342 / 363
440
C
rowley
et al
.
:
J
ournal of
AOAC I
nternational
V
ol
. 97, N
o
. 2, 2014
agar were identical to the results obtained from the OXA agar
specified by AOAC
993.12
. Out of a total of 451
positives
detected by the VIDAS LPT, 448 were confirmed positive using
OXA or ALOA selective agars.
Discussion
No negative feedback was reported to the study directors from
the collaborating laboratories in regards to the performance of
the VIDAS LPT assay or the ALOA chromogenic agar. Many
laboratories indicated difficulty in identifying and isolating
colonies from samples when using OXA plates, but not from
test portions analyzed by the VIDAS LPT method. These results
may be due to the higher selectivity of the ALOA agar to isolate
and differentiate typical
Listeria
colonies from competing
microflora, such as
Bacillus
colonies. The high selectivity of
the proprietary LPT broth, the high background flora, and the
low selectivity of the OXA agar most likely contributed to this
observation, as well.
Table 4. Individual collaborator results for queso fresco
a
(125 g test portions)
VIDAS LPT
b
High-level test portions
Low-level test portions
Uninoculated test portions
Lab 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12
1 + + + + + + + + + + + + – + + – – – – – + + – + – – – – – – – – – – – –
2
c
NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
3 + + + + + + + + + + + + – + + – – – + + – – + + – – – – – – – – – – – –
4 + + + + + + + + + + + + – – – – + – + – + + – + – – – – – – – – – – – –
5 + + + + + + + + + + + + – – + + – – + – – – + + – – – – – – – – – – – –
6 + + + + + + + + + + + + – – + + + – + + – – – – – – – – – – – – – – – –
7 + + + + + + + + + + + + – + – – – + + + – + + + – – – – – – – – – – – –
8 + + + + + + + + + + + + – – + – – + – + + + + + – – – – – – – – – – – –
9 + + + + + + + + + + + + + + + + + – – – – – – – – – – – – – – – – – – –
10 + + + + + + + + + + + + – + + – + + – – + – – + – – – – – – – – – – – –
11
c
+ + + + + + + + + + + + + + + – – – – – – + – + – – – – – – – – – – – –
12 + + + + + + + + + + + + – + + + + – – + – + + + – – – – – – – – – – – –
13 + + + + + + + + + + + + – – – – – + + + + + – + – – – – – – – – – – – –
14 + + + + + + + + + + + + – – – + + – – + – + – + – – – – – – – – – – – –
AOAC
993.12
1 + + + + + + + + + + + + – – – – – + + + + + + + – – – – – – – – – – – –
2
c
NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
3 + + + + + + + + + + + + + – – – – + – + – – + + – – – – – – – – – – – –
4 + + + + + + + + + + + + – + – – – + + + + – – + – – – – – – – – – – – –
5 + + + + + + + + + + + + – + + – + – + + – + – + – – – – – – – – – – – –
6 + + + + + + + + + + + + + + – – – + + + – – – – – – – – – – – – – – – –
7 + + + + + + + + + + + + + – – + – + + + – – – – – – – – – – – – – – – –
8 + + + + + + + + + + + + + – + + + + – – + + – – – – – – – – – – – – – –
9 + + + + + + + + + + + + + – – – – + – + – – + – – – – – – – – – – – – –
10 + + + + + + + + + + + + + + – – – + + + – + – – – – – – – – – – – – – –
11
c
+ + + + + + + + + + + + +
d
+ +
e
+ + +
f
+
f
– – +
f
+ + – – +
f
+
e
– – – – – +
g
+
g
+
f
12 + + + + + + + + + + + + + – – – + + – – – + – + – – – – – – – – – – – –
13 + + + + + + + + + + + + + + + + + + – – – – + – – – – – – – – – – – – –
14 + + + + + + + + + + + + – – + – + – – – – + + + – – – – – – – – – – – –
a
+ =
Listeria
spp. were detected in samples; – =
Listeria
spp. were not detected in sample; NA
laboratory did not participate in this matrix or results
were not received.
b
Confirmed results from OXA and ALOA were identical for each test portion.
c
Results not used in statistical analysis.
d
Result reported as
L. welshimeri.
e
Result reported as
L. innocua.
f
Result reported as
L. grayi.
g
Result reported as
L. ivanovii.
Candidates for 2016 Method of the Year
341