Page 136 - 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