Vestfold Hospital Trust, Department of Microbiology, Tønsberg, Norway; University of Oslo, Institute of Clinical Medicine, Oslo, Norway.
Karolinska University Hospital, Department of Clinical Microbiology, Stockholm, Sweden; Division of Clinical Microbiology, Department of Laboratory Medicine, Karolinska Institutet, Stockholm, Sweden.
Anaerobe. 2023 Jun;81:102743. doi: 10.1016/j.anaerobe.2023.102743. Epub 2023 May 28.
Antimicrobial susceptibility testing (AST) of anaerobic bacteria has until recently been done by MIC methods. We have carried out a multi-centre evaluation of the newly validated EUCAST disk diffusion method for AST of Bacteroides spp.
A panel of 30 Bacteroides strains was assembled based on reference agar dilution MICs, resistance gene detection and quantification of cfiA carbapenemase gene expression. Nordic clinical microbiology laboratories (n = 45) performed disk diffusion on Fastidious Anaerobe Agar with 5% mechanically defibrinated horse blood (FAA-HB) for piperacillin-tazobactam, meropenem and metronidazole.
A total of 43/45 (95.6%) laboratories carried out disk diffusion per protocol. Intraclass correlation coefficients were 0.87 (0.80-0.93) for piperacillin-tazobactam, 0.95 (0.91-0.97) for meropenem and 0.89 (0.83-0.94) for metronidazole. For metronidazole, one media lot yielded smaller zones and higher variability than another. Piperacillin-tazobactam and meropenem zone diameters correlated negatively with cfiA expression. A meropenem zone diameter of <28 mm in B. fragilis indicated presence of cfiA. Piperacillin-tazobactam had the most false susceptible results. Categorical errors for this antimicrobial were particularly prevalent in cfiA-positive strains, and piperacillin-tazobactam had the highest number of comments describing zone reading difficulties.
Inter-laboratory agreement by disk diffusion was good or very good. The main challenges were media-related variability for metronidazole and categorical disagreement with the reference method for piperacillin-tazobactam in some cfiA-positive strains. An area of technical uncertainty specific for such strains may be warranted.
直到最近，厌氧菌的药敏试验（AST）都是通过 MIC 方法进行的。我们对新验证的 EUCAST 纸片扩散法进行了多中心评估，用于检测拟杆菌属的 AST。
根据参考琼脂稀释 MIC、耐药基因检测和 cfiA 碳青霉烯酶基因表达定量，组装了 30 株拟杆菌属菌株的小组。北欧临床微生物学实验室（n=45）在含有 5%机械纤维分解马血的艰难梭菌琼脂（FAA-HB）上进行哌拉西林-他唑巴坦、美罗培南和甲硝唑的纸片扩散试验。
共有 43/45（95.6%）实验室按方案进行了纸片扩散。哌拉西林-他唑巴坦的组内相关系数为 0.87（0.80-0.93），美罗培南为 0.95（0.91-0.97），甲硝唑为 0.89（0.83-0.94）。对于甲硝唑，一个培养基批次的结果比另一个更小，且变异性更高。哌拉西林-他唑巴坦和美罗培南的抑菌圈直径与 cfiA 表达呈负相关。在脆弱拟杆菌中，美罗培南抑菌圈直径<28mm 表明存在 cfiA。哌拉西林-他唑巴坦有最多的假敏感结果。这种抗菌药物的分类错误在 cfiA 阳性菌株中尤其普遍，哌拉西林-他唑巴坦有最多的描述抑菌圈读数困难的评论。
纸片扩散的实验室间一致性良好或非常好。主要挑战是甲硝唑的培养基相关变异性以及在一些 cfiA 阳性菌株中与参考方法的分类不一致。可能需要针对此类菌株的特定技术不确定性领域。
