Helander I M, Nurmiaho-Lassila E L, Ahvenainen R, Rhoades J, Roller S
VTT Biotechnology and Food Research, Espoo, Finland.
Int J Food Microbiol. 2001 Dec 30;71(2-3):235-44. doi: 10.1016/s0168-1605(01)00609-2.
The mode of antimicrobial action of chitosan (polymeric beta-1,4-N-acetylglucosamine) on gram-negative bacteria was studied with special emphasis on its ability to bind to and weaken the barrier function of the outer membrane (OM). Chitosan (250 ppm) at pH 5.3 induced significant uptake of the hydrophobic probe 1-N-phenylnaphthylamine (NPN) in Escherichia coli, Pseudomonas aeruginosa and Salmonella typhimurium. The effect was reduced (E. coli, salmonellae) or abolished (P. aeruginosa) by MgCl2. No NPN uptake was observed during exposure of the salmonellae to chitosan at pH 7.2. Chitosan also sensitized P. aeruginosa and the salmonellae to the lytic effect of sodium dodecyl sulfate (SDS); such sensitization was not blocked by MgCl2 and was reversible by washing chitosan-treated cells prior to SDS exposure. Chemical and electrophoretic analyses of cell-free supernatants of chitosan-treated cell suspensions showed that interaction of chitosan with E. coli and the salmonellae involved no release of lipopolysaccharide (LPS) or other membrane lipids. However, chitosan rendered E. coli more sensitive to the inhibitory action of dyes and bile acids used in selective media. Highly cationic mutants of S. typhimurium were more resistant to chitosan than the parent strains. Electron microscopy showed that chitosan caused extensive cell surface alterations and covered the OM with vesicular structures. Chitosan thus appeared to bind to the outer membrane, explaining the loss of the barrier function. This property makes chitosan a potentially useful indirect antimicrobial for food protection.
研究了壳聚糖（聚合β-1,4-N-乙酰葡糖胺）对革兰氏阴性菌的抗菌作用模式，特别强调了其结合并削弱外膜（OM）屏障功能的能力。在pH 5.3条件下，250 ppm的壳聚糖可诱导大肠杆菌、铜绿假单胞菌和鼠伤寒沙门氏菌对疏水探针1-N-苯基萘胺（NPN）的显著摄取。MgCl2可降低（大肠杆菌、沙门氏菌）或消除（铜绿假单胞菌）这种作用。在pH 7.2条件下，沙门氏菌暴露于壳聚糖期间未观察到NPN摄取。壳聚糖还使铜绿假单胞菌和沙门氏菌对十二烷基硫酸钠（SDS）的裂解作用敏感；这种敏感性不受MgCl2的阻断，并且在SDS暴露前洗涤经壳聚糖处理的细胞可使其逆转。对经壳聚糖处理的细胞悬液的无细胞上清液进行化学和电泳分析表明，壳聚糖与大肠杆菌和沙门氏菌的相互作用不涉及脂多糖（LPS）或其他膜脂的释放。然而，壳聚糖使大肠杆菌对选择性培养基中使用的染料和胆汁酸的抑制作用更敏感。鼠伤寒沙门氏菌的高阳离子突变体比亲本菌株对壳聚糖更具抗性。电子显微镜显示，壳聚糖导致广泛的细胞表面改变，并用囊泡结构覆盖外膜。因此，壳聚糖似乎与外膜结合，这解释了屏障功能的丧失。这一特性使壳聚糖成为一种潜在有用的用于食品保护的间接抗菌剂。
