Kihm D J, Leyer G J, An G H, Johnson E A
Department of Food Microbiology and Toxicology, University of Wisconsin, Madison 53706.
Appl Environ Microbiol. 1994 Oct;60(10):3854-61. doi: 10.1128/aem.60.10.3854-3861.1994.
Listeria monocytogenes was highly resistant to hen egg white lysozyme in whole milk but was sensitive in media and in phosphate buffer. Methods to sensitize the pathogen to lysozyme in milk were investigated. Treatment of whole milk by cation exchange to remove minerals, particularly Ca2+ and Mg2+, slightly promoted inactivation of L. monocytogenes by lysozyme at 4 degrees C over a period of 6 days. Heat treatment (62.5 degrees C for 15 s) strongly sensitized L. monocytogenes to lysozyme in demineralized milk and in MES [2-(N-morpholino)ethanesulfonic acid] buffer. Addition of Ca2+ or Mg2+ to the demineralized milk restored resistance to lysozyme. Cells were more rapidly heat inactivated at 55 degrees C in demineralized milk containing lysozyme, and addition of Ca2+ to the demineralized milk restored the resistance to heat. The results indicate that minerals or mineral-associated components protect L. monocytogenes from inactivation by lysozyme and heat in milk, probably by increasing cell surface stability. The heat treatment of foods containing added lysozyme can probably play a significant role in producing microbiologically safe foods.
单核细胞增生李斯特菌在全脂牛奶中对蛋清溶菌酶具有高度抗性，但在培养基和磷酸盐缓冲液中则较为敏感。研究了使该病原菌对牛奶中溶菌酶敏感的方法。通过阳离子交换处理全脂牛奶以去除矿物质，特别是Ca2+和Mg2+，在4℃下经过6天，略微促进了溶菌酶对单核细胞增生李斯特菌的灭活作用。热处理（62.5℃处理15秒）使单核细胞增生李斯特菌在脱矿质牛奶和MES[2-(N-吗啉代)乙磺酸]缓冲液中对溶菌酶高度敏感。向脱矿质牛奶中添加Ca2+或Mg2+可恢复其对溶菌酶的抗性。在含有溶菌酶的脱矿质牛奶中，细胞在55℃时热灭活速度更快，向脱矿质牛奶中添加Ca2+可恢复其对热的抗性。结果表明，矿物质或与矿物质相关的成分可保护单核细胞增生李斯特菌在牛奶中不被溶菌酶和热灭活，可能是通过增加细胞表面稳定性来实现的。对添加了溶菌酶的食品进行热处理可能在生产微生物安全的食品方面发挥重要作用。
