Department of Biochemistry and Medical Biotechnology, Calcutta School of Tropical Medicine, 108 C.R. Avenue, Kolkata 700073, India.
Department of Biochemistry and Medical Biotechnology, Calcutta School of Tropical Medicine, 108 C.R. Avenue, Kolkata 700073, India.
Int J Antimicrob Agents. 2014 Jun;43(6):518-26. doi: 10.1016/j.ijantimicag.2014.03.002. Epub 2014 Apr 13.
Resistance to third-generation cephalosporins (3GCs) mediated by extended-spectrum β-lactamases (ESBLs) in pathogenic Enterobacteriaceae is considered a major public health threat in India. This study deals with the detection of plasmid-mediated blaCTX-M, blaSHV and blaOXA genes, understanding their contribution to the ESBL phenotype, and their molecular interaction with 3GCs. More than 87% of isolates showed 3GC resistance, with ESBL production in 60.0% of Escherichia coli and 47.7% of Klebsiella pneumoniae. Molecular characterisation revealed the presence of blaCTX-M-15 (29.8%), blaCTX-M-truncated (1.3%), blaCTX-M-27 (0.7%), blaSHV-1 (20.5%), blaSHV-11 (2.0%), blaSHV-42 (0.7%) and blaOXA-1 (9.9%), among which blaCTX-M variants and blaSHV-42 were ESBLs. Phylogenetic analysis predicted strong selection pressure on all blaCTX-M variants, blaSHV-11 and blaSHV-42. The instability index and Gibbs free folding energy change (ΔΔG) predicted decreased stability of SHV-11 and SHV-42. Mutations of CTX-M-truncated, SHV-11 and SHV-42 located in the core region of the enzymes were found to be functional/pathogenic in nature. The catalytic pockets of CTX-M-15 and SHV-42 had the greatest molecular surface area, which might explain their expanded substrate spectrum towards oxyimino-cephalosporins. Molecular dynamics analysis indicated different structural flexibility of CTX-M-truncated compared with the other enzymes. Amino acid alterations resulted in a change of orientation of catalytic residues of class A β-lactamases that might affect their catalytic processes. Molecular interactions revealed higher catalytic efficiency (ΔG and Km) of CTX-M-15, CTX-M-truncated, CTX-M-27, SHV-11 and SHV-42 compared with their respective wild-types. This study provides useful insights into ESBL production of pathogenic Enterobacteriaceae in India that might help in the development of new antibiotics.
在印度，产肠杆菌科细菌对第三代头孢菌素（3GCs）的耐药性由超广谱β-内酰胺酶（ESBLs）介导，被认为是一个主要的公共卫生威胁。本研究涉及检测质粒介导的 blaCTX-M、blaSHV 和 blaOXA 基因，了解它们对 ESBL 表型的贡献，以及它们与 3GCs 的分子相互作用。超过 87%的分离株表现出 3GC 耐药性，其中 60.0%的大肠杆菌和 47.7%的肺炎克雷伯菌产生 ESBL。分子特征表明存在 blaCTX-M-15（29.8%）、blaCTX-M 截断（1.3%）、blaCTX-M-27（0.7%）、blaSHV-1（20.5%）、blaSHV-11（2.0%）、blaSHV-42（0.7%）和 blaOXA-1（9.9%），其中 blaCTX-M 变体和 blaSHV-42 为 ESBL。系统发育分析预测所有 blaCTX-M 变体、blaSHV-11 和 blaSHV-42 都受到强烈的选择压力。不稳定性指数和吉布斯自由折叠能变化（ΔΔG）预测 SHV-11 和 SHV-42 的稳定性降低。在酶的核心区域发现 blaCTX-M 截断、SHV-11 和 SHV-42 的突变具有功能/致病性。CTX-M-15 和 SHV-42 的催化口袋具有最大的分子表面积，这可以解释它们对氧肟头孢菌素的扩展底物谱。分子动力学分析表明，CTX-M-截断与其他酶相比具有不同的结构灵活性。氨基酸的改变导致 A 类β-内酰胺酶催化残基的取向发生变化，这可能影响它们的催化过程。分子相互作用表明，CTX-M-15、CTX-M-截断、CTX-M-27、SHV-11 和 SHV-42 的催化效率（ΔG 和 Km）高于各自的野生型。本研究为了解印度产肠杆菌科细菌的 ESBL 产生情况提供了有用的见解，这可能有助于开发新的抗生素。
