Methods to be Reviewed by OMB in 2016

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438 Crowley et al.: Journal of AOAC International Vol. 97, No. 2, 2014
laboratory are presented in Tables 2A–D, and Figures 1A–D and
2A–D as supplemental data on J. AOAC Int. website.
Queso Fresco (25 g Test Portions)
Queso fresco test portions, inoculated at a low and high
levels, were analyzed for the detection of Listeria spp.
(Table 3). Uninoculated controls were included in each sample
set. Fourteen laboratories participated in the analysis of this
matrix, and the results of 13 laboratories were included in
the statistical analysis. Laboratory 11 reported data for eight
reference method test portions (including seven uninoculated
control test portions) that produced doubtful profiles of L. grayi.
Colonies on these plates were also reported as beta-hemolytic,
a characteristic not associated with L. grayi. The selective
agar plates for these test portions were sent to the coordinating
laboratory for further examination. Colonies present on the
plates did not possess characteristics typical of Listeria spp.
Colonies were identified as Gram-positive rods containing
spores with morphology typical of Bacillus species. Based on
the preliminary biochemical tests conducted, the test portions
should not have been carried through for final biochemical
identification on API Listeria strips, which resulted in the
misidentification of the test portion as Listeria spp. The results
for this laboratory were excluded from statistical analysis.
The MPNs obtained for this matrix, with 95% confidence
intervals, were 0.63 CFU/test portion (0.49, 0.79) for the
low-inoculum level and 5.48 CFU/test portion (3.60, 8.36)
for the high-inoculum level. For VIDAS LPT test portions, no
differences were observed between confirmation of samples
using the proprietary chromogenic ALOA and the reference
method agar.
For the high-inoculum level, 156 out of 156 test portions
were reported as positive by the VIDAS LPT method with all
test portions confirming positive. For the low-inoculum level,
80 out of 156 test portions were reported as positive by the
VIDAS LPT method with 78 test portions confirming positive,
indicating two false-positive results. For the uninoculated
controls, 1 out of 156 samples produced a presumptive positive
result by the VIDAS LPT method with no samples confirming
positive. All three false-positive samples were obtained from
the same laboratory. For test portions analyzed by AOAC
993.12, 156 out of 156 high-inoculum test portions and 76 out
of 156 low-inoculum test portions confirmed positive. For the
uninoculated controls, 0 out of 156 test portions confirmed
positive.
For the low-level inoculum, a dLPODC value of 0.01
(–0.10, 0.13) was obtained between AOAC 993.12 and VIDAS
LPT. The confidence intervals obtained for dLPODC indicated
no significant difference between the two methods. A dLPOD CP
of 0.01 (–0.10, 0.13) was obtained between presumptive and
confirmed VIDAS LPT results for both confirmation procedures.
The confidence intervals obtained for dLPODCP indicated no
significant difference between the presumptive and confirmed
results.
For the high-level inoculum, a dLPODC value of 0.00
(–0.02, 0.02) was obtained between AOAC 993.12 and VIDAS
LPT. The confidence intervals obtained for dLPODC indicated
no significant difference between the two methods. A dLPOD CP
of 0.00 (–0.02, 0.02) was obtained between presumptive and
confirmed VIDAS LPT results. The confidence intervals
obtained for dLPODCP indicated no significant difference
between the presumptive and confirmed results. Results of
the POD statistical analysis are presented in Table 2013.10A,
Tables 2A–B, and Figures 1A–D, as supplemental data on
the J. AOAC Int. website.
Queso Fresco (125 g Test Portions)
Queso fresco test portions were inoculated at a low and
high level and analyzed for the detection of Listeria spp.
(Table 4). Uninoculated controls were included in each sample
set. Fourteen laboratories participated in the analysis of this
matrix, and the results of 12 laboratories were included in the
statistical analysis. Laboratory 2 did not report any data for
this matrix. Laboratory 11 reported 10 reference method test
portions (including five uninoculated control test portions) that
produced non-L. monocytogenes profiles, with five of the test
portions producing doubtful profiles of L. grayi. Colonies on
these plates contained one or more of the following biochemical
reactions not typically associated with L. monocytogenes:
Gram-negative, non-beta-hemolytic, and catalase negative.
Based on the preliminary biochemical tests conducted, the
test portions should not have been carried through for final
biochemical identification on API Listeria strips which
resulted in the misidentification of the test portion as Listeria
spp. The selective agar plates for these test portions were sent
to the coordinating laboratory for further examination. The
coordinating laboratory confirmed the supplementary results
(Gram stain, hemolysis, and catalase reaction) reported by
the participating laboratory and were not able to identify any
Listeria species. The results from this laboratory were excluded
from statistical analysis. The MPN levels obtained for this test
portion, with 95% confidence intervals, were 0.59 CFU/test
portion (0.46, 0.74) for the low level and 5.41 CFU/test portion
(3.53, 8.30) for the high level. For VIDAS LPT test portions,
no differences were observed between confirmation of samples
using the proprietary chromogenic ALOA and the reference
method agar.
For the high level, 144 out of 144 test portions were reported
as positive by the VIDAS LPT method with all test portions
confirming positive. For the low level, 70 out of 144 test portions
were reported as positive by the VIDAS LPT method with
all 70 test portions confirming positive. For the uninoculated
controls, 0 out of 144 samples produced a presumptive positive
result by the VIDAS LPT method and no samples confirming
positive. For test portions analyzed by AOAC 993.12, 144 out
of 144 high inoculum and 69 out of 144 low inoculum test
Table 2. Heat-stress injury
Matrix Test organism
CFU/OXA
(selective
agar)
CFU/TSA
(nonselective
agar)
Degree
injury, %
Queso fresco L. innocua 5.3 × 108 1.3× 109 59
LPT – 25 g ATCCa 33091
Queso fresco L. monocytogenes 2.9 × 108 9.0× 108 68
LPT – 125 g ATCC 19115
a ATCC = American Type Culture Collection.
Candidates for 2016 Method of the Year
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