DNA芯片快速检测结核分枝杆菌利福平耐药rpoB基因突变

目的建立快速检测结核分枝杆菌利福平（RFP）耐药rpoB基因突变的DNA芯片。方法从34株临床痰样本中提取结核分枝杆菌的基因组DNA，采用聚合酶链反应（PCR）扩增含有rpoB基因突变位点的特异DNA片段，荧光标记后与芯片上含有特异突变位点的寡核苷酸探针进行杂交，同时与DNA测序法比较。结果用DNA芯片检测出19株耐药株和15株敏感株，且结果与DNA测序相同，准确率可达88．2％，敏感性为78．9％，特异性为100．0％。结论DNA芯片快速检测结核分枝杆菌对RFP的耐药rpoB基因突变是一种操作简便、准确性、敏感性和特异性较高，且易于开展的方法。     

实时荧光PCR分子信标检测耐利福平结核分枝杆菌印rpoB基因

目的 应用实时荧光PCR分子信标技术,建立快速检测临床标本中结核分枝杆菌利福平rpoB相关耐药突变点方法,探讨其缩短耐药实验报告时间的临床应用价值.方法 以分枝杆菌药物敏感性实验绝对浓度法为标准,12株非结核分枝杆菌、4株非分枝杆菌作对照,对174例结核患者临床分离株应用实时荧光PCR分子信标方法,检测利福平rpoB核心区域的耐药突变点并将结果与直接测序进行比较.结果 (1)实时荧光PCR分子信标方法:82例结核分枝杆菌利福平敏感菌株中,3例发生rpoB基因突变,特异度为96.3%;92例结核分枝杆菌利福平耐药菌株中,82例检出耐药突变,敏感度为89.1%;准确性为92.5%.(2)DNA直接测序分析:82例结核分枝杆菌利福平敏感株中,1例发生rpoB基因突变,特异度为98.8%;92例结核分枝杆菌利福平耐药菌株中,83例发生:rpoB基因突变,敏感度为90.2%;准确性为94.2%.检测174株结核分枝杆菌临床分离菌株,与实时荧光PCR分子信标方法检测一致性为98.3%(171/174).结论 实时荧光PCR分子信标方法检测耐利福平结核分枝杆菌rpoB基因突变点可作为结核患者快速耐药检测的初筛方法之一.     

结核分枝杆菌对利福平和异烟肼耐药基因突变快速检测方法的建立

目的建立结核分枝杆菌对利福平和异烟肼耐药基因突变的快速检测方法。方法根据结核分枝杆菌标准株H37Rv序列，自行设计覆盖rpoB、katG、inhA基因突变区的系列寡核苷酸探针，并检测临床样品中结核分枝杆菌的基因突变情况，以此来判断耐药结果。结果在56个利福平耐药菌株中，有50个菌株都在rpoB基因上榆出有突变，利福平耐药突变检出率为89．3％（50／56）；有30个利福平敏感菌株rpoB基因上都未检出突变。有58个异烟肼培养的耐药菌株中有47个在katG或inhA基因上检出有突变，异烟肼耐药突变检出率为81．0％（47／58）；有30个异烟肼敏感菌株katG或inhA基因上未检出突变。结论用膜芯片检测结核分枝杆菌对利福平和异烟肼的耐药性，具有较高的特异性和敏感性，可用于临床结核分枝杆菌耐药性的检测。     

耐药结核分枝杆菌链霉素耐药基因的分子流行病学研究及其快速检测

目的探讨结核分枝杆菌对链霉素的耐药分子机制，建立基于焦磷酸测序（pyrosequencing）技术的快速检测结核分枝杆菌链霉素耐药性的方法。方法用扩增后直接测序的方法检测了150株结核分枝杆菌链霉素耐药株的rpsL基因，并用pyrosequencing技术对其中20株的rpsL基因43位密码子进行了检测。结果150株链霉素耐药株中2株rpsL基因缺失，115株rpsL基因存在突变，突变率为77．7％，最主要的突变形式是43位密码子突变，pyrosequencing的检测结果与测序结果相符。结论rpsL基因突变是产生链霉素耐药的重要分子机制，pyrosequencing技术具有快速、准确等特点，适用于对耐链霉素结核分枝杆菌进行快速高通量的检测。     

焦磷酸测序技术检测耐多药结核分枝杆菌

目的利用焦磷酸测序技术,建立结核分枝杆菌菌株耐多药检测方法,并与Bactec MGIT 960药敏法进行比较。方法设计rpoB、katG基因PCR扩增引物和焦磷酸测序引物,建立结核分枝杆菌菌株焦磷酸测序检测方法。利用新确立的焦磷酸测序法检测202株临床分离的耐多药结核分枝杆菌的利福平、异烟肼耐药性。结果与BACTEC MGIT 960法检测药物耐药性结果比较,焦磷酸测序检测多耐药结核分枝杆菌临床分离株的敏感性与特异性为72.8%[95%可信区间(confidence in-terval,CI):66.3%~78.4%]及90.0%(95%CI:80.1%~95.1%)。结论新确立的焦磷酸测序技术可快速检测结核分枝杆菌对利福平、异烟肼的耐药性,其可作为耐多药结核分枝杆菌药敏有效的检测工具。     

PCR-SSCP快速检测结核分枝杆菌耐利福平rpoB基因的研究

目的探讨PCR—SSCP技术检测结核分枝杆菌耐利福平rpoB基因作为新的分子药敏试验方法的价值。方法应用PCR—SSCP技术检测结核分枝杆菌耐利福平rpoB基因核心区的突变，同时对片段长度为215bp的PCR扩增产物进行测序分析。受试菌为23株利福平敏感结核分枝杆菌以72．35株利福平抗性结核分枝杆菌。结果23株利福平敏感结核分枝杆菌分别用PCR—SSCP和PCR扩增片段测序均没有检测到巾0B碱基突变。而在35株利福平抗性菌株中，PCR—SSCP检测到31株与H37Rv标准株不同的带谱，PCR—SSCP检测基因突变的敏感度和特异度分别为88．6％（31／35）和100％（23／23）。对35株利福平抗性菌株PCR扩增产物进行测序分析，在其中32株中检出了基因突变。测序分析检测基因突变的敏感度和特异度分别为91．4％（32／35）和100％（23／23）。卡方检验，PCR—SSCP和PCR扩增片段测序两种方法的敏感度之间没有显著性差异（P〉0．05）。若以DNA测序为标准，则PCR—SSCP检测基因突变的准确度、敏感度和特异度分别为93．1％（54／58），96．9％（31／32）和100％（23／23）。结论PCR—SSCP检测结核分枝杆菌耐利福平rpoB基因突变可用于利福平药物敏感度的快速测定。     

PCR—SSCP快速检测结核分枝杆菌耐利福平rpoB基因的研究

目的探讨PCR—SSCP技术检测结核分枝杆菌耐利福平rpoB基因作为新的分子药敏试验方法的价值。方法应用PCR—SSCP技术检测结核分枝杆菌耐利福平rpoB基因核心区的突变，同时对片段长度为215bp的PCR扩增产物进行测序分析。受试菌为23株利福平敏感结核分枝杆菌以72．35株利福平抗性结核分枝杆菌。结果23株利福平敏感结核分枝杆菌分别用PCR—SSCP和PCR扩增片段测序均没有检测到巾0B碱基突变。而在35株利福平抗性菌株中，PCR—SSCP检测到31株与H37Rv标准株不同的带谱，PCR—SSCP检测基因突变的敏感度和特异度分别为88．6％（31／35）和100％（23／23）。对35株利福平抗性菌株PCR扩增产物进行测序分析，在其中32株中检出了基因突变。测序分析检测基因突变的敏感度和特异度分别为91．4％（32／35）和100％（23／23）。卡方检验，PCR—SSCP和PCR扩增片段测序两种方法的敏感度之间没有显著性差异（P〉0．05）。若以DNA测序为标准，则PCR—SSCP检测基因突变的准确度、敏感度和特异度分别为93．1％（54／58），96．9％（31／32）和100％（23／23）。结论PCR—SSCP检测结核分枝杆菌耐利福平rpoB基因突变可用于利福平药物敏感度的快速测定。     

耐利福平结核分枝杆菌 rpoA、rpoB、rpoC和rpoZ突变的研究

目的：了解结核分枝杆菌rpoA、rpoB、rpoC和rpoZ突变特征及其与利福平耐药的关系。方法对140株临床分离结核分枝杆菌进行利福平敏感性试验,并对耐利福平株分别进行rpoB耐药决定区及rpoA、rpoB、rpoC及rpoZ全基因测序。结果140株结核分枝杆菌中57株对利福平耐药。57株耐利福平结核分枝杆菌中,52株（91.2%）存在突变,其中50株为rpoB基因突变,2株为rpoC突变。在rpoB 765、1001、1156位及rpoC 51位发现新的突变位点。结论结核分枝杆菌对利福平耐药主要与rpoB和rpoC基因突变有关。     

检测结核分枝杆菌rpoB基因突变的研究

目的：建立聚合酶链反应－单链构象多态性（PCR－SSCP）检测结核分枝杆菌rpoB基因突变的方法，并评价共临床应用的价值。方法：依据结核分枝杆菌rpoB基因的耐利福平决定区设计引物，用PCR从临床分离株和直接从痰标本中扩增rpoB基因片段；对扩得的rpoB基因片段做DNA SSCP分析，并随机测定rpoB片段的序列。结果：PCR从所有212株结核分枝杆菌中均扩得230bp片段135份抗酸染色阳性的痰标本中，有113份扩得阳性片段（83．7％），在SSCP分析中，140份经L－J药敏试验检测为利福平耐受的结核分枝杆菌，有130份有rpoB基因突变（符合率为92．9％），72份经L－J药敏试验检测为利福平敏感的菌，有67份的rpoB基因无突变（符合率为93．1％），测序分析发现57份经SSCP检测为突变的rpoB片段均有序列改变，10份经SSCP分析为无突变的有8份无序列改变，SSCP与测序结果的符合率为94．0％，在本研究的菌株中，耐多药结核病（MDR－TB）占76．4％（107／140），有92．5％（99／107）耐多药菌株经SSCP检测有rpoB突变。结论：建立的PCR－SSCP分析方法，是一种较准确和稳定的检测结核分枝杆菌rpoB基因突变的方法，可用于临床快速分析患者结核分枝杆菌对利福平的耐药性，并可作为MDR－TB判断的一个重要指标。     

耐药结核分枝杆菌基因突变分析

目的 探讨结核分枝杆菌耐药表型与基因突变位点之间的相互关系.方法 采用序列特异性引物分别扩增92株结核分枝杆菌利福平耐药基因rpoB,异烟肼耐药基因katG、inhA、ahpC,链霉素耐药基因rrs、rpsL,乙胺丁醇耐药基因embB及喹诺酮耐药基因gyrA,SSCP筛选出突变序列,DNA测序分析突变性质.结果 59株利福平耐药株rpoB基因突变检出率94.9%(56/59),以Ser450Trp突变最多;90株异烟肼耐药株中,katG基因突变检出率38.9%(35/90),以Ser315Thr最多,3株检出inhA基因突变,ahpC基因无突变检出;34株喹诺酮耐药株中gyrA基因突变检出率82.4%(28/34),主要为Asp94Gly,其次为Ala90Val;31株链霉素耐药株中,15株检出rrs突变,最常见为A514C和A1041G,10株发生rpsL Lys88Arg突变,总的链霉素基因突变检出率为77.4%(24/31);31株乙胺丁醇耐药株中embB 基因突变检出率19.4%(6/31),主要为Met306Val.结论 耐药结核分枝杆菌耐药情况较为严重,以DNA测序为基础的基因突变分析能快速有效地检测结核分枝杆菌的rpoB、katG、gyrA、rrs、rpsL、embB 等耐药分子标识,显示了西安地区耐药性结核分枝杆菌的突变特点,为结核病的临床诊断和合理用药提供了实验依据.     

武汉地区耐利福平结核分枝杆菌rpoB基因突变分析

摘要：目的：探讨武汉地区结核分枝杆菌（MTB）利福平耐药株rpoB基因的突变特征。 方法：对76例MTB临床分离株包括rpoB核心区域81 bp碱基在内的428 bp碱基进行PCR测定,并进行DNA序列分析。 结果：76例临床分离MTB中利福平耐药株56例,敏感株20例。耐药株中92.9%（52/56）存在突变,共涉及10个密码子的18种突变类型。 531、526为常见突变位点,其突变率分别为57.7%(30/52)、19.2%(10/52);联合突变率为13.5%（7/52）;同时发现了509位（AGC→AGA）新的突变类型和国内少见的517位CAG缺失类型。 结论：rpoB基因突变在武汉地区利福平耐药MTB中广泛存在,并存在新的突变位点。     

Characterization of rifampin-resistance in pathogenic mycobacteria.

The emergence of rifampin-resistant strains of pathogenic mycobacteria has threatened the usefulness of this drug in treating mycobacterial diseases. Critical to the treatment of individuals infected with resistant strains is the rapid identification of these strains directly from clinical specimens. It has been shown that resistance to rifampin in Mycobacterium tuberculosis and Mycobacterium leprae apparently involves mutations in the rpoB gene encoding the beta-subunit of the RNA polymerases of these species. DNA sequences were obtained from a 305-bp fragment of the rpoB gene from 110 rifampin-resistant and 10 rifampin-susceptible strains of M. tuberculosis from diverse geographical regions throughout the world. In 102 of 110 rifampin-resistant strains 16 mutations affecting 13 amino acids were observed. No mutations were observed in rifampin-susceptible strains. No association was found between particular mutations in the rpoB gene and drug susceptibility patterns of multidrug-resistant M. tuberculosis strains. Drug-resistant M. tuberculosis strains from the same outbreak and exhibiting the same IS6110 DNA fingerprint and drug susceptibility pattern contained the same mutation in the rpoB gene. However, mutations are not correlated with IS6110 profiling outside of epidemics. The evolution of rifampin resistance as a consequence of mutations in the rpoB gene was documented in a patient who developed rifampin resistance during the course of treatment. Rifampin-resistant strains of M. leprae, Mycobacterium avium, and Mycobacterium africanum contained mutations in the rpoB gene similar to that documented for M. tuberculosis. This information served as the basis for developing a rapid DNA diagnostic assay (PCR-heteroduplex formation) for the detection of rifampin susceptibility of M. tuberculosis.     

Mutation analysis of mycobacterial rpoB genes and rifampin resistance using recombinant Mycobacterium smegmatis

Rifampin is a major drug used to treat leprosy and tuberculosis. The rifampin resistance of Mycobacterium leprae and Mycobacterium tuberculosis results from a mutation in the rpoB gene, encoding the β subunit of RNA polymerase. A method for the molecular determination of rifampin resistance in these two mycobacteria would be clinically valuable, but the relationship between the mutations and susceptibility to rifampin must be clarified before its use. Analyses of mutations responsible for rifampin resistance using clinical isolates present some limitations. Each clinical isolate has its own genetic variations in some loci other than rpoB, which might affect rifampin susceptibility. For this study, we constructed recombinant strains of Mycobacterium smegmatis carrying the M. leprae or M. tuberculosis rpoB gene with or without mutation and disrupted their own rpoB genes on the chromosome. The rifampin and rifabutin susceptibilities of the recombinant bacteria were measured to examine the influence of the mutations. The results confirmed that several mutations detected in clinical isolates of these two pathogenic mycobacteria can confer rifampin resistance, but they also suggested that some mutations detected in M. leprae isolates or rifampin-resistant M. tuberculosis isolates are not involved in rifampin resistance.     

银染单链构象多态性技术检测结核杆菌rpoB基因突变

目的探讨分子生物学方法在临床标本结核分枝杆菌利福平（ＲＦＰ）耐药性评估中的应用价值。方法设计针对ｒｐｏＢ基因１８３ｂｐ扩增引物,运用聚合酶链反应单链构象多态性分析（ＰＣＲＳＳＣＰ）银染色方法,检测了４５株结核杆菌临床分离株,并对其中部分菌株进一步做了ＤＮＡ序列分析。结果以药敏试验结果为对照,有１６株ＲＦＰ敏感株及２６株ＲＦＰ耐药株经ＳＣＰ方法得到检测,阳性占９３．３％,特异性１００％。对部分菌株１８３ｂｐ片断测序结果显示,ＲＦＰ敏感株无ｒｐｏＢ基因突变,耐药株均发生碱基突变,分别导致编码５３１及５２６位点的氨基酸改变。结论银染ＰＣＲＳＣＰ方法具有简便,快速,准确的特点,提高敏感性,可以对临床标本结核杆菌利福平耐药突变进行鉴定。序列分析证明结核分枝杆菌利福平耐药菌株有ｒｐｏＢ基因突变。     

耐利福平结核分枝杆菌rpoB基因序列研究

目的 研究杭州地区结核分枝杆菌（Mycobacterium tuberculosis）对利福平（RFP）的耐受与rpoB基因突变的关系。方法 随机挑选了90例结核杆菌感染的病例。选择了利福平作为主要的药物进行药敏实验，PCR扩增39株耐RFP结核分支杆菌的rpoB基因片段（580bp）；测定扩增片段的序列。并与美国国立生物信息中心（www．ncbi．nlm．nih．gov／nucleotide）检索获得结核杆菌野生株（利福平敏感株）序列（登陆号：AJ749948）作对比分析。结果 结果显示PCR结核测序方法得到了39例结核杆菌耐药株。51例敏感株，与药敏实验的方法检测的结果完全一致。测定的11株临床分离的耐药株中，526位或531位有突变，其中526位有突变的有7株，占耐药测定株63．6%，531位突变的有4株。占耐药测定株36．4％。未见两位点同时突变。检测的11株敏感株，未见526位或531位有突变。结论 杭州地区结核分支杆菌耐利福平的发生与rpoB基因的526位或531位突变密切相关，与国外的报告基本相似。但526位突变占耐药测定株高达63．6％。如此高比例目前国内外未见相似报道。PCR扩增和产物测序将是临床检测结核分支杆菌耐利福平和耐多药的一种迅速、准确的方法。     

焦磷酸测序技术检测结核分枝杆菌四种药物耐药性

目的 利用焦磷酸测序技术检测结核分枝杆菌对利福平、异烟肼、氧氟沙星、阿米卡星的耐药性,并对其临床应用进行评价.方法 收集上海市肺科医院2008-2009年临床确诊的肺结核患者的痰标本培养阳性结核分枝杆菌89株.所有菌株按<结核病诊断实验室检验规程>进行分枝杆菌培养、菌种鉴定.另外10株已知药敏结果的结核分枝杆菌来自上海市肺科医院菌株库.利用焦磷酸测序技术,以10株已知药敏结果和经直接测序已知耐药基因突变情况的结核分枝杆菌为试验菌株,探索焦磷酸测序检测结核分枝杆菌rpoB、katG、gyrA、rrs耐药基因的最佳模式,并用该条件检测89株结核分枝杆菌临床分离株,检测结果与Bactec 960药敏法进行比较.结果 rpoB、gyrA基因检测宜采用焦磷酸测序序列分析模式,katG、rrs基因检测宜采用焦磷酸测序单核苷酸多态性模式.以Bactec 960药敏法测定结果为判断标准,则焦磷酸测序法检测89株结核分枝杆菌临床分离株对利福平、异烟肼、氧氟沙星、阿米卡星耐药性的敏感度分别为98.0%、64.1%、79.5%、78.3%,特异度分别为97.5%、100.0%、90.0%、100.0%,准确性分别为97.8%、77.5%、85.4%、94.4%,该法检测利福平、氧氟沙星、阿米卡星的检测结果与Bactec 960药敏检测结果一致性较好,Kappa值均≥0.7.结论 焦磷酸测序技术检测结核分枝杆菌对利福平、异烟肼、氧氟沙星、阿米卡星耐药性具有快速、准确、高通量的优点,是一种可对结核分枝杆菌多种药物耐药性进行快速检测的方法.

Abstract：

Objective To develop an assay to determine Mycobacterium tuberculosis resistance to rifampin, isoniazid, ofloxacin and amikacin by pyrosequencing and evaluate the value of this method in clinical application. Methods Eighty-nine clinical isolates of Mycobacterium tuberculosis from tuberculosis patients were collected from Shanghai Pulmonary Hospital during 2008 to 2009. All strains were isolated from decontaminated sputum, cultured on Lowenstein-Jensen media and identified by traditional biochemical tests with standard methods. Ten Mycobacterium tuberculosis were selected from the strain bank of Shanghai Pulmonary Hospital. The optimal conditions of detection of rpoB, katG, gyrA and rrs gene by pyroseuencing were determined, using the 10 Mycobacterium tuberculosis strains whose drug susceptibility of Bactec 960 and sequence of rpoB, katG, gyrA, rrs gene were known. Then the drug susceptibility of 89 Mycobacterium tuberculosis clinical isolate strains were detected by pyrosequencing using this conditions and the results were compared with that of the Bactec 960 methods. Results The pyrosequencing program of sequence analysis was suitable for the detection of the mutations of rpoB and gyrA genes, and the program of single nucleotide polymorphism was suitable for katG and rrs genes. Among the 89 Mycobacterium tuberculosis clinical isolates,when using the drug susceptibility of Bactec 960 as the standard, the sensitivity of rifampin, isoniazid,ofloxacin and amikacin is 98.0%, 64. 1%, 79.5%, 78. 3% respectively, the specificity is 97.5%,100. 0%, 90. 0%, 100. 0% respectively, the accuracy is 97.8%, 77. 5%, 85.4%, 94. 4% respectively,tested by pyrosequencing. The results of the detection of resistance to rifampin, isoniazid, ofloxacin and amikacin in Mycobacterium tuberculosis using pyrosequencing technique were almost the same with that of Bactec 960, and Kappa ≥0. 7 in each detection. Conclusion Pyrosequencing is thus a rapid, accurate and high throughput method for detecting Mycobacterium tuberculosis resistance to these four drugs.     

线性探针分析法检测结核分枝杆菌rpoB耐药基因突变的研究

目的研制线性探针分析法检测结核分枝杆菌(结核菌)rpoB基因耐药突变试剂盒。方法设计15条结核菌rpoB基因野生型和突变型的线性探针，固定尼龙膜上；在rpoB基因引物上标记生物素，扩增结核菌DNA，获得生物素标记扩增产物，与rpoB基因线性探针杂交，加入标记过氧化物酶的亲合素，再加四甲基联苯胺显色。结果应用线性探针分析法检测87株结核菌，其与rpoB基因直接测序法、传统药敏法符合率分别为98．8％(82／83)和94．3％(82／87)。结论线性探针分析法检测rpoB耐药基因突变是一种操作简便、特异性高、敏感性高，易开展的方法。     

Molecular basis of rifampin and isoniazid resistance in Mycobacterium bovis strains isolated in Sardinia, Italy

Fourteen of 22 (68%) Mycobacterium bovis strains isolated from cattle in Sardinia were found to be resistant to rifampin and isoniazid. Analysis of the rpoB and the katG, oxyR-ahpC, and inhA gene regions of these strains was performed in order to investigate the molecular basis of rifampin and isoniazid resistance, respectively. The most frequent mutation, encountered in 6 of 10 strains (60%), was in the rpoB gene; it occurred, at codon position 521 and resulted in leucine changed to proline. This suggests that codon 521 may be important for the development of rifampin resistance in M. bovis. Resistance to isoniazid is associated in Mycobacterium tuberculosis with a variety of mutations affecting one or more genes. Our results confirm the difficulty of interpreting the sequence variations observed in clinical strains of M. bovis. M. bovis strains isolated from the same geographic area showed similar mutations within the genes responsible for rifampin and isoniazid resistance. Our results represent the first study to elucidate the molecular genetic basis of drug resistance in M. bovis isolated from cattle.     

The rpoB gene of Mycobacterium tuberculosis.

A portion of the Mycobacterium tuberculosis gene encoding the beta subunit of RNA polymerase (rpoB) was amplified by PCR using degenerate oligonucleotides and used as a hybridization probe to isolate plasmid clones carrying the entire rpoB gene of M. tuberculosis H37Rv, a virulent, rifampin-susceptible strain. Sequence analysis of a 5,084-bp SacI genomic DNA fragment revealed a 3,534-bp open reading frame encoding an 1,178-amino-acid protein with 57% identity with the Escherichia coli beta subunit. This SacI fragment also carried a portion of the rpoC gene located 43 bp downstream from the 3' end of the rpoB open reading frame; this organization is similar to that of the rpoBC operon of E. coli. The M. tuberculosis rpoB gene was cloned into the shuttle plasmid pMV261 and electroporated into the LR223 strain of Mycobacterium smegmatis, which is highly resistant to rifampin (MIC > 200 micrograms/ml). The resulting transformants were relatively rifampin susceptible (MIC = 50 micrograms/ml). Using PCR mutagenesis techniques, we introduced a specific rpoB point mutation (associated with clinical strains of rifampin-resistant M. tuberculosis) into the cloned M. tuberculosis rpoB gene and expressed this altered gene in the LR222 strain of M. smegmatis, which is susceptible to rifampin (MIC = 25 micrograms/ml). The resulting transformants were rifampin resistant (MIC = 200 micrograms/ml). The mutagenesis and expression strategy of the cloned M. tuberculosis rpoB gene that we have employed in this study will allow us to determine the rpoB mutations that are responsible for rifampin resistance in M. tuberculosis.