Listeria monocytogenes is a foodborne pathogen which is a significant challenge in food production, particularly for ready-to-eat (RTE) products. Incidence of Listeria in food can be reduced by the application of multiple preservative factors or "hurdles", which include acids, water activity and salts. Studying the growth of Listeria in complex foods is often reliant on laborious plate-counting techniques, therefore alternative methodologies are required. In this study we investigated the use of bioluminescence produced by chromosomally integrated genes encoding luciferase and its substrate to determine microbial growth rates in media and complex food matrices. Five Listeria innocua strains, used as a non-pathogenic surrogate for L. monocytogenes, were transformed with plasmid pPL2luxPhelp, resulting in a collection of Lux-tagged strains. Three test matrices (BHI broth, zucchini purée and béarnaise sauce) were adjusted, testing various combinations of pH (4.7-5.3), water activity (0.96 & 0.98) and undissociated acetic and propionic acid concentrations (0-2 mM). Adjusted matrices were inoculated with a cocktail of Lux-tagged strains and growth monitored over time by both bioluminescence and viable plate counts. Specific growth rates were calculated using both the bioluminescence and plate count data and compared. Statistical analysis showed that specific growth rates determined by bioluminescence did not significantly differ from those determined by plate counts (t-test, P > 0.05), while measurements of bias and accuracy showed good agreement between growth rates determined by both methods. Although plate counts remain the method of choice for detection of very low specific growth rates, this study demonstrates the potential of bioluminescence as a rapid alternative to plate counts for determining microbial growth rates in complex foods.

中文翻译：

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评估Lux技术作为确定实验室培养基和复杂食品基质中李斯特菌生长速率的替代方法。

单核细胞增生李斯特菌是一种食源性病原体，对食品生产，尤其是即食（RTE）产品的生产构成重大挑战。可以通过使用多种防腐剂或“障碍”（包括酸，水分活度和盐分）来降低食品中李斯特菌的发生率。研究复杂食品中李斯特菌的生长通常依赖于费力的盘算技术，因此需要替代方法。在这项研究中，我们研究了编码荧光素酶及其基质的染色体整合基因产生的生物发光在培养基和复杂食品基质中的微生物生长速率的确定。用质粒pPL2luxPhelp转化了五种用作单核细胞增生李斯特氏菌的非致病性替代的无毒李斯特菌菌株，从而得到了带有Lux标签的菌株。调整了三种测试基质（BHI肉汤，西葫芦泥和贝纳酱），测试了pH（4.7-5.3），水活度（0.96＆0.98）和未解离的乙酸和丙酸浓度（0-2 mM）的各种组合。用Lux标签菌株的混合物接种调整后的基质，并通过生物发光和活板计数随时间监测生长。使用生物发光和平板计数数据计算比生长速率并进行比较。统计分析表明，通过生物发光确定的特定增长率与通过平板计数确定的增长率没有显着差异（t检验，P> 0.05），而偏差和准确性的测量结果表明，两种方法确定的增长率之间具有良好的一致性。