolyze ceftazidime. These results were consistent with the kinetic parameters determined with the purified CTX-M-64 enzyme. The blaCTX-M-64 gene was flanked upstream by an ISEcp1 sequence and downstream by an orf477 sequence. The sequence of the 45-bp spacer region between the right inverted repeat (IRR) of ISEcp1 and blaCTX-M-64 was exactly identical to that of ISEcp1-blaCTX-M-15-like. Moreover, the presence of a putative IRR of ISEcp1 at the right end of truncated orf477 is indicative of an ISEcp1-mediated transposition event in the blaCTX-M-64 gene. The emergence of CTX-M-64 by probable homologous recombination would suggest the natural potential of an alternative mechanism for the diversification of CTX-M-type β-lactamases.
机译：质粒介导的新型β-内酰胺酶CTX-M-64首次在索氏志贺氏菌菌株UIH-1中鉴定，该菌株对头孢噻肟（MIC，1,024μg/ ml）和头孢他啶（MIC，32μg/ ml）表现出抗性。 CTX-M-64的氨基酸序列显示CTX-M-15-样β-内酰胺酶（N和C端部分）和CTX-M-14-样β-内酰胺酶（中央部分）的嵌合结构（第63至226位氨基酸），提示其起源于相应基因之间的同源重组。携带blaCTX-M-64的重组质粒的引入赋予了大肠杆菌对头孢噻肟的抗性，并且在棒酸存在下恢复了头孢噻肟和头孢他啶的活性。值得注意的是，CTX-M-64的生产还可以赋予头孢他啶一致的抗性，这与大多数CTX-M型酶不同，后者对头孢他啶的水解较差。这些结果与用纯化的CTX-M-64酶测定的动力学参数一致。 blaCTX-M-64基因的上游是ISEcp1序列，下游是orf477序列。 ISEcp1和blaCTX-M-64的右反向重复序列（IRR）之间的45 bp间隔区序列与ISEcp1-blaCTX-M-15-like序列完全相同。此外，在截短的orf477的右端存在ISEcp1的假定IRR，表明blaCTX-M-64基因中有ISEcp1介导的转座事件。 CTX-M-64可能通过同源重组的出现将提示CTX-M型β-内酰胺酶多样化的另一种机制的自然潜力。

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