Institute of Antibiotics, Huashan Hospital, Fudan University, Shanghai, China; Key Laboratory of Clinical Pharmacology of Antibiotics, Ministry of Health, Shanghai, China.
Institute of Antibiotics, Huashan Hospital, Fudan University, Shanghai, China; Key Laboratory of Clinical Pharmacology of Antibiotics, Ministry of Health, Shanghai, China.
Int J Antimicrob Agents. 2024 Sep;64(3):107277. doi: 10.1016/j.ijantimicag.2024.107277. Epub 2024 Jul 19.
Nitrofurantoin is recommended as first-line therapy for the optimal treatment of uncomplicated urinary tract infections (UTIs) caused by enterococci and Escherichia coli. However, the mechanisms of nitrofurantoin resistance in enterococci have not been elucidated. This study aimed to investigate the mechanisms of nitrofurantoin resistance in E. faecium, focusing on the role of the nitroreductase NrmA.
Enterococcus strains isolated from the urinary tract samples were collected and were tested for nitrofurantoin susceptibility. Potential genes associated with nitrofurantoin resistance were screened in the NCBI nucleotide database and by polymerase chain reaction (PCR). Complementation assays and enzyme kinetic tests were performed to assess the impact of the Q48K mutation in NrmA on nitrofurantoin resistance.
Of the 128 E. faecium isolates tested, 59 (46.1%) were resistant to nitrofurantoin. Analysis revealed the presence of a type IB nitroreductase, designated NrmA, in all E. faecium strains studied, shared 18.7% sequence identity with nitroreductase NfsB in E. coli. Different from NrmA in nitrofurantoin-susceptible E. faecium, nitrofurantoin-resistant strains had a single amino acid substitution, i.e., a lysine instead of a glutamine at position 48 (Q48K mutation). Complementation assays of nitrofurantoin-resistant E. faecium HS17-112 showed that the nitrofurantoin minimal inhibitory concentration of the complemented strain HS17-112: pIB166-nrmA (wild type [WT]) decreased from 128 mg/L to 4 mg/L. Compared with NrmA (WT), NrmA (Q48K) showed significantly reduced catalytic efficiency, with a kcat/Km value decreasing from 0.122 µM s to 0.000042 µM s.
The Q48K mutation in nitroreductase NrmA is responsible for nitrofurantoin resistance in E. faecium.
呋喃妥因被推荐为治疗肠球菌和大肠杆菌引起的单纯性尿路感染（UTI）的一线治疗药物。然而，肠球菌对呋喃妥因耐药的机制尚未阐明。本研究旨在探讨屎肠球菌中呋喃妥因耐药的机制，重点研究硝基还原酶 NrmA 的作用。
收集来自尿路感染样本的肠球菌菌株，并进行呋喃妥因药敏试验。在 NCBI 核苷酸数据库和聚合酶链反应（PCR）中筛选与呋喃妥因耐药相关的潜在基因。通过互补实验和酶动力学试验来评估 NrmA 中的 Q48K 突变对呋喃妥因耐药的影响。
在测试的 128 株屎肠球菌中，有 59 株（46.1%）对呋喃妥因耐药。分析表明，所有研究的屎肠球菌菌株均存在一种 I 型硝基还原酶，命名为 NrmA，与大肠杆菌中的硝基还原酶 NfsB 具有 18.7%的序列同一性。与对呋喃妥因敏感的屎肠球菌中的 NrmA 不同，呋喃妥因耐药株的第 48 位氨基酸由谷氨酰胺突变为赖氨酸（Q48K 突变）。对呋喃妥因耐药的屎肠球菌 HS17-112 进行的互补实验表明，互补菌株 HS17-112：pIB166-nrmA（野生型[WT]）的呋喃妥因最小抑菌浓度从 128 mg/L 降至 4 mg/L。与 NrmA（WT）相比，NrmA（Q48K）的催化效率明显降低，kcat/Km 值从 0.122 µM s 降至 0.000042 µM s。
硝基还原酶 NrmA 中的 Q48K 突变导致屎肠球菌对呋喃妥因耐药。
