cfxA 抗藥性基因在Bacteroides 和Prevotella
菌種之分子遺傳特性研究

從台灣南部之醫院共收集148 株Bacteroides 和Prevotella 為試驗菌株。用以探討cfxA 抗藥基因之分子生物特性。我們自行設計一對具有特異性之引子(primer cfx- Ⅰ，primer cfx -Ⅱ) 操作聚合.連鎖反應(PCR)。篩選出28 株具有cfxA 基因的試驗菌株。再選用另一對特異性之引子(primer cfx- Ⅲ，primer cfx- Ⅳ)藉由聚合. 連鎖反應放大得到完整的cfxA 基因。結果得到cfxA2 基因(19 株)；cfxA3 基因(7 株)。另外有2 株序列是全新的cfxA3-like 基因。所有這些定序分析, 我們重複測定二次所得相同之結果。同時，我們以B. fragilis bf040 和B. distasonis bd106 這兩株cfxA3-like 基因之聚合.連鎖反應產物作基因選殖，形質轉入勝任細胞( competent cell )E. coli XL1-blue，並測定其對各種抗生素之敏感試驗。結果cefoxitin MIC=12 μg/ml 轉變為MIC= 24 μg/ml。2 株含有全新之序列的菌株，其變異位置分別是B. fragilis bf040 在核.酸序列775 位置為t→a 變異，即胺基酸序列N239Y 變異，再加上其核.酸序列886 位置為a→g 變異，即胺基酸序列E272K 變異，於是我們將它命名為新型cfx A3-like-1 基因。另一株，B.distasonis bd106 則是在核.酸序列776 位置為a→g 變異，即胺基酸C239Y 變異。以及核.酸序列886 位置為a→g 變異，即胺基酸序列E272K 變異，於是我們將它命名為cfx A3-like-2 基因。對此核.酸序列之改變是否與cfxA 基因對藥物抗藥性表現有關，值得我們再進一步分析探討。

關鍵字

Bacteroides ； cfxA抗藥基因； PCR ； Prevotella

並列摘要

A total of obtained 148 strains of Bacteroides species and Prevotella species, from Kaohsiung Medical University Chung-Ho Memorial Hospital, were used for study of cfxA gene. A pair of specific primers (primer cfx-I and primer cfx-II) were designed and used for PCR reaction. A total of 28 tested strains were found to harbor cfxA gene. These strains were furthermore submitted to PCR reaction using another specific primer pairs (primer cfx-III, primer cfx-IV) to amplify the entire cfxA gene. From the sequence analysis, the results showed that 19 isolates of tested strains were positive for cfxA2, 7 strains were positive for cfxA3. However, the sequences of the other two tested strains contained the novel gene. All the sequence analysis was repeated twice to confirm the results. The PCR products from B. fragilis bf040 and B. distasonis bd.106 were used for PCR cloning and then transform into competent cells, E. coli XL1-blue. From drug susceptibility testing, the results revealed that the transformant cells of E. coli XL1-blue changed from sensitive to resistant to cefoxitin. Two strains of Bacteroides species with a novel gene were isolated in this study. B. fragilis bf040 had a N239Y and an E272K substitution, so it was named cfxA3-like-1 gene. Also, B. distasonisbd106 had a C239Y and an E272K substitution, so it was also named cfxA3-like-2 gene. The role of cfxA gene has not been completely clarified, and more studies are needed to understand its role in antimicrobial resistance.