Development of "induces of β-lactam-susceptibility in MRSA (ILSMR)" and elucidaton of the novel regulatory mechanism

为了开发新型有效的抗MRSA感染药物，我们试图阐明“MRSA β-内酰胺敏感诱导剂（ILSMR）”的作用机制和MRSA耐药的新机制。在本研究中，mecA和青霉素结合蛋白2'（PBP 2'）的MRSA，与或不与黄酮孵育，分别通过北方和西方印迹分析的表达。mecA mRNA和蛋白水平无明显变化，表明ILSMR黄酮的作用不依赖于mecA转录系统的调控机制。为了探索ILSMR效应通常表达或抑制的基因，使用从与或不与黄酮一起孵育的MRSA菌株No. 5-10中提取的RNA进行cDNA差异杂交。我们发现26个克隆在目前的实验条件下表达水平发生了一些变化。序列测定和同源性检索结果表明，黄酮类化合物能增强MRSA vraS和vraR基因的表达，与这两个基因相关的双组分信号转导系统可能在诱导MRSA对β-内酰胺类药物敏感性的机制中起重要作用，黄酮类化合物及其衍生物对小鼠MRSA全身感染具有较强的抗感染活性。特别是，在体外没有ILSMR作用的TA 1101表明，通过用二元剂量的物质和β-内酰胺抗生素治疗，小鼠被治愈。有趣的是，当在小鼠感染MRSA之前口服给药TA 1101时，显示出这种治疗效果。

In order to develop novel effective drugs against infectious diseases caused by MRSA, we attempted to elucidate the mechanism of action of "inducers of β-lactam-susceptibility in MRSA (ILSMR)" and the novel mechanism of drug resistance of MRSA. In the present investigation, expression of mecA and that of penicilllin-binding protein 2' (PBP2') of MRSA, incubated with or without flavone, were analyzed by Northern and Western blottings, respectively. There were no change in mecA mRNA and the protein levels, indicating that the action of the ILSMR flavone is independent of the regularoty mechanism of mecA transcription system. To explore genes which are typically expressed or repressed by the ILSMR effect, cDNA differential hybridization was performed using RNAs extracted from MRSA strain No. 5-10 incubated with or without flavone. We found 26 clones which exhibited some changes in the expression levels under the present experimental conditions. Determination of the sequences and the homology search revealed that vraS and vraR expression were enhanced in the presence of flavone and the two component signal trans-duction system associated with the both genes may play an important role in the induction mechanism of β-lactam-susceptibility in MRSA.We also found that flavone and its derivatives were highly active against systemic infections by MRSA in mice. In particular, TA1101 having no ILSMR effect in vitro revealed that mice were cured by the treatment with binary dose of the substance and a β-lactam antibiotic. It is interesting that such a curing effect of TA1101 was shown when it was orally administered before the mice were infected with MRSA.