结核分枝杆菌利福平分子药敏结果与其表型药敏差异的研究

目的 分析结核分枝杆菌利福平耐药的分子药敏(Xpert MTB/RIF)检测与在表型药敏(Bactec MGIT 960)检测结果不一致的机制。 方法 从2015年10月－2018年4月在长沙医学院第一附属医院进行 Xpert MTB/RIF 检测的8 274位患者中筛选出 Xpert MTB/RIF 检测利福平耐药而 Bactec MGIT 960 利福平敏感的患者39例,以及Xpert MTB/RIF 检测利福平敏感而 Bactec MGIT 960 利福平耐药的患者7例,共46例患者标本复苏其分离株,然后提取基因组DNA并进行rpoB的利福平耐药决定区域(rifampicin resistance determining region, RRDR)测序,同时对所有复苏的分离株进行最低抑菌浓度(minimum inhibitory concentration, MIC)测定,观察不同突变菌株的耐药程度。 结果 46例患者中有2例菌株复活失败、2例菌株丢失,剩下42例菌株完成测序,其余有5株菌株RRDR区未发生突变,剩余的37株在rpoB基因的RRDR区有不同位点及不同类型的变异,其中有2株在508和509位点发生缺失突变,其它突变的位点有511、516、526、531、533。多数突变位点集中在526位,突变类型包括His526Asn、His526Leu、His526Gly、His526Cys四种,其余位点突变形式为Leu511Pro、Asp516Tyr、Leu533Pro。在511、516、526、533位点突变中,MIC测定除了一株突变类型为His526Leu的菌株为32 μg/ml外,其余位点突变均表现为低水平耐药或敏感,而531位点突变中Ser531Trp、Ser531Leu均表现为高水平耐药。 结论 基于rpoB测序和MIC测定的结果显示特定rpoB基因突变可能导致结核分枝杆菌利福平耐药水平的改变,结核分枝杆菌利福平耐药(Xpert MTB/RIF)检测与(Bactec MGIT 960)检测结果不一致。

Discordance across molecular and phenotypic methodsfor drug susceptibility testing of rifampicin-resistant Mycobacterium tuberculosis

Objective To analyze the mechanism of discordance between molecular drug susceptibility testing (Xpert MTB/RIF assay) and phenotypic drug susceptibility testing (Bactec MGIT 960 culture system) of rifampicin-resistant Mycobacterium tuberculosis. Methods We collected 46 specimens (including 39 specimens that were rifampicin-resistant by the Xpert MTB/RIF assay but rifampicin-sensitive by MGIT 960 culture and 7 specimens that were rifampicin-sensitive by the Xpert MTB/RIF assay but rifampicin-resistant by MGIT 960 culture) from 8,274 patients with Xpert MTB/RIF detection in the First Affiliated Hospital of Changsha Medical University from October 2015 to April 2018, then tried to get the isolates form the 46 specimens and figured out the rifampicin resistance determining region (RRDR) with rpoB gene detection. The minimum inhibitory concentration (MIC) in the recovered isolates was simultaneously determined, and the degree of resistance for different mutation isolates was observed. Results Among the 46 specimens, 2 isolates were failed and another 2 were lost. The remaining 42 isolates were sequenced, and there were 5 isolates without rpoB mutation and 37 isolates had diverse gene variations. The main mutation loci were concentrated in 511, 516, 526, 531 and 533 sites. The leading locus was 526, and there were 4 types of mutation, including His526Asn, His526Leu, His526Gly and His526Cys. The types of mutation in other loci were Leu511Pro, Asp516Tyr and Leu533Pro. As for the isolates with mutation located in 511, 516, 526 and 533 sites, the MIC of one isolate with His526Leu mutation was 32 μg/ml, but the others displayed low-level susceptibility or resistance. As for the isolates with mutation located in 531, Ser531Trp and Ser531Leu mutation displayed high-level resistance. Conclusions The Results based on rpoB sequence and MIC measurement show that the specific rpoB gene mutation may lead to the changes of rifampin resistance in Mycobacterium tuberculosis. There are discordant Results between the Xpert MTB/RIF assay and Bactec MGIT 960 culture system for detection of rifampin-resistant Mycobacterium tuberculosis.