Department of Pharmacy Services, Hartford Hospital, Hartford, Connecticut, USA.
Center for Anti-Infective Research and Development, Hartford Hospital, Hartford, Connecticut, USA.
J Clin Microbiol. 2020 Nov 18;58(12). doi: 10.1128/JCM.02019-20.
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 We also evaluated the addition of EDTA to caMHB as a means of achieving zinc-limited media. Fifteen clinical isolates (harboring NDM [ = 7], VIM [ = 3], IMP [ = 2], or KPC [ = 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 The addition of EDTA at concentrations of ≥30 μg/ml was sufficient to provide a zinc-limited medium, resulting in MICs that reflect meropenem activity.
不同制造商生产的阳离子调整 Mueller-Hinton 肉汤（caMHB）中的锌浓度有所不同。在此，我们评估了使用不同品牌和批次的市售 caMHB 对金属β-内酰胺酶（MBL）携带物抗菌药敏分类的影响。我们还评估了在 caMHB 中添加 EDTA 作为实现锌限制培养基的方法。我们使用了 15 株临床分离株（携带 NDM [ = 7]、VIM [ = 3]、IMP [ = 2] 或 KPC [ = 3]）和来自 3 个 caMHB 制造商（BD、Oxoid 和 Sigma-Aldrich）的 9 个不同的商业批次。通过添加 3 至 300μg/ml 浓度的 EDTA 来制备锌限制培养基。通过肉汤微量稀释法，对每个 caMHB 批次的常规 caMHB 和锌限制培养基重复进行 3 次美罗培南 MIC 测定。通过电感耦合等离子体质谱法测定每个常规 caMHB 批次的锌浓度。在商业批次之间观察到美罗培南 MIC 高达 8 倍的差异，导致 MBL 携带分离株的药敏分类不同。与 Oxoid 和 Sigma-Aldrich 肉汤相比，BD 的常规 caMHB 批次的平均锌浓度最高。在 MBL 携带分离株中，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 减少较少），而 KPC 携带分离株的 MIC 不变。总之，在 caMHB 的商业批次中观察到锌的可变性，导致 MBL 携带分离株的药敏分类不同。添加浓度≥30μg/ml 的 EDTA 足以提供锌限制培养基，从而使 MIC 反映美罗培南的活性。
