DST/NRF Centre of Excellence for Biomedical Tuberculosis Research/MRC Centre for Molecular and Cellular Biology, Division of Molecular Biology and Human Genetics, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Stellenbosch University, South Africa.
Antimicrob Agents Chemother. 2013 Feb;57(2):827-32. doi: 10.1128/AAC.01541-12. Epub 2012 Dec 3.
Rifampin resistance in clinical isolates of Mycobacterium tuberculosis arises primarily through the selection of bacterial variants harboring mutations in the 81-bp rifampin resistance-determining region of the rpoB gene. While these mutations were shown to infer a fitness cost in the absence of antibiotic pressure, compensatory mutations in rpoA and rpoC were identified which restore the fitness of rifampin-resistant bacteria carrying mutations in rpoB. To investigate the epidemiological relevance of these compensatory mutations, we analyzed 286 drug-resistant and 54 drug-susceptible clinical M. tuberculosis isolates from the Western Cape, South Africa, a high-incidence setting of multidrug-resistant tuberculosis. Sequencing of a portion of the RpoA-RpoC interaction region of the rpoC gene revealed that 23.5% of all rifampin-resistant isolates tested carried a nonsynonymous mutation in this region. These putative compensatory mutations in rpoC were associated with transmission, as 30.8% of all rifampin-resistant isolates with an IS6110 restriction fragment length polymorphism (RFLP) pattern belonging to a recognized RFLP cluster harbored putative rpoC mutations. Such mutations were present in only 9.4% of rifampin-resistant isolates with unique RFLP patterns (P < 0.01). Moreover, these putative compensatory mutations were associated with specific strain genotypes and the rpoB S531L rifampin resistance mutation. Among isolates harboring this rpoB mutation, 44.1% also harbored rpoC mutations, while only 4.1% of the isolates with other rpoB mutations exhibited mutations in rpoC (P < 0.001). Our study supports a role for rpoC mutations in the transmission of multidrug-resistant tuberculosis and illustrates how epistatic interactions between drug resistance-conferring mutations, compensatory mutations, and different strain genetic backgrounds might influence compensatory evolution in drug-resistant M. tuberculosis.
利福平耐药结核分枝杆菌临床分离株的利福平耐药主要是由于细菌变异株中 rpoB 基因 81bp 利福平耐药决定区的突变选择引起的。虽然这些突变在没有抗生素压力的情况下会导致适应性降低，但在 rpoA 和 rpoC 中发现了补偿性突变，可以恢复 rpoB 基因突变的利福平耐药细菌的适应性。为了研究这些补偿性突变的流行病学相关性，我们分析了来自南非西开普省的 286 株耐药和 54 株敏感的临床结核分枝杆菌分离株，该地区是耐多药结核分枝杆菌高发地区。rpoC 基因的 RpoA-RpoC 相互作用区的部分序列分析显示，所有测试的利福平耐药分离株中有 23.5%携带该区域的非同义突变。这些 rpoC 中的推定补偿性突变与传播有关，因为所有具有 IS6110 限制片段长度多态性（RFLP）模式的利福平耐药分离株中，有 30.8%属于公认的 RFLP 簇，携带推定的 rpoC 突变。在具有独特 RFLP 模式的利福平耐药分离株中，这种突变仅存在于 9.4%中（P<0.01）。此外，这些推定的补偿性突变与特定的菌株基因型和 rpoB S531L 利福平耐药突变有关。在携带该 rpoB 突变的分离株中，44.1%也携带 rpoC 突变，而在携带其他 rpoB 突变的分离株中，只有 4.1%携带 rpoC 突变（P<0.001）。我们的研究支持 rpoC 突变在耐多药结核分枝杆菌传播中的作用，并说明了耐药基因的突变、补偿性突变和不同菌株遗传背景之间的上位相互作用如何影响耐多药结核分枝杆菌的适应性进化。
