2013 ISPAM Mid-Year Mtg Book

BACK GROUND: The qualitative method validation protocol (part 4) for the Compendium of Analytical Methods is in its final revisions and should be published shortly. In this protocol, all methods are evaluated against a standard Compendium method or its equivalent METHODS: For the detection of Salmonella in foods, the following methods are evaluated against MFHPB 20 (Methods for the Isolation and Identification of Salmonella from Foods and Environmental Samples): 1. FSIS (USDA) MLG 4.04, Isolation and Identification of Salmonella from Meat, Poultry, and Egg Products. 2. FDA BAM (Bacteriological Analytical Manual) Chapter 5, Salmonella . 3. AOAC Official Method 2000.06, Detection of Salmonella in Foods with a Low Microbial Load. 4. AOAC Official Method 995.20, Salmonella in Raw, Highly Contaminated Foods and Poultry Feed. 5. AOAC Official Method 967.26, Salmonella in Processed Foods. 6. ISO 6579, Microbiology of Food and Animal Feeding Stuffs- Horizontal Method for the Detection of Salmonella spp. NOTE: All methods have some commodity specific pre-enrichments; however this is not taken into consideration in this comparison. Pre-enrichment: The FSIS (USDA) MLG 4.04 is identical in its use of Buffered Peptone Water (BPW) as the pre-enrichment media and in its incubation conditions to MFHPB 20. The ISO 6579 has the identical pre-enrichment media; however the method has a different incubation temperature and time. Both the USDA and MFHPB 20 pre-enrich at 35 ºC for 20 to 24 hours, where as the ISO 6579 method incubates at 37 ºC for 16 to 20 hours. The difference in the incubation conditions may not be significant enough for the two methods to be unequal. The use of nutrient broth instead of BPW is an option in MFHPB 20. Nutrient broth has been shown to perform as good if not better compared to BPW (D’Aoust, 1991). The pre-enrichment media for the FDA BAM method and the AOAC methods are very different from the methods described previously. All three cultural AOAC methods and the BAM method use Lactose broth or Tryptic Soy Broth (TSB) for their pre-enrichment step. The incubation time and temperature are very close to MFHPB 20. At this time, there is not enough data comparing the use of TSB or Lactose broth to BPW. A literature search only resulted in one article comparing Lactose broth to BPW in a small study. The researcher concluded that more data was needed (Van Schothorst, 1975). At this time there is not a significant amount of data available to compare Lactose broth to BPW, there for the BAM method and the AOAC methods cannot be deemed equivalent to MFHPB 20. Enrichment: The selective enrichment for all the methods is done in the same media. All of the methods under comparison use Tetrathionate broth (TT) along with Rappaport-Vassiliadis (RV) broth. An exception is the ISO 6579 which uses Muller-Kauffmann Tetrathionate Novobiocin (MKTTn) Broth. This broth is very similar to Tetrathionate broth in its selective enrichment principals. MFHPB 20 uses a different naming convention for the two selective broths; TT is named as Tetrathionate Brilliant Green Broth (TBG) and RV is named as Rappaport-Vassiliadis Soya Peptone broth (RVS). The FSIS method uses a different formulation of the RVS broth (mRV), but the formulation is very similar to RV broth. The RV broths in all methods are