Saar Maciej, Wawrzyk Anna, Pastuszak-Lewandoska Dorota, Bielec Filip
Department of Microbiology and Laboratory Medical Immunology, Medical University of Lodz, 90-151 Lodz, Poland.
Department of Basic Biomedical Science, Faculty of Pharmaceutical Sciences in Sosnowiec, Medical University of Silesia, 41-205 Sosnowiec, Poland.
Antibiotics (Basel). 2025 May 21;14(5):527. doi: 10.3390/antibiotics14050527.
Accurate antimicrobial susceptibility testing (AST) of cefiderocol remains a diagnostic challenge, especially in infections caused by metallo-β-lactamase (MBL)-producing . While disk diffusion offers a cost-effective alternative to broth microdilution, it is highly sensitive to factors such as media composition and the presence of atypical colony morphology. The objective of this study was to evaluate how different agar media and interpretations of isolated colonies affect the performance and reliability of cefiderocol AST by disk diffusion. A total of 50 clinical MBL isolates were tested using disk diffusion on Columbia with blood, MacConkey, and chromogenic agars from three manufacturers. Inhibition zones were compared with MICs from broth microdilution. Statistical analyses included paired -tests and Spearman correlation to assess media effects and zone morphology impact. Variability in inhibition zone diameters was observed between media, notably with chromogenic agar. The most consistent results were obtained using Graso Biotech and Thermo Fisher Columbia with blood agar. Isolated colonies were observed in over half the samples and, depending on how they were interpreted, led to major changes in classification accuracy. Up to 64% of results fell into the EUCAST area of technical uncertainty (ATU), and categorical agreement varied across media and interpretive criteria. Disk diffusion for cefiderocol may be used in resource-limited settings but only if rigorously standardized using validated media, consistent zone reading, and ATU-aware interpretive strategies. In borderline cases or when morphological anomalies are present, broth microdilution should be considered the sole reliable method. Clinical microbiologists are advised to exercise caution with ambiguous results and seek expert or confirmatory testing when needed.
对头孢地尔进行准确的药敏试验（AST）仍然是一项诊断挑战，尤其是在由产金属β-内酰胺酶（MBL）的细菌引起的感染中。虽然纸片扩散法为肉汤微量稀释法提供了一种经济有效的替代方法，但它对培养基成分和非典型菌落形态等因素高度敏感。本研究的目的是评估不同的琼脂培养基和对分离菌落的解读如何影响头孢地尔AST纸片扩散法的性能和可靠性。使用来自三个制造商的含血哥伦比亚琼脂、麦康凯琼脂和显色琼脂，通过纸片扩散法对总共50株临床MBL分离株进行了测试。将抑菌圈与肉汤微量稀释法测得的最低抑菌浓度（MIC）进行比较。统计分析包括配对t检验和Spearman相关性分析，以评估培养基的影响和抑菌圈形态的影响。在不同培养基之间观察到抑菌圈直径存在差异，尤其是显色琼脂。使用Graso Biotech公司和赛默飞世尔科技公司的含血哥伦比亚琼脂获得的结果最一致。在超过一半的样本中观察到了分离菌落，根据对它们的解读方式，导致分类准确性发生重大变化。高达64%的结果落入欧洲抗菌药物敏感性试验委员会（EUCAST）的技术不确定性区域（ATU），不同培养基和解读标准下的分类一致性各不相同。头孢地尔的纸片扩散法可用于资源有限的环境，但前提是要使用经过验证的培养基、一致的抑菌圈读数和考虑ATU的解读策略进行严格标准化。在临界病例或存在形态异常的情况下，应将肉汤微量稀释法视为唯一可靠的方法。建议临床微生物学家对不明确的结果保持谨慎，并在需要时寻求专家检测或进行确证性检测。
