Feasibility of a defined microflora challenge method for evaluating the efficacy of foodborne <i>Listeria monocytogenes</i> selective enrichments

作     者：Hitchins, AD Duvall, RE 

作者机构：US FDA Ctr Food Safety & Appl Nutr Washington DC 20204 USA 

出 版 物：《JOURNAL OF FOOD PROTECTION》 (食品保护杂志)

年 卷 期：2000年第63卷第8期

页      面：1064-1070页

核心收录：

学科分类：0832[工学-食品科学与工程（可授工学、农学学位）] 08[工学] 0836[工学-生物工程] 

主　　题：琼脂/化学 细菌学技术 集落计数 微生物 培养基/化学 食品微生物学 单核细胞增生利斯特菌/生长和发育 单核细胞增生利斯特菌/分离和提纯 动物 

摘      要：Comparison of isolation methods for microbial pathogens is complicated by the variable interference caused by the competitive microflora present in test samples such as foods. In principle, using measured amounts of a standard competitor in a defined surrogate food matrix might control the effect of variable interference. This possibility was investigated using Listeria monocytogenes and enrichment broths belonging to the acriflavine-nalidixate selective agent class. Triplicate test sample sets were prepared. Each set consisted of suspensions of variable levels of the standard competitor, Enterococcus faecium strain 111 (approximate to 10 to 10(9) CFU/25 g), mixed with a low constant level (10 to 100 CFU/25 g) of L, monocytogenes. These test samples were enriched at 30 degrees C for 48 h in different selective media and streaked onto selective isolation agars. The input CFU ratio (E. faecium/L. monocytogenes) that permitted a 50% end point L, monocytogenes recovery was 2,2 x 10(6) or higher for the Food and Drug Administration one-step enrichments and 0.8 x 10(6) for the International Standards Organization (ISO) two-step enrichment. These and other results show that this evaluation method is feasible with this class of enrichments. Interestingly, L. monocytogenes could be detected in enrichment cultures at high-input E, faecium/L. monocytogenes ratios even when the enriched samples were plated onto nonselective media. The pinpoint colonies of L, monocytogenes embedded in a confluent lawn of E. faecium 111 were detectable by their contrasting coloration in Henry obliquely transmitted illumination.