Antibiotic resistant genes and resistant phenotypes in MRSA and VISA strains

描述(由申请人提供)：MRSA和VISA菌株继续对葡萄球菌疾病的治疗构成严重挑战。在社区获得性MRSA中出现了高度毒力和流行的谱系，临床文献中仍有万古霉素治疗失败的报道。至于耐药金黄色葡萄球菌带来的科学挑战：虽然已经确定了耐药机制的几个关键基因决定因素，但在MRSA和VISA菌株中，从耐药基因到耐药表型的途径仍然是一个谜。所有临床分离的MRSA都携带相同的mecA基因，编码低抗生素亲和力蛋白PBP2a。然而，个别MRSA菌株的苯唑西林MIC值范围很大，可以从几微克到毫克范围内传播。此外，大多数MRSA分离株表现出特殊的异质性表型：这些菌株产生的培养物中，绝大多数细胞(99-99.9%)的MIC值非常低，但相同的培养物中也包含一个或多个高耐药细菌亚群，这些细菌的出现频率较低且独特。除了提出一个有趣的科学难题外，异种耐药现象也可能具有重要的临床意义，因为体内高耐药亚群的选择可能危及治疗的成功。这些复杂的MRSA表型是由相同的mecA决定簇产生的，其机制尚不清楚。同样，最近通过全基因组测序确定了与获得VISA类型万古霉素耐药性相关的遗传决定因素，但从测序的VISA菌株JH9[2]中确定的33个特定突变产生万古霉素MIC值增加和大量表型变化的机制仍有待确定。因此，在新的研究计划中，对MRSA和VISA机制提出的共同问题是：一个人如何从耐药基因转变为耐药表型？新研究计划中的研究被组织成四个主要的活动焦点。项目A：耐异基因耐甲氧西林金黄色葡萄球菌克隆中高水平抗生素耐药性的遗传决定因素。项目B定义了耐甲氧西林金黄色葡萄球菌耐药表型的遗传和环境因素。项目C：耐甲氧西林金黄色葡萄球菌细胞壁合成途径和耐药水平。项目D降低万古霉素敏感性的遗传途径。

DESCRIPTION (provided by applicant): MRSA and VISA strains continue to present serious challenge to the therapy of staphylococcal disease. Highly virulent and epidemic lineages have emerged among community acquired MRSA and treatment failure during vancomycin therapy continues to be reported in the clinical literature. As to the scientific challenges presented by drug resistant S. aureus: while several critical genetic determinants of the resistance mechanisms have been identified, the path leading from the resistant genes to the antibiotic resistant phenotype has remained an enigma in both MRSA and VISA strains. All clinical isolates of MRSA carry the same mecA gene encoding for the low antibiotic affinity protein PBP2a. Nevertheless, individual MRSA strains exhibit a vast range of oxacillin MIC values which can spread from a few micrograms up to the milligram range. Furthermore, the majority of MRSA isolates show a peculiar - heterogeneous - phenotype: such strains produce cultures in which the great majority of cells (99-99.9%) exhibit very low MIC values but the same cultures also contain one or more sub-populations of highly resistant bacteria which are present with low and unique frequencies. Besides presenting an intriguing scientific puzzle the phenomenon of hetero resistance may have important clinical implications as well, since selection of the highly resistant subpopulations in vivo may jeopardize the success of therapy. The mechanism by which these complex MRSA phenotypes are generated from the same mecA determinant is unknown. Similarly, genetic determinants associated with the acquisition of VISA type vancomycin resistance has been determined recently by full genome sequencing but the mechanism by which the increased vancomycin MIC value and the large number of phenotypic alterations are generated from the 33 specific mutations identified in the sequenced VISA strain JH9 [2] - remains to be determined. Thus, the common question posed for both the MRSA and VISA mechanisms in the new research program is this: how does one go from a resistance gene to the resistant phenotype? The studies in the new research program are organized into four major foci of activity. Project A. Genetic determinants of high level antibiotic resistance in heteroresistant MRSA clones. Project B. Genetic and environmental factors defining the antibiotic resistant phenotype in MRSA. Project C. Pathways of cell wall synthesis and antibiotic resistance level in MRSA. Project D. Genetic pathways to decreased vancomycin susceptibility.