Alternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in Staphylococcus aureus.
Alternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in Staphylococcus aureus.
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DOI：
10.1128/mbio.00358-17
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发表时间：
2017-06-20
期刊：
影响因子：
6.4
通讯作者：
Hughes D
中科院分区：
文献类型：
--
作者：
Cao S;Huseby DL;Brandis G;Hughes D
已知金黄色葡萄球菌会产生对氨基糖苷类抗生素具有耐药性的小菌落变异体（SCV），并可导致持续性和复发性感染。SCV的表型是不稳定的，补偿性突变导致恢复生长，通常伴随着抗性的丧失。然而，通过避免抗生素耐药性丧失的机制来改善生长的进化知之甚少。通过连续传代的选择，我们分离并表征了不同类型的基因外抑制突变，这些突变弥补了小菌落变体的缓慢生长。补偿通过两种不同的旁路机制发生：（i）突变体tRNA、核糖体蛋白S5或释放因子2对初始SCV突变的翻译抑制，和（ii）引起SrrAB全局转录调控系统的组成性激活的突变。虽然通过翻译抑制的补偿增加了生长速率，但它也降低了抗生素敏感性，从而恢复了假野生型表型。相比之下，通过激活SrrAB补偿SCV表型的进化途径增加了生长速率而不丧失抗生素抗性。RNA序列分析显示，激活SrrAB途径的突变导致参与肽转运和丙酮酸发酵途径以产生ATP和NAD+的基因上调，从而解释了生长增加。通过增加SCV的生长速率而不丧失氨基糖苷类耐药性，通过SrrAB活化途径的代偿性进化代表了对葡萄球菌感染的有效抗生素治疗的威胁。金黄色葡萄球菌的小菌落变体（SCV）是一个重要的临床问题，其引起持续性和耐药性感染。然而，SCV是不稳定的，可以迅速进化出生长补偿突变体。以前的数据表明，生长补偿只发生在抗生素耐药性丧失的情况下。我们使用连续传代的选择来揭示SCV可获得的四种不同的生长补偿途径。这些途径中的三种（回复、基因内抑制和翻译抑制）以丧失抗生素抗性为代价增加生长。第四条途径激活另一种转录程序，并允许细菌产生支持更快生长所需的额外ATP，而不会失去抗生素抗性。这项工作的重要性在于，它表明耐药SCV可以在不失去抗生素耐药性的情况下进化得更快。
Staphylococcus aureus is known to generate small colony variants (SCVs) that are resistant to aminoglycoside antibiotics and can cause persistent and recurrent infections. The SCV phenotype is unstable, and compensatory mutations lead to restored growth, usually with loss of resistance. However, the evolution of improved growth, by mechanisms that avoid loss of antibiotic resistance, is very poorly understood. By selection with serial passaging, we isolated and characterized different classes of extragenic suppressor mutations that compensate for the slow growth of small colony variants. Compensation occurs by two distinct bypass mechanisms: (i) translational suppression of the initial SCV mutation by mutant tRNAs, ribosomal protein S5, or release factor 2 and (ii) mutations that cause the constitutive activation of the SrrAB global transcriptional regulation system. Although compensation by translational suppression increases growth rate, it also reduces antibiotic susceptibility, thus restoring a pseudo-wild-type phenotype. In contrast, an evolutionary pathway that compensates for the SCV phenotype by activation of SrrAB increases growth rate without loss of antibiotic resistance. RNA sequence analysis revealed that mutations activating the SrrAB pathway cause upregulation of genes involved in peptide transport and in the fermentation pathways of pyruvate to generate ATP and NAD+, thus explaining the increased growth. By increasing the growth rate of SCVs without the loss of aminoglycoside resistance, compensatory evolution via the SrrAB activation pathway represents a threat to effective antibiotic therapy of staphylococcal infections. Small colony variants (SCVs) of Staphylococcus aureus are a significant clinical problem, causing persistent and antibiotic-resistant infections. However, SCVs are unstable and can rapidly evolve growth-compensated mutants. Previous data suggested that growth compensation only occurred with the loss of antibiotic resistance. We have used selection with serial passaging to uncover four distinct pathways of growth compensation accessible to SCVs. Three of these paths (reversion, intragenic suppression, and translational suppression) increase growth at the expense of losing antibiotic resistance. The fourth path activates an alternative transcriptional program and allows the bacteria to produce the extra ATP required to support faster growth, without losing antibiotic resistance. The importance of this work is that it shows that drug-resistant SCVs can evolve faster growth without losing antibiotic resistance.