Department of Microbiology & Infectious Diseases, Sydney South West Pathology Service-Liverpool, South Western Sydney Local Health Network, NSW, Sydney, Australia.
J Antimicrob Chemother. 2011 Oct;66(10):2284-7. doi: 10.1093/jac/dkr280. Epub 2011 Jul 12.
To determine the correlation between various vancomycin MIC testing methodologies and explore the phenomenon of MIC creep.
A total of 417 consecutive non-duplicate methicillin-resistant Staphylococcus aureus (MRSA) bloodstream isolates from Liverpool Hospital between 1997 and 2008 were retrieved. All isolates were classified using PFGE and underwent susceptibility testing for vancomycin using a standard Etest (AB bioMérieux, Solna, Sweden), Vitek2(®) (AST-P612; bioMérieux, Inc., Durham, NC, USA) and broth microdilution (BMD) performed as per the CLSI method.
Over the 12 years, 78% (n = 326) of the isolates were multiresistant MRSA (ST239-like by PFGE, where ST stands for sequence type). The correlation between MIC testing methods was moderate with Spearman's correlation coefficients of 0.50 for BMD versus Etest (P < 0.001), 0.33 for BMD versus Vitek2(®) (P < 0.001) and 0.42 for Etest versus Vitek2(®) (P < 0.001). In general, Etest results were 1 dilution higher while the Vitek2(®) results were 1 dilution lower than the BMD MIC result. MIC creep was dependent on the MIC testing method and the measurement used for analysis (geometric mean MIC versus modal MIC versus frequency analysis), with creep detected for Etest regression analysis only. In contrast, the proportion of isolates with a BMD MIC ≥2 mg/L decreased from 16% to 9% in the latter half of the study. Modal MIC was stable over the 12 years at 1 mg/L irrespective of MIC method used.
Correlation between vancomycin MIC methodologies remains suboptimal. Temporal MIC trends should be interpreted with caution as these are dependent on the testing methodology and the measurement used for analysis.
确定各种万古霉素 MIC 检测方法之间的相关性，并探讨 MIC 漂移现象。
从 1997 年至 2008 年，共从利物浦医院收集了 417 例连续的非重复耐甲氧西林金黄色葡萄球菌（MRSA）血流分离株。所有分离株均采用 PFGE 进行分类，并使用标准 Etest（AB bioMérieux，Solna，瑞典）、Vitek2（®）（AST-P612；bioMérieux，Inc.，Durham，NC，美国）和肉汤微量稀释法（BMD）进行万古霉素药敏试验，CLSI 方法进行。
在 12 年期间，78%（n=326）的分离株为多药耐药性 MRSA（PFGE 为 ST239 样，ST 代表序列类型）。MIC 检测方法之间的相关性为中度，Spearman 相关系数分别为 BMD 与 Etest（P<0.001）为 0.50，BMD 与 Vitek2（®）（P<0.001）为 0.33，Etest 与 Vitek2（®）（P<0.001）为 0.42。一般来说，Etest 结果高 1 个稀释度，而 Vitek2（®）结果低 1 个稀释度，与 BMD MIC 结果一致。MIC 漂移取决于 MIC 检测方法和分析使用的测量方法（几何平均值 MIC 与模态 MIC 与频率分析），仅在 Etest 回归分析中检测到 MIC 漂移。相比之下，BMD MIC≥2mg/L 的分离株比例从研究后半段的 16%下降到 9%。模态 MIC 保持稳定，12 年内无论使用何种 MIC 方法，MIC 均为 1mg/L。
万古霉素 MIC 检测方法之间的相关性仍然不理想。MIC 趋势应谨慎解释，因为它们取决于检测方法和分析使用的测量方法。
