337 / 363
C
rowley
et al
.:
J
ournal of
AOAC I
nternational
V
ol
.
97, N
o
. 2, 2014
435
strips. All of the assay steps are performed automatically
by the instrument. The reaction medium is cycled in and out
of the SPR several times. An aliquot of enrichment broth is
dispensed into the reagent strip. The
Listeria
receptors present
will bind to the interior of the SPR. Unbound components are
eliminated during the washing steps. The proteins conjugated
to the alkaline phosphatase are cycled in and out of the SPR
and will bind to any
Listeria
receptors, which are themselves
bound to the SPR wall. A final wash step removes unbound
conjugate. During the final detection step, the substrate
(4-methyl-umbelliferyl phosphate) is cycled in and out of the
SPR. The conjugate enzyme catalyzes the hydrolysis of the
Table 2013.10B. Summary of results for the detection of
Listeria
spp. in queso fresco (125 g)
Method
a
VIDAS LPT w/OXA
VIDAS LPT w/ALOA
Inoculation level
Uninoculated
Low
High Uninoculated
Low
High
Candidate presumptive positive/total No. of samples
analyzed
0/144
70/144
144/144
0/144
70/144
144/144
Candidate presumptive POD (CP)
0.00
0.49
1.00
0.00
0.49
1.00
(0.00, 0.03)
(0.40, 0.57) (0.97, 1.00)
(0.00, 0.03) (0.40, 0.57)
(0.97, 1.00)
s
r
b
0.00
0.51
0.00
0.00
0.51
0.00
(0.00, 0.16)
(0.46, 0.52) (0.00, 0.16)
(0.00, 0.16) (0.46, 0.52)
(0.00, 0.16)
s
L
c
0.00
0.00
0.00
0.00
0.00
0.00
(0.00, 0.16)
(0.00, 0.12) (0.00, 0.16)
(0.00, 0.16) (0.00, 0.12)
(0.00, 0.16)
s
R
d
0.00
0.51
0.00
0.00
0.51
0.00
(0.00, 0.22)
(0.46, 0.52) (0.00, 0.22)
(0.00, 0.22) (0.46, 0.52)
(0.00, 0.22)
P
value
e
1.0000
0.9730
1.0000
1.0000
0.9730
1.0000
Candidate confirmed positive/total No. of samples
analyzed
0/144
70/144
144/144
0/144
70/144
144/144
Candidate confirmed POD (CC)
0.00
0.49
1.00
0.00
0.49
1.00
(0.00, 0.03)
(0.40, 0.57) (0.97, 1.00)
(0.00, 0.03) (0.40, 0.57)
(0.97, 1.00)
s
r
0.00
0.51
0.00
0.00
0.51
0.00
(0.00, 0.16)
(0.46, 0.52) (0.00, 0.16)
(0.00, 0.16) (0.46, 0.52)
(0.00, 0.16)
s
L
0.00
0.00
0.00
0.00
0.00
0.00
(0.00, 0.16)
(0.00, 0.12) (0.00, 0.16)
(0.00, 0.16) (0.00, 0.12)
(0.00, 0.16)
s
R
0.00
0.51
0.00
0.00
0.51
0.00
(0.00, 0.22)
(0.46, 0.52) (0.00, 0.22)
(0.00, 0.22) (0.46, 0.52)
(0.00, 0.22)
P
value
1.0000
0.9730
1.0000
1.0000
0.9730
1.0000
Positive reference samples/total No. of samples
analyzed
0/144
69/144
144/144
0/144
69/144
144/144
Reference POD
0.00
0.48
1.00
0.00
0.48
1.00
(0.00, 0.03)
(0.39, 0.56) (0.97, 1.00)
(0.00, 0.03) (0.39, 0.56)
(0.97, 1.00)
s
r
0.00
0.51
0.00
0.00
0.51
0.00
(0.00, 0.16)
(0.46, 0.52) (0.00, 0.16)
(0.00, 0.16) (0.46, 0.52)
(0.00, 0.16)
s
L
0.00
0.00
0.00
0.00
0.00
0.00
(0.00, 0.16)
(0.00, 0.12) (0.00, 0.16)
(0.00, 0.16) (0.00, 0.12)
(0.00, 0.16)
s
R
0.00
0.51
0.00
0.00
0.51
0.00
(0.00, 0.22)
(0.46, 0.52) (0.00, 0.22)
(0.00, 0.22) (0.46, 0.52)
(0.00, 0.22)
P
value
1.0000
0.9672
1.0000
1.0000
0.9672
1.0000
dLPOD (C vs R)
0.00
0.01
0.00
0.00
0.01
0.00
(–0.03, 0.03)
(–0.10, 0.13) (–0.03, 0.03) (–0.03, 0.03) (–0.10, 0.13) (–0.03, 0.03)
dLPOD (CP vs CC)
0.00
0.00
0.00
0.00
0.00
0.00
(–0.03, 0.03)
(–0.12, 0.12) (–0.03, 0.03) (–0.03, 0.03) (–0.12, 0.12) (–0.03, 0.03)
a
Results include 95% confidence intervals.
b
Repeatability standard deviation.
c
Among-laboratory standard deviation.
d
Reproducibility standard deviation.
e
P
value = Homogeneity test of laboratory PODs.
Candidates for 2016 Method of the Year
336