Zinc concentrations in cation-adjusted Mueller-Hinton broth (caMHB) from different manufacturers have been found to differ. Here, we evaluated the impact of utilizing different brands and lots of commercially available caMHB on the classification of the antimicrobial susceptibility of metallo-β-lactamase (MBL)-harboring Enterobacteriaceae. We also evaluated the addition of EDTA to caMHB as a means of achieving zinc-limited media. Fifteen clinical Enterobacteriaceae isolates (harboring NDM [n = 7], VIM [n = 3], IMP [n = 2], or KPC [n = 3]) and nine different commercial lots from three caMHB manufacturers (Becton, Dickinson; Oxoid; and Sigma-Aldrich) were utilized. Zinc-limited media were prepared by the addition of EDTA at concentrations ranging from 3 to 300 μg/ml. Meropenem MICs were determined in triplicate for each lot of conventional caMHB and zinc-limited media by broth microdilution. The zinc concentration in each lot of conventional caMHB was determined by inductively coupled plasma mass spectrometry. Up to 8-fold differences in meropenem MICs were observed between the commercial lots, resulting in different classifications of susceptibility among MBL-harboring isolates. Mean zinc concentrations were highest among conventional Becton, Dickinson caMHB lots relative to those for Oxoid and Sigma-Aldrich broth. Among MBL-harboring isolates, the impact of EDTA on MICs was dependent on the lot, correlating with initial zinc availability (i.e., less MIC reduction with higher initial zinc concentrations), while MICs for KPC-harboring isolates were unchanged. In summary, zinc variability was observed among commercial lots of caMHB, resulting in different classifications of susceptibility among MBL-harboring Enterobacteriaceae. The addition of EDTA at concentrations of ≥30 μg/ml was sufficient to provide a zinc-limited medium, resulting in MICs that reflect in vivo meropenem activity.

中文翻译：

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Mueller-Hinton 肉汤品牌之间锌浓度的差异：对产生金属-{β}-内酰胺酶的肠杆菌科细菌药敏试验的影响

已发现来自不同制造商的经阳离子调整的 Mueller-Hinton 肉汤 (caMHB) 中的锌浓度不同。在这里，我们评估了使用不同品牌和大量市售 caMHB 对携带金属β-内酰胺酶 (MBL) 的肠杆菌科细菌的抗菌敏感性分类的影响。我们还评估了将 EDTA 添加到 caMHB 作为实现锌限制培养基的一种手段。15 种临床肠杆菌科分离株（携带 NDM [ n = 7]、VIM [ n = 3]、IMP [ n = 2] 或 KPC [ n= 3]）和来自三个 caMHB 制造商（Becton、Dickinson；Oxoid；和 Sigma-Aldrich）的九个不同商业批次。通过添加浓度范围为 3 至 300 μg/ml 的 EDTA 来制备锌限制培养基。对于每批常规 caMHB 和锌限制培养基，通过肉汤微量稀释一式三份测定美罗培南 MIC。每批常规caMHB中的锌浓度通过电感耦合等离子体质谱法测定。在商业批次之间观察到美罗培南 MIC 的差异高达 8 倍，导致携带 MBL 的分离株之间的易感性分类不同。相对于 Oxoid 和 Sigma-Aldrich 肉汤，传统 Becton、Dickinson caMHB 批次的平均锌浓度最高。在携带 MBL 的分离株中，EDTA 对 MIC 的影响取决于批次，与初始锌可用性相关（即，初始锌浓度较高时 MIC 降低较少），而含有 KPC 的分离株的 MIC 没有变化。总而言之，在商业批次的 caMHB 中观察到锌的变异性，导致 MBL 携带者之间易感性的不同分类肠杆菌科。添加浓度≥30 μg/ml 的 EDTA 足以提供限锌培养基，从而产生反映体内美罗培南活性的MIC 。