Department of Microbiology, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
J Clin Microbiol. 2013 Sep;51(9):2869-74. doi: 10.1128/JCM.00488-13. Epub 2013 Jun 19.
Rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization is crucial for the prevention and control of MRSA infections in health care settings. The LightCycler MRSA Advanced Test (Roche Diagnostics) is a commercially available real-time PCR assay for direct detection of MRSA nasal colonization by targeting of the staphylococcal cassette chromosome mec (SCCmec)-orfX junction. The diagnostic performance of the assay was compared with that of ChromID MRSA agar (bioMérieux) culture and an in-house duplex real-time PCR assay. Among 1,246 nasal swab specimens collected from 2 general hospitals in Hong Kong, 174 (14%) were considered true positive for MRSA. Chromogenic culture and the in-house real-time PCR assay identified 147 (84.5%) and 133 (76.4%) true-positive cases with specificities of 100% and 98.6%, respectively. Based on the target melting temperature (Tm) values (57.0 to 62.0 °C) defined by the manufacturer, the LightCycler MRSA Advanced Test identified only 85 (48.9%) true-positive specimens. Interestingly, an additional 60 (34.5%) true-positive specimens were detected despite atypical Tm values of 55 °C, providing overall sensitivity and specificity values of 83.3% and 99%, respectively. Among isolates with Tm values of 55 °C, most were typed as clonal complex 45 (CC45). By sequence analysis of the SCCmec-orfX junction, characteristic single-nucleotide polymorphisms (SNPs) were identified only in isolates with Tm values of 55°C and not in those with typical Tm values. It is conceivable that those SNPs were located inside the target region of the proprietary hybridization probes, which resulted in a Tm shift in the melting curve analysis. Our study highlights the importance of a global evaluation of commercial kits so that the interpretation algorithm covers different lineages of MRSA clones prevalent in various geographical regions.
快速检测耐甲氧西林金黄色葡萄球菌（MRSA）鼻腔定植对于预防和控制医疗机构中的 MRSA 感染至关重要。LightCycler MRSA 高级检测（罗氏诊断）是一种市售的实时 PCR 检测方法，可通过靶向葡萄球菌盒染色体 mec（SCCmec）-orfX 连接点直接检测 MRSA 鼻腔定植。该检测方法的诊断性能与 ChromID MRSA 琼脂（生物梅里埃）培养和内部实时 PCR 检测方法进行了比较。在香港的 2 家综合医院采集的 1246 份鼻腔拭子标本中，174 份（14%）被认为是 MRSA 的真正阳性。显色培养和内部实时 PCR 检测分别鉴定出 147 份（84.5%）和 133 份（76.4%）真正阳性病例，特异性分别为 100%和 98.6%。根据制造商定义的目标熔解温度（Tm）值（57.0 至 62.0°C），LightCycler MRSA 高级检测仅识别出 85 份（48.9%）真正阳性标本。有趣的是，尽管 Tm 值为 55°C，仍检测到另外 60 份（34.5%）真正阳性标本，总体敏感性和特异性分别为 83.3%和 99%。在 Tm 值为 55°C 的分离株中，大多数为克隆复合体 45（CC45）型。通过 SCCmec-orfX 连接点的序列分析，仅在 Tm 值为 55°C 的分离株中鉴定出特征性单核苷酸多态性（SNP），而在 Tm 值典型的分离株中未鉴定出 SNP。可以想象，这些 SNP 位于专有杂交探针的目标区域内，导致熔解曲线分析中的 Tm 偏移。我们的研究强调了对商业试剂盒进行全面评估的重要性，以便解释算法涵盖在不同地理区域流行的不同 MRSA 克隆谱系。
