Institute of Medical Microbiology, University Hospital Münster, Münster, Germany.
Robert-Koch-Institute, Berlin, Germany.
J Clin Microbiol. 2017 Dec 26;56(1). doi: 10.1128/JCM.00826-17. Print 2018 Jan.
Similar to , confers resistance against beta-lactams, leading to the phenotype of methicillin-resistant (MRSA). However, -harboring MRSA strains pose special difficulties in their detection. The aim of this study was to assess and compare different phenotypic systems for screening, identification, and susceptibility testing of -positive MRSA isolates. A well-characterized collection of -positive isolates ( = 111) was used for evaluation. Routinely used approaches were studied to determine their suitability to correctly identify -harboring MRSA, including three (semi)automated antimicrobial susceptibility testing (AST) systems and five selective chromogenic agar plates. Additionally, a cefoxitin disk diffusion test and an oxacillin broth microdilution assay were examined. All -harboring MRSA isolates were able to grow on all chromogenic MRSA screening plates tested. Detection of these isolates in AST systems based on cefoxitin and/or oxacillin testing yielded overall positive agreements with the genotype of 97.3% (MicroScan WalkAway; Siemens), 91.9% (Vitek 2; bioMérieux), and 64.9% (Phoenix, BD). The phenotypic resistance pattern most frequently observed by AST devices was "cefoxitin resistance/oxacillin susceptibility," ranging from 54.1% (Phoenix) and 83.8% (Vitek 2) to 92.8% (WalkAway). The cefoxitin disk diffusion and oxacillin broth microdilution assays categorized 100% and 61.3% of isolates to be MRSA, respectively. The chromogenic media tested confirmed their suitability to reliably screen for -harboring MRSA. The AST systems showed false-negative results with varying numbers, misidentifying -harboring MRSA as methicillin-susceptible This study underlines cefoxitin's status as the superior surrogate -positive MRSA marker.
类似于 ， 赋予了对β-内酰胺类药物的抗性，导致耐甲氧西林金黄色葡萄球菌（MRSA）的表型。然而，携带 基因的 MRSA 菌株在检测方面带来了特殊的困难。本研究旨在评估和比较不同的表型系统，用于筛选、鉴定和药敏试验 阳性的 MRSA 分离株。使用经过充分特征描述的 阳性 分离株（n=111）进行评估。研究了常规使用的方法，以确定它们是否适合正确识别携带 基因的 MRSA，包括三种（半）自动化抗菌药物敏感性测试（AST）系统和五种选择性显色琼脂平板。此外，还检查了头孢西丁纸片扩散试验和苯唑西林肉汤微量稀释法。所有携带 基因的 MRSA 分离株都能够在所有测试的显色性 MRSA 筛选平板上生长。基于头孢西丁和/或苯唑西林检测的 AST 系统检测这些分离株，与 基因的总体阳性符合率为 97.3%（MicroScan WalkAway；西门子）、91.9%（Vitek 2；生物梅里埃）和 64.9%（Phoenix，BD）。AST 设备最常观察到的表型耐药模式是“头孢西丁耐药/苯唑西林敏感”，范围从 54.1%（Phoenix）和 83.8%（Vitek 2）到 92.8%（WalkAway）。头孢西丁纸片扩散试验和苯唑西林肉汤微量稀释法分别将 100%和 61.3%的分离株归类为 MRSA。测试的显色培养基证实了它们可靠筛选携带 基因的 MRSA 的适用性。AST 系统显示出不同数量的假阴性结果，错误地将携带 基因的 MRSA 鉴定为耐甲氧西林敏感的 。本研究强调了头孢西丁作为替代 阳性 MRSA 标志物的优势地位。
