Molecular Epidemiology Laboratory, Tel-Aviv Sourasky Medical Center, Tel-Aviv, Israel; National Laboratory for Antibiotic Resistance and Investigation of Outbreaks in Medical Institutions, National Institute for Antibiotic Resistance and Infection Control, Ministry of Health, Israel.
Molecular Epidemiology Laboratory, Tel-Aviv Sourasky Medical Center, Tel-Aviv, Israel; National Laboratory for Antibiotic Resistance and Investigation of Outbreaks in Medical Institutions, National Institute for Antibiotic Resistance and Infection Control, Ministry of Health, Israel.
Clin Microbiol Infect. 2019 Jun;25(6):711-716. doi: 10.1016/j.cmi.2018.09.014. Epub 2018 Oct 4.
The rise in carbapenem resistance among Gram-negative bacteria has renewed interest in colistin. Recently, the EUCAST-CLSI Polymyxin Breakpoints Working Group declared that broth microdilution (BMD) is the only valid method for colistin susceptibility testing. BMD is not easily incorporated into the routine work of clinical laboratories, and usually this test is incorporated serially, resulting in delayed susceptibility reporting. We tested a strategy of combining VITEK 2 with a 2 μg/mL colistin agar dilution (VITEK 2/AD) screening plate to improve performance and time to reporting of colistin susceptibility.
Colistin susceptibility for 364 clinical isolates was determined by VITEK 2/AD and compared with the reference standard BMD according to the ISO 20776-1:2007 and CLSI guidelines. The EUCAST colistin susceptibility breakpoint of ≤2 μg/mL was used. Escherichia coli NCTC 13846 served as quality control strain. Agreement, very major error (VME) and major error rates were determined using ISO 20776-2:2007.
The VME rate for VITEK 2 alone was 30.6% (15/49, 95% CI 18.3-45.4%), and was reduced to 10.2% (5/49, 95% CI 3.4-22.2%) using the VITEK 2/AD combined testing. The combined testing had categorical agreement with BMD of 97% (354/364, 95% CI 95.0-98.7%), and a major error (ME) rate of 1.6% (5/315, 95% CI 0.5-3.7%). Using the combined testing, even against challenging strains, 349 (95.8%, 95% CI 93.3-97.7%) colistin susceptibility results could be reported, and only 15 isolates required further analysis by BMD.
Our method is simple to apply and allows rapid reporting of colistin susceptibility.
革兰氏阴性菌中碳青霉烯类耐药性的上升重新引起了人们对黏菌素的兴趣。最近，欧盟药敏试验委员会-临床和实验室标准化协会多黏菌素折点工作组宣布肉汤微量稀释法（BMD）是唯一有效的黏菌素药敏检测方法。BMD 不易纳入临床实验室的常规工作中，通常需要连续进行该检测，从而导致药敏报告延迟。我们测试了一种策略，即将 VITEK 2 与 2μg/ml 黏菌素琼脂稀释（VITEK 2/AD）筛选板相结合，以提高黏菌素药敏报告的性能和速度。
使用 VITEK 2/AD 对 364 株临床分离株进行黏菌素药敏试验，并根据 ISO 20776-1：2007 和 CLSI 指南与参考标准 BMD 进行比较。采用 EUCAST 黏菌素药敏折点≤2μg/ml。大肠杆菌 NCTC 13846 作为质控菌株。采用 ISO 20776-2：2007 确定符合率、重大错误率（VME）和主要错误率。
单独使用 VITEK 2 时 VME 率为 30.6%（49 株中的 15 株，95%CI 18.3-45.4%），而使用 VITEK 2/AD 联合检测时则降至 10.2%（49 株中的 5 株，95%CI 3.4-22.2%）。联合检测与 BMD 的分类符合率为 97%（354/364，95%CI 95.0-98.7%），主要错误（ME）率为 1.6%（315 株中的 5 株，95%CI 0.5-3.7%）。使用联合检测方法，即使是针对具有挑战性的菌株，也能报告 349 株（95.8%，95%CI 93.3-97.7%）黏菌素药敏结果，仅 15 株需要进一步用 BMD 进行分析。
我们的方法简单易用，可以快速报告黏菌素药敏结果。
