对唑类药物交叉耐药的烟曲霉临床分离株耐药机制的初步探讨

Molecular mechanisms of cross-resistance to azole antifungal agents in a clinical isolate of Aspergillus fumigatus： a preliminary study

目的 研究对唑类药物交叉耐药的烟曲霉临床分离株的耐药机制.方法 自1例侵袭性曲霉病患者体内分离得到1株烟曲霉,分别利用美国临床实验室标准化研究所（CLSI）M38-A2中的微量液基稀释法和E-test法测定伊曲康唑、伏立康唑、两性霉素B、泊沙康唑和卡泊芬净对该烟曲霉的最低抑菌浓度（MIC）/最低有效浓度（MEC）;并对该菌株中唑类药物靶酶基因cyp51A进行克隆和序列测定分析.结果 微量液基稀释法显示,该菌株伊曲康唑、伏立康唑、两性霉素B的MIC分别为≥16、8、1mg/L,卡泊芬净的MEC为0.5 mg/L.E-test法显示,伊曲康唑、伏立康唑、两性霉素B和泊沙康唑的MIC分别为≥32、≥32、12和≥32 mg/L,卡泊芬净的MIC为0.047 mg/L.对cyp51A基因进行测序并分析后发现,该菌株的cyp51A序列中存在启动子区-288到-322位间34 bp的串联序列的插入,以及该基因编码区364位碱基的点突变（T364A）,导致了编码区98位亮氨酸的置换（L98H）;该菌株的cyp51A基因编码区还存在137位碱基（A137T）、585位碱基（G585A）、814位碱基（C814A）、836位碱基（G836C）、991位碱基（T991C）、1350位碱基（A1350G）的突变,并分别导致编码区相应氨基酸的置换.结论 分离到对唑类药物交叉耐药的烟曲霉临床株,该菌株的cyp51A基因存在启动子区34 bp的串联序列插入和编码区364位的突变（T364A）,这种变化参与了其对伊曲康唑、伏立康唑和泊沙康唑交叉耐药;该菌株cyp51A基因编码区还存在一些其他的点突变,并可导致相应部位的氨基酸置换.

Objective To investigate the molecular mechanisms of cross-resistance to azoles in a clinical isolate of Aspergillus fumigatus. Methods A. fumigatus was isolated from a patient with invasive aspergillosis.Clinical Laboratory Standard Institute M38-A2 broth microdilution method and E-test method were used to determine the minimum inhibitory concentrations （MICs） or minimum effective concentration （MEC） of itraconazole, voriconazole, amphotericin B, posaconazole and caspofungin for the A. fumigatus isolate. DNA was extracted from the isolate and subjected to the amplification of cyp51A gene encoding the target enzyme of azole antifungal agents followed by sequence analysis. Results The broth microdilution test showed that the MEC of caspofungin was 0.5 mg/L, and MICs of itraconazole, voriconazole and amphotericin B were ≥ 16 mg/L,8 mg/L and 1 mg/L, respectively, for this isolate; while E-test assay revealed that the MICs of caspofungin,itraconazole, voriconazole, amphotericin B and posaconazole were 0.047 mg/L, ≥32 mg/L,≥32 mg/L, 12 mg/L and ≥32 mg/L, respectively. Sequence analysis showed an insertion of a 34-bp tandem sequence in the promoter region of the cyp51A gene as well as a T364A point mutation causing the substitution of leucine 98 （L98H）. In addition, there were some other mutations in the cyp51A gene of this isolate, such as A137T,G585A, C814A, G836C, T991C and A1350G, which could result in corresponding amino acid substitutions.Conclusions An A. fumigatus strain with cross-resistance to azole antifungal agents is isolated. There is an insertion of a 34-bp tandem sequence into the promoter region as well as a T364A point mutation in the cyp51A gene, which contribute to the cross resistance to azole antifungal agents including itraconazole, voriconazole,and posaconazole. In addition, other mutations causing amino acid substitutions have also been detected in the cyp51 A gene of this isolate.