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SUBMITTED 050113
The inclusivity and exclusivity strains were randomized and divided into blocks for testing as follows.
112 inclusivity strains were listed in an Excel spreadsheet followed by 38 exclusivity strains. A random
number sequence 1-150 was generated using an on-line program [7] and these numbers laid beside the
individual entries in the strain list. The list was then sorted in numerical order 1-150. This resulted in a
randomized list of strains with inclusivity and exclusivity organisms intermixed. The list was then divided
into blocks of 15 strains for processing in a sequence of 10 experiments. One additional inclusivity strain
was obtained later and was added to one of the last testing blocks.
Test strains were taken from frozen storage, streaked to tryptic soy agar (TSA) to obtain isolated
colonies, and incubated at 36 + 1
o
C for 16-24 h. Isolated colonies were picked and streaked again to TSA
and also to 6
Salmonella
selective differential agar media: hektoen enteric agar (HE), xylose lysine
deoxycholate agar (XLD), and bismuth sulfite agar (BS) as described in the FDA/BAM method [3]; and
brilliant green sulfa agar (BGS), xylose lysine tergitol agar (XLT4), and double-modified lysine iron agar
(DMLIA) as described in the USDA/MLG method [4].All plates were incubated at 35 + 1
o
C for 22-24 h,
consistent with instructions in the FDA/BAM and USDA/MLG reference culture procedures.
Preparation of Test Samples
A representative colony from each of the seven different plateswas picked with an inoculating loop and
resuspended individually in 0.5 mL aliquots of phosphate-buffered saline (PBS). At this stage, the tubes
containing the colony resuspensions were randomized and blind-coded by a second technician, so that
the analyst performing the ANSR assays did not know the identity of individual test samples.
ANSR Testing
ANSR assays were conducted in accordance with the test kit instructions, using 50 µL of the colony
resuspension as sample.
Data Analysis
For both the inclusivity and exclusivity panels, the percent correct results was calculated based on
results scored as positive or negative, corresponding to identification of colonies as “
Salmonella
spp
.
” or
“not
Salmonella
spp
.
”
7