Antignac Aude, Tomasz Alexander
The Rockefeller University, New York, NY 10021, USA.
Antimicrob Agents Chemother. 2009 Feb;53(2):435-41. doi: 10.1128/AAC.01099-08. Epub 2008 Nov 17.
The mecA gene, the central determinant of methicillin (meticillin)-resistant Staphylococcus aureus (MRSA), is not native to this bacterial species but may have originated in the animal commensal species Staphylococcus sciuri. All S. sciuri strains carry a close homologue of mecA in the form of pbpD, the genetic determinant of penicillin binding protein 4 (PBP 4) of S. sciuri. Here we describe an experimental system that could be used for additional tests for this proposition. The S. sciuri pbpD gene was cloned into a shuttle plasmid and introduced into methicillin-susceptible S. aureus strain COL-S derived from parental MRSA strain COL from which the resistance cassette staphylococcal cassette chromosome mec was excised. The S. sciuri pbpD determinant was transcribed and translated in the S. aureus transductants producing large amounts of the 84-kDa S. sciuri PBP 4 and was then deposited in the plasma membrane of the host bacterium. Transductants carrying the heterologous S. sciuri pbpD gene exhibited properties typical of those of parental MRSA strain COL, including broad-spectrum, high-level, and homogeneous resistance to structurally different beta-lactams. Antibiotic resistance was dependent on the functioning of S. aureus PBP 2 and was suppressed by the specific regulatory genes mecI and mecR and by inhibitors of an early step in cell wall biosynthesis. S. sciuri PBP 4 was also able to replace the essential physiological function(s) of the native PBP 2 of S. aureus and produce peptidoglycan typical of that of parental MRSA strain COL. Our results provide further support for the proposition that the resistance determinant mecA of MRSA strains has evolved from S. sciuri pbpD.
mecA基因是耐甲氧西林金黄色葡萄球菌（MRSA）的核心决定因素，它并非该细菌物种所固有，而是可能起源于动物共生菌松鼠葡萄球菌。所有松鼠葡萄球菌菌株都携带mecA的一个紧密同源物，其形式为pbpD，即松鼠葡萄球菌青霉素结合蛋白4（PBP 4）的遗传决定因素。在此，我们描述了一个可用于对这一命题进行额外测试的实验系统。将松鼠葡萄球菌pbpD基因克隆到穿梭质粒中，并导入对甲氧西林敏感的金黄色葡萄球菌菌株COL-S，该菌株源自亲本MRSA菌株COL，其耐药盒葡萄球菌盒式染色体mec已被切除。松鼠葡萄球菌pbpD决定因素在金黄色葡萄球菌转导子中进行转录和翻译，产生大量84 kDa的松鼠葡萄球菌PBP 4，然后沉积在宿主细菌的质膜中。携带异源松鼠葡萄球菌pbpD基因的转导子表现出亲本MRSA菌株COL典型的特性，包括对结构不同的β-内酰胺类抗生素具有广谱、高水平和均匀的耐药性。抗生素耐药性取决于金黄色葡萄球菌PBP 2的功能，并受到特异性调节基因mecI和mecR以及细胞壁生物合成早期步骤抑制剂的抑制。松鼠葡萄球菌PBP 4也能够替代金黄色葡萄球菌天然PBP 2的基本生理功能，并产生亲本MRSA菌株COL典型的肽聚糖。我们的结果为MRSA菌株的耐药决定因素mecA是从松鼠葡萄球菌pbpD进化而来这一命题提供了进一步支持。
