Shimoda M, Ohki K, Shimamoto Y, Kohashi O
Department of Microbiology, Saga Medical School, Japan.
Infect Immun. 1995 Aug;63(8):2886-91. doi: 10.1128/iai.63.8.2886-2891.1995.
Defensins are a family of broad-spectrum antimicrobial peptides found abundantly in the cytoplasmic granules of mammalian neutrophils and Paneth cells of the small intestine. Defensins are known to form ion channels on the membranes of target cells. These channel formations and the cytotoxicity of defensins are intimately linked. We showed the morphological effects of defensins on the cytoplasmic membranes of Staphylococcus aureus by transmission electron microscopy. S. aureus exposed to defensins developed characteristic mesosome-like structures but did not show remarkable changes in cell walls. Defensins induced such structural changes not only at high concentration but also at low concentrations that were not bactericidal. We also showed that increasing the concentration of NaCl in the reaction mixture completely inhibited the occurrence of membranous changes of target cells exposed to defensins. These findings are, to our knowledge, the first report of morphological changes in gram-positive bacteria treated with defensins. Our results indicate that the first effect of defensins in S. aureus is to damage cytoplasmic membranes directly; they also support previous reports that the cell membrane is the principal target of defensins.
防御素是一类广谱抗菌肽，大量存在于哺乳动物嗜中性粒细胞的胞质颗粒以及小肠的潘氏细胞中。已知防御素可在靶细胞膜上形成离子通道。这些通道的形成与防御素的细胞毒性密切相关。我们通过透射电子显微镜观察了防御素对金黄色葡萄球菌细胞质膜的形态学影响。暴露于防御素的金黄色葡萄球菌形成了特征性的类间体结构，但细胞壁未显示出明显变化。防御素不仅在高浓度时，而且在无杀菌作用的低浓度时也能诱导这种结构变化。我们还表明，增加反应混合物中NaCl的浓度可完全抑制暴露于防御素的靶细胞发生膜变化。据我们所知，这些发现是关于用防御素处理革兰氏阳性细菌后形态变化的首次报道。我们的结果表明，防御素对金黄色葡萄球菌的首要作用是直接损伤细胞质膜；它们也支持了先前关于细胞膜是防御素主要靶标的报道。
