Asia Pacific Foundation for Infectious Diseases (APFID), Seoul, Republic of Korea.
Division of Infectious Diseases, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.
J Antimicrob Chemother. 2017 Sep 1;72(9):2454-2460. doi: 10.1093/jac/dkx175.
We previously reported the first case of vancomycin treatment failure due to development of vancomycin-intermediate resistance in a patient with an MRSA of ST72, a community genotype in Korea. We investigated two isogenic MRSA strains from this patient, who experienced treatment failure with vancomycin and rifampicin.
We tracked the genetic alterations that confer reduced susceptibility to vancomycin on those two isogenic MRSA strains by WGS.
Five non-synonymous mutations were identified, including rpoB (H481Y), dprA (G196C), femA (F92C), vraR (E127K) and agrC (E391stop). We further studied the role of a mutation of vraR in reduced susceptibility to vancomycin. Introduction of the mutated vraR (E127K) into a vancomycin-susceptible Staphylococcus aureus strain resulted in an increase in vraSR mRNA expression and vancomycin MIC and development of the hetero-VISA phenotype, which was confirmed by the population analysis profile (PAP)/AUC. Electron microscopy showed increased cell wall thickness in the strains with mutated vraR.
Based on the genomic data, molecular experiments and PAP and cell wall analyses, we propose that a single mutation of vraR is associated with the reduced susceptibility to vancomycin in MRSA and further treatment failure.
我们之前报道了首例耐万古霉素中间型金黄色葡萄球菌（ST72，韩国社区型）患者因万古霉素中介耐药性发展而导致万古霉素治疗失败的病例。我们对该患者经历万古霉素和利福平治疗失败的两个同源性耐甲氧西林金黄色葡萄球菌（MRSA）菌株进行了研究。
我们通过 WGS 追踪了导致这两种同源性 MRSA 菌株对万古霉素敏感性降低的遗传改变。
鉴定出 5 个非同义突变，包括 rpoB（H481Y）、dprA（G196C）、femA（F92C）、vraR（E127K）和 agrC（E391stop）。我们进一步研究了 vraR 突变在降低万古霉素敏感性中的作用。将突变的 vraR（E127K）引入万古霉素敏感的金黄色葡萄球菌株中，导致 vraSRmRNA 表达和万古霉素 MIC 的增加，并出现异质 VISA 表型，这通过群体分析谱（PAP）/AUC 得到了证实。电子显微镜显示突变 vraR 的菌株细胞壁厚度增加。
基于基因组数据、分子实验以及 PAP 和细胞壁分析，我们提出 vraR 的单个突变与 MRSA 对万古霉素的敏感性降低以及进一步的治疗失败有关。
