Helander Ilkka M, Latva-Kala Kyösti, Lounatmaa Kari
VTT Biotechnology and Food Research, PO Box 1501, FIN-02044 VTT, Espoo, Finland.
Institute of Biotechnology, Electron Microscopy, University of Helsinki, PO Box 56, FIN-00014, Finland.
Microbiology (Reading). 1998 Feb;144 ( Pt 2):385-390. doi: 10.1099/00221287-144-2-385.
Polyethyleneimine (PEI), a polycationic polymer substance used in various bioprocesses as a flocculating agent and to immobilize enzymes, was recently shown to make Gram-negative bacteria permeable to hydrophobic antibiotics and to detergents. Because this suggests impairment of the protective function of the outer membrane (OM), the effect of PEI on the ultrastructure of Salmonella typhimurium was investigated. Massive alterations in the OM of PEI-treated and thin-sectioned bacteria were observed by electron microscopy. Vesicular structures were seen on the surface of the OM, but no liberation of the membrane or its fragments was evident. Since a potential mechanism for the action of PEI could be its binding to anionic LPSs on the OM surface, the interaction of PEI with isolated LPSs was assayed in vitro. The solubility of smooth-type LPSs of Salmonella, regardless of the sugar composition of their O-specific chains, was not affected by PEI, nor was that of Ra-LPS (lacking O-specific chains but having a complete core oligosaccharide). PEI strongly decreased the solubility of rough-type LPSs of the chemotypes Rb2 and Re, whereas it had only a weak effect on the abnormally cationic Rb2-type pmrA mutant LPS, suggesting that the negative charge to mass ratio of LPS plays a critical role in the interaction.
聚乙烯亚胺（PEI）是一种聚阳离子聚合物，在各种生物过程中用作絮凝剂和固定酶，最近研究表明它能使革兰氏阴性菌对疏水性抗生素和去污剂具有通透性。由于这表明外膜（OM）的保护功能受到损害，因此研究了PEI对鼠伤寒沙门氏菌超微结构的影响。通过电子显微镜观察到经PEI处理并制成超薄切片的细菌外膜有大量改变。在外膜表面可见泡状结构，但未观察到膜或其片段的释放。由于PEI作用的潜在机制可能是其与外膜表面的阴离子脂多糖（LPS）结合，因此在体外测定了PEI与分离的LPS的相互作用。沙门氏菌光滑型LPS的溶解度，无论其O特异性链的糖组成如何，均不受PEI影响，缺乏O特异性链但具有完整核心寡糖的Ra-LPS的溶解度也不受影响。PEI强烈降低了化学型Rb2和Re粗糙型LPS的溶解度，而对异常阳离子型Rb2型pmrA突变体LPS的影响较弱，这表明LPS的负电荷与质量比在相互作用中起关键作用。
