Rinder H, Mieskes K T, Löscher T
Department of Infectious Diseases and Tropical Medicine, University of Munich, Germany.
Int J Tuberc Lung Dis. 2001 Apr;5(4):339-45.
Drug resistance in Mycobacterium tuberculosis is often linked to specific mutations in a limited number of resistance genes. Detection of these mutations in a cultured isolate can predict the resistant phenotype. Genotypic analysis of the mycobacteria directly in a clinical specimen would result in considerable time saving for resistance prediction.
To find out whether resistance-predicting genotypes of mycobacteria found after cultivation always give a good reflection of those in the original clinical sample.
Restriction fragment length polymorphisms of repetitive polymerase chain reaction (PCR) amplification and cloning of PCR products were used as nonintegrative methods to describe the composition of katG, rpsL and embB genotypes involved in resistance to isoniazid, streptomycin and ethambutol, respectively, in the original sample. This result was then compared to the phenotypic resistance profile after cultivation.
Using both methods, mixed, heteroresistant populations could be detected in almost every fifth analyzed sample (katG: 5 of 16; rpsL: 3 of 17; embB: 1 of 21). Direct sequencing, a widely used integrative method, repeatedly failed to detect heteroresistance.
Heteroresistance is a valid phenomenon in clinical tuberculosis. It is not rare and not restricted to a particular resistance gene, and is obscured by cultivation as well as by some, not all, culture-independent resistance prediction tests.
结核分枝杆菌的耐药性通常与少数耐药基因中的特定突变有关。在培养的分离株中检测这些突变可以预测耐药表型。直接对临床标本中的分枝杆菌进行基因分型分析将大大节省耐药性预测的时间。
了解培养后发现的分枝杆菌耐药性预测基因型是否总能很好地反映原始临床样本中的基因型。
采用重复聚合酶链反应（PCR）扩增的限制性片段长度多态性分析以及PCR产物克隆作为非整合方法，分别描述原始样本中与对异烟肼、链霉素和乙胺丁醇耐药相关的katG、rpsL和embB基因型的组成。然后将该结果与培养后的表型耐药谱进行比较。
使用这两种方法，在几乎每五个分析样本中都能检测到混合的、异质性耐药群体（katG：16个样本中的5个；rpsL：17个样本中的3个；embB：21个样本中的1个）。直接测序是一种广泛使用的整合方法，多次未能检测到异质性耐药。
异质性耐药在临床结核病中是一种真实存在的现象。它并不罕见，也不限于特定的耐药基因，并且会被培养以及一些（并非全部）非培养依赖性耐药预测试验所掩盖。
