Action mechanism of cationic drugs increasing the permeability of an outer membrane of Gram-negative bacteria

一种阳离子抗生素革兰氏菌素S已知能增加革兰氏阴性细菌外膜的通透性。为了阐明通透性增加的机制，我们首先尝试确定膜内病变的大小。由于通过“渗透保护实验”可以很容易地确定病变的大小，因此我们使用红细胞。我们观察到，随着革兰西菌素s浓度的增加，病变的大小增加，并且我们观察到在膜病变条件下含有磷脂的膜片段的释放。革兰西菌素S使人红细胞由正常的盘状变为圆齿状。我们推测革兰霉素S分子主要聚集在脂质双分子层的外半部，使红细胞变形为生物。大量堆积使膜结构不稳定，同时导致膜碎片的释放和通透性的增强。接下来，我们研究了革兰杀菌素S对金黄色葡萄球菌的作用。此外，在这种情况下，磷脂的释放在一定浓度范围内受到刺激，导致渗透率发生变化。抗生素对大肠杆菌细胞的作用类似，但大肠杆菌细胞的通透性变化不像金黄色葡萄球菌细胞和红细胞那样明显。这里需要注意的是，属于革兰氏阴性菌的大肠杆菌在细胞结构上有外膜。gramicidin S虽然能显著诱导外膜富含脂多糖的释放，但外膜形成的病变大小明显较小。因此，抗生素很难深入细胞质膜，降低了通透性增强。我们在这里只描述了gramicidin S的结果。通过本研究获得的其他结果也已发表（见参考文献）。

A cationic antibiotic gramicidin S is known to increase the permeability of an outer membrane of Gram-megative bacteria. To clarify the mechanism of permeability increase, we tried to determine the size of lesion formed in membrane at first. For this porpose, we used erythrocytes, since the size of lesion could easily be determined by means of "osmotic protection experiment". It was observed that size of lesion increased with increasing the concentration of gramicidin S. Moreover, we observed the release of membrane fragments containing phospholipids under the conditions of membrane lesion. Gramicidin S caused a morphological change in human erythrocytes from normal discoid to crenated form. We supposed that gramicidin S molecules were predominantly accumulated in the outher half of lipid bilayer, deforming the erythrocyte cell into crenature. A large accumulation made the membrane structure unstable, resulting in the release of membrane fragments and the enhancement of permeability simultaneously. Next, we examined the action of gramicidin S on Staphylococcus aureus. Also, in this case, the release of phospholipids was stimulated in a concentration range causing permeability change. The antibiotic acted similarly on Escherichia coli cells, though the permeability change of E. COLI cells was not so dominant as those of S. aureus cells and erythrocytes. Here, it should be noted that E. COLI belonging to Gram-negative bacteria has outer membrane in the cell structure. Although gramicidin S induced markedly the release of lipopolysaccharide rich in the outer membrane, the size of lesion formed in the outer memgrane was significantly small. Thus, the antibiotic was difficult to intrude deeper into the cytoplasmic membrane, decreasing a permeability enhancement. We described here the results of gramicidin S only. Other results obtained through the present study have also been published (see references).