Tahmasebi P, Farnia P, Sheikholslami Fm, Velayati Aa
Mycobacteriology Research Centre, National Research Institute of Tuberculosis and Lung Disease (NRITLD), WHO & UNION Collaborating Centre for TB & Lung Diseases, Darabad, Tehran, Iran.
Iran J Microbiol. 2012 Dec;4(4):165-70.
Resistance in Mycobacterium tuberculosis is caused by mutations in genes encoding drug targets. Investigators have already demonstrated the existence of mutations in codons 88 to 94 in the gyrA gene and also in codons 1400, 1401, and 1483 of rrs gene among extensively and extremely drug resistant tuberculosis (XDR & XXDR-TB) strains. The aim of this study was to identify the XDR and XXDR-TB stains based on their mutational analysis.
Susceptibility testing against first and second-line anti-tuberculosis drugs was performed by the proportional method. Based on susceptibility results, samples were later analyzed, using PCR-SSCP and PCR-RFLP for detection of mutation in gyrA and rrs genes.
Overall, using proportional method, sixty-three strains (64.9%) were identified as MDR, 8(8.2%) as non-MDR and 26 strains (26.8%) were susceptible. Thirty-one cases (31.9%) were amikacin-resistant and 18 (18.5%) samples were ciprofloxacin-resistant. Using PCR-SSCP and PCR-RFLP, we identified 6(6.2%) and 7(7.2%) resistant strains, respectively. Discrepancy in strains was cross-checked by sequencing. The results showed no mutation in 66.6% and 77.4% of CIP and AMK- resistant strains.
Rapid detection of drug-resistant Mycobacterium tuberculosis using molecular techniques could be effective in determining therapeutic regimen and preventing the spread of XDR and MDR TB in the community. We should still keep in mind that a high number of resistant strains may have no mutation in proposed candidate genes.
结核分枝杆菌的耐药性是由编码药物靶点的基因突变引起的。研究人员已经证明，在广泛耐药和极度耐药结核病（XDR & XXDR-TB）菌株中，gyrA基因的88至94密码子以及rrs基因的1400、1401和1483密码子存在突变。本研究的目的是通过突变分析鉴定XDR和XXDR-TB菌株。
采用比例法对一线和二线抗结核药物进行药敏试验。根据药敏结果，随后使用PCR-SSCP和PCR-RFLP对样本进行分析，以检测gyrA和rrs基因中的突变。
总体而言，采用比例法，63株（64.9%）被鉴定为耐多药，8株（8.2%）为非耐多药，26株（26.8%）敏感。31例（31.9%）对阿米卡星耐药，18例（18.5%）样本对环丙沙星耐药。使用PCR-SSCP和PCR-RFLP，我们分别鉴定出6株（6.2%）和7株（7.2%）耐药菌株。通过测序对菌株差异进行交叉核对。结果显示，66.6%的环丙沙星耐药菌株和77.4%的阿米卡星耐药菌株未发生突变。
使用分子技术快速检测耐药结核分枝杆菌可有效确定治疗方案并防止XDR和MDR TB在社区传播。我们仍应牢记，大量耐药菌株在提议的候选基因中可能没有突变。
