State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, National Clinical Research Center for Infectious Diseases, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China.
Institution of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden.
Lett Appl Microbiol. 2021 Aug;73(2):197-205. doi: 10.1111/lam.13492. Epub 2021 Jun 9.
Antimicrobial susceptibility testing with the last-resort antibiotics polymyxins (polymyxin B and colistin) is associated with several methodological issues. Currently, broth microdilution (BMD) is recommended for colistin and polymyxin B. BMD is laborious and the utility of alternative methods needs to be evaluated for polymyxin B susceptibility testing. In this study, using BMD as a reference method, the performance of agar dilution (AD) and MIC test strips (MTS) were evaluated in polymyxin B susceptibility testing. BMD, AD and MTS were used to determine MICs of 193 clinical isolates of Escherichia coli. Seventy-nine were positive for the polymyxin resistance gene mcr-1. Method performances were evaluated based on pair-wise agreements with the reference method (BMD) and statistical testing. AD and MTS showed an unacceptable number of very major errors (VMEs) compared with BMD, 9·3 and 10·7%, respectively. The essential agreement (EA) was low for AD (49·7%), but high for MTS (97·8%). However, statistical testing showed that MTS tended to yield a one-step lower MIC (P < 0·01) compared with BMD. The discordances observed with MTS and AD in comparison with BMD for polymyxin B susceptibility testing for E. coli suggest their inapplicability in routine testing. A large number of isolates clustered around the susceptibility breakpoint (2-4 mg l ) and several mcr-1 positive isolates (17%) were determined as susceptible with BMD. A screening breakpoint for mcr-1 of 2 mg l should also be considered.
抗微生物药物敏感性试验采用最后一线抗生素多黏菌素（多黏菌素 B 和黏菌素），与若干方法学问题相关。目前，黏菌素和多黏菌素 B 推荐使用肉汤微量稀释法（BMD）。BMD 较为繁琐，需要评估替代方法在多黏菌素 B 药敏试验中的应用。本研究采用 BMD 作为参考方法，评估琼脂稀释法（AD）和微量肉汤稀释法药敏试验条（MTS）在多黏菌素 B 药敏试验中的表现。BMD、AD 和 MTS 用于测定 193 株大肠埃希菌临床分离株的 MIC。79 株为多黏菌素耐药基因 mcr-1 阳性。基于与参考方法（BMD）的一致性和统计学检验评估方法性能。与 BMD 相比，AD 和 MTS 出现大量不可接受的重大错误（VME），分别为 9.3%和 10.7%。AD 的一致性（EA）较低（49.7%），而 MTS 较高（97.8%）。然而，统计学检验表明，与 BMD 相比，MTS 倾向于产生一步更低的 MIC（P<0.01）。与 BMD 相比，MTS 和 AD 在多黏菌素 B 药敏试验中对大肠埃希菌的一致性较差，提示它们不适用于常规检测。大量分离株聚集在药敏分界点（2-4 mg/L）附近，17%的 mcr-1 阳性分离株被 BMD 判定为敏感。mcr-1 的筛选分界点也应考虑为 2 mg/L。
