Feasibility of a defined microflora challenge method for evaluating the efficacy of foodborne Listeria monocytogenes selective enrichments.

摘要: Comparison of isolation methods for microbial pathogens is complicated by the variable interference caused competitive microflora present in test samples such as foods. In principle, using measured amounts a standard competitor defined surrogate food matrix might control effect interference. This possibility was investigated Listeria monocytogenes and enrichment broths belonging to acriflavine-nalidixate selective agent class. Triplicate sample sets were prepared. Each set consisted suspensions levels competitor, Enterococcus faecium strain 111 (approximately 10 10(9) CFU/25 g), mixed with low constant level (10 100 g) L. monocytogenes. These enriched at 30 degrees C 48 h different media streaked onto agars. The input CFU ratio (E. faecium/L. monocytogenes) that permitted 50% end point recovery 2.2 x 10(6) or higher Food Drug Administration one-step enrichments 0.8 International Standards Organization (ISO) two-step enrichment. other results show this evaluation method feasible class enrichments. Interestingly, could be detected cultures high-input E. ratios even when plated nonselective media. pinpoint colonies embedded confluent lawn detectable their contrasting coloration Henry obliquely transmitted illumination.