利福布汀抗结核分枝杆菌活性及其耐药性与rpoB基因突变关系的探讨

Analysis of the antimycobacterial activities of rifabutin and the relationship between drug-resistance and rpoB mutations of Mycobacterium tuberculosis

目的比较利福平和利福布汀的体外抗MTB活性，分析其交叉耐药性，评价利福平和利福布汀耐药性与rpoB突变的关系。方法采用微量平板Alamar Blue检测（MABA）法，检测利福平和利福布汀对MTB临床分离菌株168株的抗菌活性，并对其rpoB基因核心区进行DNA序列测定。两组间基因突变率的比较采用Х^2检验。结果66株利福平敏感菌株均对利福布汀敏感（MIC≤0．125mg／L），未检测到rpoB基因耐药决定区存在突变；102株利福平耐药菌株中有76株同时对利福布汀耐药（MIC〉0．5mg／L），交叉耐药率为74．5％（76／102）；26株MIC≤4mg／L的利福平耐药菌株仍对利福布汀敏感（MIC≤0．5mg／L）；516、526和531位点的氨基酸改变与利福平和利福布汀耐药均有关，而511和533位点的氨基酸改变可能仅与利福平耐药有关，利福布汀耐药菌株的rpoB基因突变率（92．1％，70／76）显著高于利福布汀敏感菌株（23．9％，22／92），差异有统计学意义（Х^2=78．12，P〈0．05）。结论对利福平低度耐药（MIC≤4mg／L）的MTB仍对利福布汀敏感。MTB的rpoB基因突变可用于利福平耐药性检测，且对检测利福布汀的耐药性也有参考意义。

Objective To compare the antimycobaeterial activities of rifampicin （RFP） and rifabutin （RBT）, and to evaluate the correlation between RBT resistance and genetic alterations in the rpoB gene. Methods The microplate-based alamar blue assay （MABA） method was performed to detect the antimycobacterial activities of RFP and RBT in 168 strains of Mycobacteriurn tuberculosis （M. tuberculosis）. Meanwhile, we also analyzed the 81 bp core region of rpoB gene by DNA sequencing. The rate of gene mutations was analyzed by chi-square test. Results RBT was sensitive for all of the 66 RFP-sensitive strains with no mutations in 81 bp core region of rpoB gene. But of the 102 RFP-resistant strains, 76 strains were also resistant to RBT. Cross resistance between RFP and RBT was 74. 5% （76/102）. Alterations at codons 516, 526, 531 in the rpoB gene correlated with resistance to both RFP and RBT. While point mutations at codons 511 and 533 possibly influenced the susceptibility to RFP but not to RBT. The mutation rate （92. 1% , 70/76） of rpoB gene of RBT-resistant strains was significantly higher than that （23.9% , 22/ 92） of RBT-sensitive strains （ Х^2 = 78. 12, P 〈 0.05 ） . Conclusions RBT was more active against M. tuberculosis as compared to RFP. The RFP-resistant strains with MIC ≤4 mg/L were still susceptible to RBT. Our results suggest that analysis of genetic alterations in the rpoB gene is useful for predicting RFP- resistance, and may have implications for evaluating RBT-resistance.