Antibiotic resistant genes and resistant phenotypes in MRSA and VISA strains

描述（由申请方提供）：MRSA和VISA菌株继续对葡萄球菌疾病的治疗提出严重挑战。在社区获得性MRSA中出现了高毒力和流行性谱系，临床文献中继续报告万古霉素治疗失败。对于耐药沙门氏菌所带来的科学挑战，金黄色：虽然已经鉴定了耐药机制的几个关键遗传决定因子，但是在MRSA和VISA菌株中，从耐药基因到抗生素耐药表型的途径仍然是个谜。 MRSA的所有临床分离株携带编码低抗生素亲和力蛋白PBP 2a的相同mecA基因。然而，个别MRSA菌株表现出广泛的苯唑西林MIC值范围，其可以从几微克扩展到毫克范围。此外，大多数MRSA分离株显示出独特的异质表型：这些菌株产生的培养物中，绝大多数细胞（99-99.9%）表现出非常低的MIC值，但相同的培养物还含有一个或多个以低且独特的频率存在的高度耐药细菌亚群。除了提出一个有趣的科学难题，异质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MRSA表型由相同mecA决定子产生的机制尚不清楚。同样，最近通过全基因组测序确定了与获得VISA型万古霉素耐药性相关的遗传决定因素，但VISA菌株JH 9 [2]中鉴定的33种特异性突变产生万古霉素MIC值增加和大量表型改变的机制仍有待确定。因此，在新的研究计划中，MRSA和VISA机制的共同问题是：如何从耐药基因到耐药表型？新研究计划中的研究分为四个主要活动重点。项目A.异源耐药MRSA克隆中高水平抗生素耐药性的遗传决定因素。项目B。遗传和环境因素定义MRSA的抗生素耐药表型。C项目耐甲氧西林金黄色葡萄球菌细胞壁合成途径与耐药水平。D项目万古霉素敏感性降低的遗传途径。

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.