Clinical Microbiology Service, Hospital Clínico San Carlos, Madrid, Spain.
Clin Infect Dis. 2010 Mar 15;50(6):821-5. doi: 10.1086/650574.
From April through June 2008, we identified 12 patients in the intensive care unit and 3 patients on other wards infected with methicillin-resistant Staphylococcus aureus that was also resistant to linezolid. We investigated the mechanism of resistance--point mutations in domain V of 23S ribosomal RNA (rRNA) or presence of the cfr gene--involved in the outbreak.
Strains for the study were obtained in the intensive care unit and other wards. Minimal inhibitory concentrations were determined using automated methods, the E-test, or dilution in Mueller-Hinton agar in accordance with Clinical and Laboratory Standards Institute guidelines. Strains were genotyped using pulsed-field gel electrophoresis and were sequenced to determine the presence of point mutations in 23S rRNA. The presence of the cfr gene was determined by specific polymerase chain reaction.
The minimal inhibitory concentrations of linezolid ranged from 16 mg/L to 32 mg/L, and all the strains were susceptible to tigecycline, vancomycin, and daptomycin. Typing of strains sequentially isolated by pulsed-field gel electrophoresis showed that each patient carried only 1 clonal type of linezolid-resistant, methicillin-resistant S. aureus as detected by sequential isolations. The presence of the cfr gene was confirmed in all the isolates. Furthermore, sequencing of domain V of 23S rRNA showed that the most common mechanism of linezolid resistance reported to date, mutation G2576T, was not detected in any of the strains analyzed.
We report the presence of the cfr gene underlying the resistance mechanism involved in a clinical outbreak of linezolid-resistant S. aureus.
2008 年 4 月至 6 月期间，我们在重症监护病房中发现了 12 例耐甲氧西林金黄色葡萄球菌感染病例，且这些菌株对利奈唑胺也具有耐药性；在其他病房中还发现了 3 例耐利奈唑胺的耐甲氧西林金黄色葡萄球菌感染病例。我们对导致此次暴发的耐药机制（核糖体 23S rRNA 结构域 V 中的点突变或 cfr 基因的存在）进行了调查。
从重症监护病房和其他病房中获取了用于研究的菌株。采用自动化方法、E 试验或 Mueller-Hinton 琼脂稀释法按照临床和实验室标准协会（CLSI）的指南来确定最小抑菌浓度。使用脉冲场凝胶电泳对菌株进行基因分型，并对 23S rRNA 进行测序以确定是否存在点突变。通过特异性聚合酶链反应来确定 cfr 基因的存在。
利奈唑胺的最小抑菌浓度范围为 16 mg/L 至 32 mg/L，所有菌株均对替加环素、万古霉素和达托霉素敏感。通过脉冲场凝胶电泳对顺序分离的菌株进行分型表明，每个患者仅携带 1 种克隆类型的利奈唑胺耐药性耐甲氧西林金黄色葡萄球菌，这是通过顺序分离来检测的。所有分离株均证实存在 cfr 基因。此外，对 23S rRNA 结构域 V 的测序表明，在分析的所有菌株中均未检测到迄今为止报道的利奈唑胺耐药的最常见机制，即 G2576T 突变。
我们报告了 cfr 基因的存在，这是导致利奈唑胺耐药性金黄色葡萄球菌临床暴发的耐药机制之一。
