Papadimitriou-Olivgeris M, Filippidou S, Kolonitsiou F, Drougka E, Koutsileou K, Fligou F, Dodou V, Sarrou S, Marangos M, Vantarakis A, Anastassiou E D, Petinaki E, Spiliopoulou I
Division of Infectious Diseases, School of Medicine, University of Patras, Patras, Greece.
Environmental Microbiology Unit, Department of Hygiene, School of Medicine, University of Patras, Patras, Greece.
Lett Appl Microbiol. 2016 Sep;63(3):189-95. doi: 10.1111/lam.12610. Epub 2016 Aug 5.
The aims were to assess the performance of Vitek 2 in identifying enterococcal species and the implementation of GeneXpert(®) vanA/vanB PCR for the detection of vancomycin-resistant enterococci (VRE). Gram-positive cocci from clinical and environmental specimens (n = 431) suspicious of being enterococci by conventional methods were evaluated by Vitek 2. This system identified 296 Enterococcus faecium, 87 Enterococcus faecalis, 10 Enterococcus villorum, 9 Enterococcus gallinarum, 9 Enterococcus durans, 5 Enterococcus casseliflavus, 1 Enterococcus spp. and 14 isolates as Non-Enterococcus. All strains were submitted to pulsed field gel electrophoresis (PFGE) analysis showing 64 banding patterns. Representative strains from each banding pattern were further characterized to species level by 16S rDNA sequencing. The misidentification rate by Vitek 2 to species level among 429 molecularly identified enterococci was 6% (26 isolates). Additionally, 372 rectal swabs were obtained from critically ill patients. They were evaluated for the presence of VRE by ChromID VRE combined with in-house PCR vs GeneXpert(®) . GeneXpert(®) showed high (>92%) sensitivity, specificity, accuracy for vanA-positive Enterococcus detection, as well as, sensitivity and specificity for vanB-positive strains. Positive predictive value for detection of vanB-positive enterococci by GeneXpert(®) vanA/vanB was low (30%). GeneXpert(®) showed the same efficacy as ChromID VRE in detecting vanA-positive enterococci, but lower for vanB-gene detection.
The study shows that even though the performance of Vitek 2 Advanced Expert System was good in identifying enterococci to species level, it is important to verify results by a molecular method when phenotypic findings are discordant with epidemiologic patterns. Furthermore, GeneXpert(®) vanA/vanB PCR and ChromID VRE combined with in-house PCR were applied in rectal samples for the detection of VRE colonization among critically ill patients. GeneXpert(®) showed an excellent performance in detecting vanA-positive enterococci, but false-positive results for vanB-gene detection render its application problematic in departments with high incidence of vanB-positive enterococci.
本研究旨在评估Vitek 2系统在鉴定肠球菌属菌种方面的性能，以及评估GeneXpert(®) vanA/vanB聚合酶链反应（PCR）在检测耐万古霉素肠球菌（VRE）中的应用。通过Vitek 2系统对来自临床和环境标本（n = 431）的革兰氏阳性球菌进行评估，这些标本通过传统方法怀疑为肠球菌。该系统鉴定出296株屎肠球菌、87株粪肠球菌、10株鹑鸡肠球菌、9株鹑肠球菌、9株耐久肠球菌、5株卡氏黄色肠球菌、1株未明确的肠球菌属菌株以及14株非肠球菌分离株。所有菌株均进行脉冲场凝胶电泳（PFGE）分析，显示出64种条带模式。通过16S核糖体DNA（rDNA）测序对每种条带模式的代表性菌株进一步鉴定到菌种水平。在429株经分子鉴定的肠球菌中，Vitek 2系统在菌种水平的错误鉴定率为6%（26株分离株）。此外，从重症患者中获取了372份直肠拭子。通过ChromID VRE培养基结合内部PCR与GeneXpert(®)对其进行VRE检测评估。GeneXpert(®)在检测vanA阳性肠球菌方面显示出高（>92%）的敏感性、特异性和准确性，对vanB阳性菌株也具有敏感性和特异性。GeneXpert(®) vanA/vanB检测vanB阳性肠球菌的阳性预测值较低（30%）。GeneXpert(®)在检测vanA阳性肠球菌方面与ChromID VRE培养基具有相同的效能，但在检测vanB基因方面效能较低。
该研究表明，尽管Vitek 2高级专家系统在将肠球菌鉴定到菌种水平方面表现良好，但当表型结果与流行病学模式不一致时，通过分子方法验证结果很重要。此外，将GeneXpert(®) vanA/vanB PCR和ChromID VRE培养基结合内部PCR应用于直肠样本，以检测重症患者中的VRE定植情况。GeneXpert(®)在检测vanA阳性肠球菌方面表现出色，但vanB基因检测的假阳性结果使其在vanB阳性肠球菌高发科室的应用存在问题。
