Evidence for the evolutionary steps leading to mecA-mediated β-lactam resistance in staphylococci.
Evidence for the evolutionary steps leading to mecA-mediated β-lactam resistance in staphylococci.
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DOI：
10.1371/journal.pgen.1006674
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发表时间：
2017-04
期刊：
影响因子：
4.5
通讯作者：
Miragaia M
中科院分区：
文献类型：
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作者：
Rolo J;Worning P;Boye Nielsen J;Sobral R;Bowden R;Bouchami O;Damborg P;Guardabassi L;Perreten V;Westh H;Tomasz A;de Lencastre H;Miragaia M
流行病学上最重要的金黄色葡萄球菌抗生素耐药机制与mecA相关，mecA是一种获得性基因，编码一种对几乎所有β-内酰胺类抗生素都具有低亲和力的额外青霉素结合蛋白（PBP 2a）。将mecA导入S.金黄色葡萄球菌染色体的突变导致了耐甲氧西林链球菌的出现。金黄色葡萄球菌（MRSA）大流行，导致全球高死亡率。然而，关于mecA的起源和进化知之甚少。不同的mecA同源物已在属于代表最原始葡萄球菌的松鼠葡萄球菌组的物种中鉴定。在这项研究中，我们旨在确定这些mecA前体与β-内酰胺耐药基因mecA和耐药表型之间的进化步骤。我们对106个S. sciuri，S. vitulinus和S. fleurettii菌株，并确定其苯唑西林敏感性谱。对核心基因组进行单核苷酸多态性（SNP）分析，以评估分离株的遗传相关性。通过核苷酸/氨基酸序列比对实现mecA基因同源物和启动子的系统发育分析，并使用贝叶斯分析估计突变率。此外，预测结构的mecA同源物编码的苯唑西林敏感和耐药菌株的PBPs进行了比较。本研究首次发现苯唑西林耐药菌株在沙门氏菌中存在。sciuri集团已经出现了多次，并通过各种不同的机制。耐药性的发展是通过几个步骤发生的，包括天然PBPs非结合结构域的结构多样化; mecA同源物启动子的变化; SCCmec的获得和细菌遗传背景的适应。此外，我们的研究结果表明，正是在人类创造的环境中暴露于β-内酰胺，才推动了天然PBPs向耐药决定簇的进化。葡萄球菌中β-内酰胺耐药性的演变突出了细菌适应抗生素选择压力的众多资源。葡萄球菌中mecA介导的β-内酰胺耐药性的出现和上升一直是全球科学和医学界最关注的问题之一。然而，关于mecA基因决定簇的起源知之甚少。在这项研究中，我们证明了人类环境和牲畜使用的食品添加剂中的抗生素压力是β-内酰胺类抗生素耐药性进化和传播的主要驱动力。此外，我们证实了以前的研究结果表明，通过参与细胞壁合成的天然青霉素结合蛋白的多样化，耐药性的发展发生在葡萄球菌的原始种。我们还表明，通过四种不同的机制实现了耐药性：在蛋白质的特定结构域中的取代的积累;基因启动子的多样化; SCCmec的获得和遗传背景的适应。我们的研究结果突出了原始细菌在不断变化的环境中茁壮成长的资源，这种环境导致了耐甲氧西林金黄色葡萄球菌（MRSA）的大流行。
The epidemiologically most important mechanism of antibiotic resistance in Staphylococcus aureus is associated with mecA–an acquired gene encoding an extra penicillin-binding protein (PBP2a) with low affinity to virtually all β-lactams. The introduction of mecA into the S. aureus chromosome has led to the emergence of methicillin-resistant S. aureus (MRSA) pandemics, responsible for high rates of mortality worldwide. Nonetheless, little is known regarding the origin and evolution of mecA. Different mecA homologues have been identified in species belonging to the Staphylococcus sciuri group representing the most primitive staphylococci. In this study we aimed to identify evolutionary steps linking these mecA precursors to the β-lactam resistance gene mecA and the resistance phenotype. We sequenced genomes of 106 S. sciuri, S. vitulinus and S. fleurettii strains and determined their oxacillin susceptibility profiles. Single-nucleotide polymorphism (SNP) analysis of the core genome was performed to assess the genetic relatedness of the isolates. Phylogenetic analysis of the mecA gene homologues and promoters was achieved through nucleotide/amino acid sequence alignments and mutation rates were estimated using a Bayesian analysis. Furthermore, the predicted structure of mecA homologue-encoded PBPs of oxacillin-susceptible and -resistant strains were compared. We showed for the first time that oxacillin resistance in the S. sciuri group has emerged multiple times and by a variety of different mechanisms. Development of resistance occurred through several steps including structural diversification of the non-binding domain of native PBPs; changes in the promoters of mecA homologues; acquisition of SCCmec and adaptation of the bacterial genetic background. Moreover, our results suggest that it was exposure to β-lactams in human-created environments that has driven evolution of native PBPs towards a resistance determinant. The evolution of β-lactam resistance in staphylococci highlights the numerous resources available to bacteria to adapt to the selective pressure of antibiotics. The emergence and rise of mecA-mediated β-lactam resistance in staphylococci has been one of the greatest concerns of the scientific and medical communities worldwide. However, little is known regarding the origin of the mecA gene determinant. In this study we demonstrate that antibiotic pressure in the human environment and in food additives used in livestock was the major driving force of the evolution and spread of resistance to β-lactams. Furthermore, we confirm the previous findings suggesting that the development of resistance occurs in primitive species of staphylococci through diversification of a native penicillin binding protein involved in cell wall synthesis. We also demonstrate that resistance was achieved through four distinct mechanisms: accumulation of substitutions in a specific domain of the protein; diversification of the promoter of the gene; acquisition of SCCmec, and adaptation of the genetic background. Our results highlight the resources that primitive bacteria used to thrive in a changing environment that has led to the methicillin-resistant Staphylococcus aureus (MRSA) pandemics.