Rouse D A, Morris S L
Laboratory of Mycobacteria, Food and Drug Administration, Bethesda, Maryland 20892.
Infect Immun. 1995 Apr;63(4):1427-33. doi: 10.1128/iai.63.4.1427-1433.1995.
Genetic and biochemical studies have suggested a link between reduced catalase activity and resistance to isoniazid in Mycobacterium tuberculosis. In this study, we examined the molecular mechanisms of resistance to isoniazid with six in vitro mutants of the M. tuberculosis complex (Mycobacterium bovis and M. tuberculosis). Five of six mutants resistant to isoniazid were negative by catalase assays. Immunoblot analyses using a polyclonal antibody against the katG gene product (catalase-peroxidase) demonstrated that the enzyme is not produced in four of these isoniazid-resistant strains. A complete deletion of the katG gene was detected in only one of these isoniazid-resistant M. tuberculosis complex strains by Southern blot analyses. In two other resistant strains, partial deletions of the katG gene were identified. A point mutation which resulted in the insertion of a termination codon in the katG coding sequence caused a catalase-negative phenotype in a fourth strain. Of the two resistant strains which produce the enzyme, one was shown to be negative by a catalase assay. Single-stranded conformational polymorphism and DNA sequence analyses identified a mutation in the katG gene of this strain which may contribute to reduced enzymatic activity and subsequent isoniazid resistance. These data demonstrate that genetic alterations to the katG gene other than complete deletions are prevalent and may contribute significantly to the number of cases of isoniazid-resistant tuberculosis.
遗传学和生物化学研究表明，结核分枝杆菌中过氧化氢酶活性降低与对异烟肼的耐药性之间存在联系。在本研究中，我们用结核分枝杆菌复合群（牛分枝杆菌和结核分枝杆菌）的六个体外突变株研究了对异烟肼耐药的分子机制。六个异烟肼耐药突变株中有五个过氧化氢酶检测呈阴性。使用针对katG基因产物（过氧化氢酶-过氧化物酶）的多克隆抗体进行的免疫印迹分析表明，在这些异烟肼耐药菌株中有四个未产生该酶。通过Southern印迹分析，在这些异烟肼耐药的结核分枝杆菌复合群菌株中仅检测到一株katG基因完全缺失。在另外两株耐药菌株中，鉴定出katG基因部分缺失。在第四株菌株中，一个导致katG编码序列中插入终止密码子的点突变导致了过氧化氢酶阴性表型。在两株产生该酶的耐药菌株中，一株过氧化氢酶检测呈阴性。单链构象多态性和DNA序列分析确定该菌株的katG基因存在突变，这可能导致酶活性降低并随后产生异烟肼耐药性。这些数据表明，除了完全缺失外，katG基因的遗传改变很普遍，可能在很大程度上导致了异烟肼耐药结核病的病例数。
