金黃色葡萄球菌之基因型與表現型相關性研究

前言：金黃色葡萄球菌(Staphylococcus aureus) 是造成多種感染之主要細菌之一。根據其對抗生素之敏感度可分為MSSA及MRSA。其中MRSA感染可分兩類：醫院型MRSA和社區型MRSA。雖兩者皆有可移動的mecA基因，可造成對β-lactam (內醯胺)類抗生素具耐藥性，但兩者卻具有相異臨床表現及分子特徵。目的：本研究目的是分析臺灣中部一醫學中心之MRSA分子流行病學特徵表現型(phenotype)和基因型(genotype)相關性並比較各式偵測MRSA工具之良窳。方法：所有菌株之抗生素最低抑菌濃度(MIC) 藥物敏感試驗皆采瓊脂稀釋法(agar dilution method，根據CLSI標準)偵測。MRSA基因鑑定係以DNA為模板，藉由多重PCR (Multiplex-PCR)測定SCCmec中 ccr和 mec基因複合體之分型。結果：本研究發現所有MRSA菌株中對oxacillin與cefoxitin呈抗藥性分別占63.6% (152/239株)與98.7% (236/239株)。此研究結果顯示cefoxitin 較 oxacillin更能精準偵測 MRSA，這與 CLSI的建議相互對應。藉由M-PCR發現SCCmec type I、II、 III、IV、V 和 VT 分別占0%、5.9%、35.6%、32.2%、7.1% 和19.2%。醫院型 (type I、II、III) 及社區型 (type IV、V、VT) MRSA菌株分別占41.4%及58.6%。 另外本研究發現HA-MRSA抗藥性並不受 2% NaCl 影響，與2% NaCl對CA-MRSA的反應有明顯不同。結論：經由本研究可發現金黃色葡萄球菌抗藥性的基因型與表現型之相關性，而藉由分子生物學的基因型偵測可彌補臨床微生物實驗室偵測常規藥物敏感性的不足之處。另外亦發現含有2% NaCl的oxacillin具有快速區分醫院型MRSA及社區型MRSA的潛力，本研究結果可供未來基礎及臨床研究作為參考。

Staphylococcus aureus is one of the main causes of various infections. According to their susceptibility to antibiotics, we can classify them into two categories: MSSA and MRSA. MRSA infection can be further divided into two groups: HA-MRSA (hospital-acquired MRSA) and CA-MRSA (community-acquired MRSA). Although both of them harbored mobile mecA gene, which lead to the resistance of β-lactam antibiotics, they have different clinical performances and molecular characteristics in each other. The goal of this study is to analyze the relationship between epidemiological phenotype and genotype of MRSA. We also compare several methods of MRSA detection whether is useful or not. All of isolates’ Minimum inhibitory concentrations (MICs) of antibiotics were determined by agar dilution method according to the Clinical and Laboratory Standards Institute (CLSI). Genomic of MRSA was used DNA as templates and the types of cassette chromosome recombinase (ccr) complex and mecA gene complexes (SCCmec) were determined by multiplex PCR (M-PCR). Our result indicated that 63.6% (152/239) of all MRSA isolates were oxacillin- resistant MRSA; 98.7% (236/239) of them were cefoxitin-resistant MRSA. This result demonstrated that use cefoxitin as MRSA detection method is more accurate than oxacillin in detecting MRSA. It corresponded to suggestion of CLSI. We found that SCCmec type I, II, III, IV, V and VT were 0%, 5.9%, 35.6%, 32.2%, 7.1% and 19.2% via M-PCR respectively. HA-MRSA (I, II and III) and CA-MRSA (IV, V and VT) isolates were 41.4% and 58.6% respectively. In addition, we found that resistance of HA-MRSA is not affected by 2% NaCl, while CA-MRSA is affected by 2% NaCl. This study showed that the relationship between genotypic and phenotypic characteristics of MRSA isolates. Molecular method can make up the limitation of clinical microbiology laboratory ability. In addition, we found that oxacillin with 2% NaCl added have potential on identification between HA-MRSA and CA-MRSA rapidly, our studies can be used for reference on future basic or clinical studies