99D-35 |
|
J. LI1, G. Teaney, L. Tran, S. Meredith, C. Figard, and J. W. Stave. (1) R&D, Strategic Diagnostics Inc., 128 Sandy Dr, Newark, DE 19713 Enrichment of Listeria for immunoassay detection in foods and environmental samples is often a challenge due to the slow growth rate of Listeria cells and overwhelming natural microbial flora. To overcome this challenge, a proprietary formulation, RapidChek® Listeria media, was developed and evaluated. This media was compared with conventional enrichment media, such as buffered Listeria enrichment broth (BLEB), University of Vermont broth (UVM), Demi-Fraser broth, and Fraser broth for growth rate, resuscitation ability and selectivity. A group of 14 different Listeria serotypes/strains were bulk spiked in 14 various foods and environmental sponges at a level of 1-5 cells per sample (25 g, except for sponges), including deli turkey, frankerfur,chicken nuggets, cheese, milk, seafood and salads. After storage at 4oC or –20oC for 3 days, the samples were enriched with two different protocols: 1) RapidChek® method: one step 40hr at 30oC; and 2) Reference method: a two-step 48hr USDA/FSIS or FDA procedure. The enriched samples were tested by streaking on selective agar plates and RapidChek® Listeria lateral flow assay. The results showed that when compared with conventional media, RapidChek® Listeria media has a significantly faster growth rate and stronger resuscitation ability in heated and/or cold stressed pure cultures. It also showed better selectivity against Listeria growth competitors such as Staphylococcus, Enterococcus, and Pseudomonas. A total of 400 samples were tested for each method (n=800). Out of 320 spiked samples tested for each method, RapidChek® Listeria method recovered 254 confirmed positives (79%), while reference method only reported 215 confirmed positives (67%). There is an excellent correlation (99%) between the streaking results and lateral flow assay results. This work demonstrated the superior performance of this media as to the standard media/protocols. The current one-step method has significant advantages in terms of easy to use, labor and cost savings for the enrichment and detection of Listeria in foods and environmental samples.
Handout (.pdf format, 303.3 kb)
Session 99D, Food Microbiology: General
|