单核细胞增多性李斯特菌在体外模拟消化道环境中的抗性

Resistance of Listeria monocytogenes in simulated gastrointestinal systems

摘要:

摘要:【目的】通过测定存活率及细胞内pH(pHi)变化，分析单核细胞增多性李斯特菌(单增李斯特菌)在体外模拟消化道中的抗性。【方法】模拟唾液、胃液和小肠液根据其主要组成成分配制，按试验设计顺次加入后获得模拟的消化道各段混合液(包括相应的pH 及其可能的范围)。平板计数法测定单增李斯特菌在模拟消化液中的存活率，并用荧光比例成像显微镜(fluorescence ratio imaging microscopy，FRIM)测定细菌的pHi。【结果】单增李斯特菌在唾液中存活率＞90%;经pH≤3.0的胃液处理后，其在胃液和胃-肠混合液中的存活率低于0.05%;提高胃液pH至3.5，细菌存活率开始上升;在胃液pH 4.0时，两株单增李斯特菌在模拟胃肠液中存活率显著提高(11.2%－85.9%)。FRIM研究表明，单增李斯特菌在模拟唾液中的pHi与对照组相近。经过pH为3.5和4.0的胃液和胃-肠混合液处理后，pHi值仍维持在较高水平(＞7.75)。【结论】单增李斯特菌在经过pH≥3.5胃液后，能够维持菌体细胞内的pH稳态，且存活率较高，表明其细胞膜仍保持完整。

Abstract:

Abstract:［Objective］Resistance of Listeria monocytogenes was determined through its survival rate and intracellular pH (pHi) after exposed to in vitro digestion models.［Methods］Simulated gastrointestinal systems were prepared according to the major natural components in saliva，gastric juice and contents of the small intestine．Survival of L．monocytogenes was estimated by plate counting and pHi measured via fluorescence ratio imaging microscopy.［Results］L．monocytogenes had a survival rate of over 90% after saliva treatment. Viability was low (less than 0.05%) in gastric juice with pH at or below 3.0 and in the subsequent intestinal fluid. The survival rate started to increase in gastric juice at pH 3.5 and was higher between 11.2%－85.9% for the two tested strains at pH 4.0．The pHi was similar between saliva-treated and untreated bacteria as revealed by fluorescence ratio imaging microscopy. The pHi remained relatively stable at or higher than 7.75 in gastric juice at pH 3.5 and 4.0 or with subsequent introduction of intestinal fluid.［Conclusion］ L．monocytogenes could tolerate gastric juice with pH at or above 3.5 as shown by its good survivability and stable pHi，most probably by maintaining integrity of its membranes.