采用分子诊断检测阳性血培养中耐甲氧西林金黄色葡萄球菌的性能：mecA 阳性细菌共存及耐甲氧西林金黄色葡萄球菌中 orfX-SCCmec 连接区多样性对其的影响。
Detecting the performance of methicillin-resistant Staphylococcus aureus by a molecular diagnostic assay in positive blood culture: Influence of coexistence of mecA-positive bacteria and diversity in orfX-SCCmec junction region in methicillin-susceptible S. aureus.
机构信息
Division of Laboratory Medicine, Sapporo Medical University Hospital, Sapporo, Japan.
Department of Hygiene, Sapporo Medical University School of Medicine, Sapporo, Japan.
出版信息
J Infect Chemother. 2023 Sep;29(9):838-842. doi: 10.1016/j.jiac.2023.05.006. Epub 2023 May 12.
BACKGROUND
In blood cultures that test positive for staphylococcal bacteria, rapid identification of methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-susceptible Staphylococcus aureus (MSSA) by molecular assay is useful for appropriate antimicrobial treatment of bloodstream infections. Although the Xpert MRSA/SA BC assay is widely available in clinical settings in Japan, its efficacy has not yet evaluated thoroughly.
METHODS
We retrospectively studied 100 blood culture cases positive for S. aureus at Sapporo Medical University Hospital between March 2019 and May 2022. Cycle threshold (CT) values for target genes from the Xpert MRSA/SA BC assay were compared to phenotypic results. Genotyping and genetic analysis of the orfX-SCCmec junction region was performed for selected isolates.
RESULTS
We analyzed 25 and 75 isolates assigned to MRSA and MSSA, respectively, using the Xpert MRSA/SA BC assay. Of these, 99 isolates from agar cultures showed compatible susceptibility to oxacillin. One genetically misidentified case of MRSA was found to be caused by the mixed growth of MSSA and methicillin-resistant S. hominis on agar culture. Of the 73 MSSA with pure growth on agar culture, 45 (61.6%) were found to be orfX-SCCmec-positive, spa-positive, and mecA-negative in this assay. These MSSA belong to diverse spa and coa types.
CONCLUSION
The Xpert MRSA/SA BC assay accurately identified MRSA and MSSA in positive blood cultures. However, over half of the MSSA isolates showed positive results for orfX-SCCmec, presumably due to genetic diversity in the orfX-associated region of MSSA. Therefore, the coexistence of MSSA and mecA-harboring coagulase-negative staphylococci may cause confusion about identification of MRSA.
背景
在血培养物中检测到葡萄球菌呈阳性时，通过分子检测快速鉴定耐甲氧西林金黄色葡萄球菌（MRSA）或甲氧西林敏感金黄色葡萄球菌（MSSA），有助于对血流感染进行适当的抗菌治疗。虽然 Xpert MRSA/SA BC 检测在日本的临床环境中广泛应用，但尚未对其疗效进行全面评估。
方法
我们回顾性研究了 2019 年 3 月至 2022 年 5 月在札幌医科大学医院检测到金黄色葡萄球菌呈阳性的 100 例血培养病例。比较 Xpert MRSA/SA BC 检测靶基因的 CT 值与表型结果。对选定的分离株进行 orfX-SCCmec 连接区的基因分型和遗传分析。
结果
我们使用 Xpert MRSA/SA BC 检测分析了 25 株和 75 株分别被分配为 MRSA 和 MSSA 的分离株。其中，来自琼脂培养物的 99 株分离株对苯唑西林显示出相容的药敏性。发现一个基因上被错误鉴定为 MRSA 的分离株是由于在琼脂培养物上混合生长的 MSSA 和耐甲氧西林的人葡萄球菌。在 73 株在琼脂培养物上纯培养的 MSSA 中，有 45 株（61.6%）在该检测中被鉴定为 orfX-SCCmec 阳性、spa 阳性和 mecA 阴性。这些 MSSA 属于不同的 spa 和 coa 型。
结论
Xpert MRSA/SA BC 检测在阳性血培养物中准确地鉴定了 MRSA 和 MSSA。然而，超过一半的 MSSA 分离株在 orfX-SCCmec 检测中呈阳性结果，推测这是由于 MSSA 中 orfX 相关区域的遗传多样性所致。因此，MSSA 与携带 mecA 的凝固酶阴性葡萄球菌共存可能会导致对 MRSA 鉴定的混淆。
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