Clinical isolates of Escherichia coli (n = 554) were tested against fosfomycin using agar dilution, disk diffusion, and Etest. Agar dilution (reference method) identified few isolates with fosfomycin MICs of 64 (n = 3), 128 (n = 4), and ≥256 μg/ml (n = 2). Applying CLSI (M100, 2020) and EUCAST (v. 10.0, 2020) breakpoints, 98.9% and 98.4% (agar dilution), 99.3% and 99.1% (disk diffusion), and 99.1% and 98.9% (Etest) of isolates were fosfomycin susceptible, respectively. Essential agreement (agar dilution versus Etest) was low (40.8%); 59.3% (131/221) of isolates with agar dilution MICs of 2 to 128 μg/ml tested 2 to 4 doubling dilutions lower by Etest. Applying CLSI breakpoints, categorical agreement was >99% for both disk diffusion and Etest; no major errors (MEs) or very major errors (VMEs) were identified, and rates of minor errors (mEs) were <1%. EUCAST breakpoints yielded categorical agreements of >99% and no MEs for both disk diffusion and Etest; however, VMEs occurred at unacceptable rates of 44.4% (disk diffusion) and 33.3% (Etest). All isolates with agar dilution MICs of ≥32 μg/ml (n = 12) and a subset of isolates with MICs of ≤16 μg/ml (n = 49) were also tested using the Vitek 2 AST-N391 card and generated fosfomycin MICs 1 to ≥3 doubling dilutions lower than agar dilution for 11/12 isolates with agar dilution MICs of ≥32 μg/ml. We conclude that performing fosfomycin disk diffusion or Etest on urinary isolates of E. coli and interpreting results using CLSI breakpoints reliably identified fosfomycin-susceptible isolates regardless of differences in endpoint reading criteria. EUCAST breakpoints generated excessive rates of VMEs for our isolate collection of high fosfomycin susceptibility.

中文翻译：

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通过四种体外测试方法测量的大肠杆菌临床分离株对磷霉素的敏感性。

使用琼脂稀释，圆盘扩散和Etest对大肠杆菌的临床分离株（n = 554）进行了针对磷霉素的测试。琼脂稀释（参考方法）鉴定出的磷霉素MIC分别为64（n = 3），128（n = 4）和≥256μg/ ml（n= 2）。应用CLSI（M100，2020）和EUCAST（v。10.0，2020）断点的分离株分别为98.9％和98.4％（琼脂稀释），99.3％和99.1％（磁盘扩散）以及99.1％和98.9％（Etest）分离株磷霉素易感。基本一致性（琼脂稀释与Etest相比）低（40.8％）；琼脂稀释MIC为2至128μg/ ml的分离株的59.3％（131/221）进行了Etest测试，其琼脂稀释MIC降低了2-4倍。应用CLSI断点，磁盘扩散和Etest的分类一致性均大于99％；没有发现重大错误（ME）或非常重大错误（VME），次要错误率（mE）小于1％。EUCAST断点产生的分类一致性大于99％，并且没有磁盘扩散和Etest的ME。但是，VME的发生率不可接受，分别为44.4％（磁盘扩散）和33.3％（Etest）。n = 12）和MIC≤16μg/ ml（n = 49）的分离株的子集也使用Vitek 2 AST-N391卡进行了测试，生成的磷霉素MIC为1或≥3倍，比琼脂稀释倍数低11 / 12个琼脂稀释MIC≥32μg/ ml的分离株。我们得出的结论是，对大肠杆菌的尿分离株进行磷霉素圆盘扩散或Etest并使用CLSI断点解释结果可可靠地鉴定出对磷霉素敏感的分离株，而与终点阅读标准的差异无关。EUCAST断点为我们分离出的高磷霉素易感性菌株产生了过量的VME。