Shakibaie Mohammad Reza, Azizi Omid, Shahcheraghi Fereshteh
Department of Microbiology and Virology, Kerman University of Medical Sciences, Kerman, Iran; Infection Diseases and Tropical Medicine Research Center, Kerman University of Medical Sciences, Kerman, Iran.
Department of Microbiology and Virology, Kerman University of Medical Sciences, Kerman, Iran.
Infect Genet Evol. 2017 Jul;51:118-126. doi: 10.1016/j.meegid.2017.03.018. Epub 2017 Mar 21.
Metallo-β-lactamases (MBLs) such as IMPs are broad-spectrum β-lactamases that inactivate virtually all β-lactam antibiotics including carbapenems. In this study, we investigated the hydrolytic activity, phylogenetic relationship, three dimensional (3D) structure including zinc binding motif of a new IMP variant (IMP-55) identified in a clinical strain of Acinetobacter baumannii (AB). AB strain 56 was isolated from an adult ICU of a teaching hospital in Kerman, Iran. It exhibited MIC 32μg/ml to imipenem and showed MBL activity. Hydrolytic property of the MBL enzyme was measured phenotypically. Presence of bla gene encoded by class 1 integrons was detected by PCR-sequencing. Phylogenetic tree of IMP protein was constructed using the Unweighted Pair Group Method with Arithmetic Mean (UPGMA) and 3D model including zinc binding motif was predicted by bioinformatics softwares. Analysis of IMP sequence led to the identification of a novel IMP-type designated as IMP-55 (GenBank: KU299753.1; UniprotKB: A0A0S2MTX2). Impact in term of hydrolytic activity compared to the closest variants suggested efficient imipenem hydrolysis by this enzyme. Evolutionary distance matrix assessment indicated that IMP-55 protein is not closely related to other A. baumannii IMPs, however, shared 98% homology with Escherichia coli IMP-30 (UniprotKB: A0A0C5PJR0) and Pseudomonas aeruginosa IMP-1 (UniprotKB: Q19KT1). It consisted of five α-helices, ten β-sheets and six loops. A monovalent zinc ion attached to core of enzyme via His95, His97, His157 and Cys176. Multiple amino acid sequence alignments and mutational trajectory with reported IMPs showed 4 amino acid substitutions at positions 12(Phe→Ile), 31(Asp→Glu), 172(Leu→Phe) and 185(Asn→Lys). We suggest that the pleiotropic effect of mutations due to frequent administration of imipenem is responsible for emergence of new IMP variant in our hospitals.
金属β-内酰胺酶（MBLs）如IMP型酶是广谱β-内酰胺酶，几乎能使所有β-内酰胺类抗生素（包括碳青霉烯类）失活。在本研究中，我们调查了在一株鲍曼不动杆菌（AB）临床菌株中鉴定出的一种新型IMP变体（IMP-55）的水解活性、系统发育关系、三维（3D）结构（包括锌结合基序）。AB菌株56分离自伊朗克尔曼一家教学医院的成人重症监护病房。它对亚胺培南的最低抑菌浓度（MIC）为32μg/ml，并表现出MBL活性。通过表型方法测定了MBL酶的水解特性。通过PCR测序检测了1类整合子编码的bla基因的存在。使用算术平均非加权配对组法（UPGMA）构建了IMP蛋白的系统发育树，并通过生物信息学软件预测了包括锌结合基序的3D模型。IMP序列分析导致鉴定出一种新型的IMP类型，命名为IMP-55（GenBank：KU299753.1；UniprotKB：A0A0S2MTX2）。与最接近的变体相比，该酶在水解活性方面的影响表明其能有效水解亚胺培南。进化距离矩阵评估表明，IMP-55蛋白与其他鲍曼不动杆菌IMP型酶关系不密切，然而，它与大肠杆菌IMP-30（UniprotKB：A0A0C5PJR0）和铜绿假单胞菌IMP-1（UniprotKB：Q19KT1）具有98%的同源性。它由5个α螺旋、10个β折叠和6个环组成。一个单价锌离子通过His95、His97、His157和Cys176与酶的核心相连。与已报道的IMP型酶的多氨基酸序列比对和突变轨迹显示，在第12位（苯丙氨酸→异亮氨酸）、31位（天冬氨酸→谷氨酸）、172位（亮氨酸→苯丙氨酸）和185位（天冬酰胺→赖氨酸）有4个氨基酸替换。我们认为，由于频繁使用亚胺培南导致的突变的多效性效应是我们医院出现新IMP变体的原因。
