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ird
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4, 2016
time of 96 h. All raw ground beef samples were packed with cold
packs to target a temperature of <7°C during shipment. Creamy
peanut butter test samples were inoculated 10 days prior to the
shipment. Samples were shipped on a Thursday via overnight
delivery and held at ambient temperature (20–25°C) until the
following Monday when analysis was initiated after a total of
2 weeks of equilibration of the inoculum.
In addition to each of the test portions and a separate APC
sample, collaborators received a test portion for each matrix
labeled as “temperature control.” Participants were instructed to
obtain the temperature of this portion upon receipt of the package,
document the results on the Sample Receipt Confirmation form
provided, and fax or e-mail it back to the study director. The
shipment and hold times of the inoculated test material had been
verified as a QC measure before study initiation.
Test Portion Analysis
Collaborators were instructed to follow the appropriate
preparation and analysis protocol for eachmatrix for the 3MMDA2
–
Salmonella
method and the referencemethods. For bothmatrixes,
each collaborator received 72 test portions (12 high, 12 low, and
12 uninoculated controls for each method to be performed). For
the analysis of the raw ground beef test portions by the 3M MDA
2 –
Salmonella
method, a 325 g portion was enriched with 975 mL
prewarmed (41.5 ± 1°C) ISO BPW, homogenized for 2 min, and
incubated for 10 h at 41.5 ± 1°C. For the creamy peanut butter test
portions analyzed by the 3MMDA 2 –
Salmonella
method, a 25 g
portion was enriched with 225 mL ISO BPW, homogenized for
2 min, and incubated for 18 h at 37 ± 1°C.
After enrichment, samples were assayed by the 3M MDA
2 –
Salmonella
method and, regardless of presumptive result,
confirmed using the appropriate reference method. Both
matrixes evaluated by the 3M MDA 2 –
Salmonella
method
were compared to samples analyzed using either the USDA/
FSIS MLG or FDABAM reference method in an unpaired study
design. All positive test portions were biochemically confirmed
by the API 20E biochemical test (AOAC
Official Method
978.24
; 11) or by the VITEK 2 Gram-negative biochemical
identification test (AOAC
Official Method
2011.17
; 12).
Polyvalent
Salmonella
serological testing was also performed.
Statistical Analysis
Each collaborating laboratory recorded the results for the
reference method and the 3M MDA 2 –
Salmonella
method on
the data sheets provided. The data sheets were submitted to the
study director at the end of each week of testing for statistical
analysis. Data for each test portion size was analyzed using the
probability of detection (POD) statistical model (13). POD was
calculated as the number of positive outcomes divided by the
total number of trials. The POD was calculated for the candidate
presumptive results (POD
CP
), the candidate confirmatory
results (including false-negative results; POD
CC
), the difference
in collaborator POD (dLPOD) in the candidate presumptive
and confirmatory results (dLPOD
CP
), presumptive candidate
results that confirmed positive (excluding false-negative results;
POD
C
), the reference method (POD
R
), and the difference in
the confirmed candidate and reference methods (dLPOD
C
).
A dLPOD
C
confidence interval not containing the value 0
would indicate a statistically significant difference between
the 3M MDA 2 –
Salmonella
and the reference methods at the
5% probability level. In addition to POD, repeatability SD (s
r
),
among-laboratory repeatability SD (s
L
), reproducibility SD
(s
R
), and the homogeneity test of laboratory PODs (
P
T
) value
were calculated. The s
r
provides the variance of data within
one laboratory, the s
L
provides the difference in SD between
laboratories, and the s
R
provides the variance in data between
different laboratories. The
P
T
indicates if adequate sample
homogeneity has occurred between laboratories (14).
AOAC Official Method 2016.01
Salmonella
spp. in Select Foods and
Environmental Surfaces
3M™ Molecular Detection Assay (MDA)
2 –
Salmonella
Method
First Action 2016
(Applicable to detection of
Salmonella
spp. in raw ground
beef (73% lean), raw ground chicken, chicken carcass rinse,
chicken carcass sponge, pasteurized liquid whole egg, cooked
breaded chicken, instant nonfat dry milk, black pepper, cocoa
powder, raw whole shrimp, raw bagged spinach, creamy peanut
butter, dry dog food, pasteurized processed American cheese,
spent sprout irrigation water, and sealed concrete, stainless
steel, and sealed ceramic tile environmental surfaces.)
Caution
: The 3M MDA 2 –
Salmonella
is intended for use in
a laboratory environment by professionals trained in
laboratory techniques. 3M has not documented the
use of this product in industries other than the food
and beverage industries. For example, 3M has not
documented this product for testing drinking water,
pharmaceutical, cosmetics, clinical, or veterinary
samples. The 3MMDA 2 –
Salmonella
has not been
evaluated with all possible food products, food
processes, testing protocols, or with all possible
strains of bacteria.
As with all test methods, the source of enrichment medium
can influence the results. The 3MMDA 2 –
Salmonella
has only
been evaluated for use with the enrichment media specified in
the manufacturers instructions for use.
The 3M MDS instrument is intended for use with samples
that have undergone heat treatment during the assay lysis step,
which is designed to destroy organisms present in the sample.
Samples that have not been properly heat-treated during the
assay lysis step may be considered a potential biohazard and
should not be inserted into the 3M MDS instrument.
The user should read, understand, and follow all safety
information in the instructions for the 3MMDS and the 3MMDA
2 –
Salmonella
. Retain the safety instructions for future reference.
Periodically decontaminate laboratory benches and equipment
(pipets, cap/decap tools, etc.) with a 1–5% (v/v in water)
household bleach solution or DNAremoval solution. When testing
is complete, follow current industry standards for the disposal of
contaminated waste. Consult the Material Safety Data Sheet for
additional information and local regulations for disposal.
To reduce the risks associated with exposure to chemicals
and biohazards, (
1
) perform pathogen testing in a properly
equipped laboratory under the control of trained personnel; (
2
)
always follow standard laboratory safety practices, including
wearing appropriate protective apparel and eye protection
while handling reagents and contaminated samples; (
3
) avoid
contact with the contents of the enrichment media and reagent