Recruitment of the mecA gene homologue of Staphylococcus sciuri into a resistance determinant and expression of the resistant phenotype in Staphylococcus aureus
Recruitment of the mecA gene homologue of Staphylococcus sciuri into a resistance determinant and expression of the resistant phenotype in Staphylococcus aureus
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DOI：
10.1128/jb.183.8.2417-2424.2001
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发表时间：
2001-04-01
影响因子：
3.2
通讯作者：
Tomasz, A
中科院分区：
文献类型：
--
作者：
Wu, SW;de Lancastre, H;Tomasz, A
耐甲氧西林金黄色葡萄球菌（MRSA）已成为世界范围内医院获得性疾病的主要致病菌。抗性的遗传决定因子mecA不是沙门氏菌的天然基因。金黄色葡萄球菌，但从一个外来物种来源通过一个未知的机制。最近，我们确定了一个密切的同源基因分离的葡萄球菌sciuri，一个分类原始的葡萄球菌物种最常见的啮齿动物和原始哺乳动物。尽管S. sciuri和S.金黄色葡萄球菌、发现松鼠菌株对β-内酰胺类抗生素一致敏感。为了激活S. sciuri是一种耐甲氧西林的衍生物，K1 M200（其甲氧西林的MIC为200 μ g/ml），通过逐步暴露亲本菌株S获得。sciuri K1（甲氧西林MIC为4 μ g/ml）对增加浓度的甲氧西林的作用。来自K1 M200的mecA同源物的DNA测序揭示了在启动子的-10共有序列中引入了点突变：敏感株K1中核苷酸1577处的胸腺嘧啶残基被抗性株K1 M200中的腺嘌呤取代，伴随着转录速率的急剧增加和与制备的单克隆抗体反应的新蛋白质的出现针对青霉素结合蛋白2A（PBP 2A），即，S.金黄色葡萄球菌mecA。将来自K1 M200（克隆到质粒载体中）的mecA转导到甲氧西林敏感的S.金黄色葡萄球菌突变体导致甲氧西林耐药性的显著增加（从4 μ g/ml的甲氧西林MIC增加到12 μ g/ml，最高达50 μ g/ml），出现可通过荧光分析检测的低亲和力PBP，并产生在Western印迹中与PBP 2A的单克隆抗体反应的蛋白质。去除质粒携带的mecA同源物后，抗生素耐药性和蛋白质产物消失。这些观察结果支持了mecA同源物普遍存在于对寄生虫敏感的动物物种S中的主张。sciuri可能是MRSA致病菌株的甲氧西林抗性基因mecA的进化前体。
Strains of methicillin-resistant Staphylococcus aureus (MRSA) have become the most important causative agents of hospital-acquired diseases worldwide. The genetic determinant of resistance, mecA, is not a gene native to S. aureus but was acquired from an extraspecies source by an unknown mechanism. We recently identified a close homologue of this gene in isolates of Staphylococcus sciuri, a taxonomically primitive staphylococcal species recovered most frequently from rodents and primitive mammals. In spite of the close sequence similarity between the mecA homologue of S. sciuri and the antibiotic resistance determinant mecA of S. aureus, S. sciuri strains were found to be uniformly susceptible to beta -lactam antibiotics. In an attempt to activate the apparently "silent" mecA gene of S. sciuri, a methicillin-resistant derivative, K1M200 (for which the MIC of methicillin is 200 mug/ml), was obtained through stepwise exposure of the parental strain S. sciuri K1 (methicillin MIC of 4 mug/ml) to increasing concentrations of methicillin. DNA sequencing of the mecA homologue from K1M200 revealed the introduction of a point mutation into the -10 consensus of the promoter: the replacement of a thymine residue at nucleotide 1577 in the susceptible strain K1 by adenine in the resistant strain K1M200, which was accompanied by a drastic increase in transcription rate and the appearance of a new protein that reacted with monoclonal antibody prepared against the penicillin-binding protein 2A (PBP2A), i.e., the gene product of S. aureus mecA. Transduction of mecA from K1M200 (cloned into a plasmid vector) into a methicillin-susceptible S. aureus mutant resulted in a significant increase of methicillin resistance (from a methicillin MIC of 4 mug/ml to 12 and up to 50 mug/ml), the appearance of a low-affinity PBP detectable by the fluorographic assay, and the production of a protein that reacted in a Western blot,vith monoclonal antibody to PBP2A. Antibiotic resistance and the protein products disappeared upon removal of the plasmid-borne mecA homologue. The observations support the proposition that the mecA homologue ubiquitous in the antibiotic-susceptible animal species S. sciuri may be an evolutionary precursor of the methicillin resistance gene mecA of the pathogenic strains of MRSA.