Background

Repeatedly, too low MIC results were obtained in Bacteroides fragilis quality assessment strains, using gradient strip tests with a ratio of amoxicillin:clavulanic acid of 2:1. We aimed to find the most accurate available gradient strip tests for susceptibility testing of amoxicillin/clavulanic acid in B. fragilis in comparison with agar dilution with EUCAST methodology and breakpoints.

Methods

Twenty-seven clinical B. fragilis isolates were investigated using gold standard EUCAST amoxicillin/clavulanic acid agar dilution (fixed clavulanic acid concentration at 2 mg/L, with increasing amoxicillin concentrations) as well as three commercial gradient strip tests: XL (ratio), AUG (ratio) or AMC (fixed concentration).

Results

Using agar dilution (fixed concentration), 19 isolates were susceptible, 1 isolate was susceptible increased exposure (I) and 7 isolates were resistant. Categorical agreement of the gradient strip tests with agar dilution (fixed concentration) was 70% for XL (ratio), 71% for AUG (ratio) and 89% for AMC (fixed concentration). Very major error rates in comparison with agar dilution (fixed concentration) were 100%, 0%, and 0%, respectively.

Conclusions

EUCAST breakpoint usage in amoxicillin/clavulanic acid susceptibility tests for B. fragilis should be accompanied by EUCAST methodology. When using alternative methods such as gradient strip tests, a higher degree of alignment with EUCAST methodology, such as using fixed clavulanic acid concentrations, improves precision.

中文翻译：

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使用梯度条带测试对脆弱拟杆菌中的阿莫西林/克拉维酸的假敏感性

背景

使用阿莫西林：克拉维酸比例为 2:1 的梯度条带测试，在脆弱拟杆菌质量评估菌株中反复获得过低的 MIC 结果。我们的目标是找到最准确的可用梯度试纸测试，与使用 EUCAST 方法和断点的琼脂稀释相比，用于脆弱拟杆菌中阿莫西林/克拉维酸的敏感性测试。

方法

二十七个临床脆弱拟使用金标准EUCAST阿莫西林/克拉维酸琼脂稀释分离株进行了研究（固定棒酸浓度为2毫克/升，与阿莫西林浓度的增加）以及三个商业梯度条带测试：XL（比率）， AUG（比率）或 AMC（固定浓度）。

结果

使用琼脂稀释（固定浓度），19 株易感，1 株易感，暴露增加 (I)，7 株耐药。琼脂稀释（固定浓度）梯度条带测试的分类一致性为 XL（比率）为 70%，AUG（比率）为 71%，AMC（固定浓度）为 89%。与琼脂稀释（固定浓度）相比，非常大的错误率分别为 100%、0% 和 0%。

结论

在脆弱拟杆菌的阿莫西林/克拉维酸敏感性测试中使用 EUCAST 断点应与 EUCAST 方法一起使用。当使用替代方法（例如梯度条带测试）时，与 EUCAST 方法的更高程度的对齐，例如使用固定的克拉维酸浓度，可以提高精度。