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ird
et al
.:
J
ournal of
AOAC I
nternational
V
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99, N
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3, 2016
673
However, no evidence of physical cause or suspicion of cause
was noted and it was determined that the data would be included
in the statistical analysis.
There were no statistically significant differences between the
3M Petrifilm RAC Plate and SMEDP methods as determined
by the 95% CI of the differences of means at any of the three
contamination levels.
Discussion
No negative feedback was reported to the study directors
from the collaborating laboratories in regards to the performance
of the 3M Petrifilm RAC Plate. Several laboratories indicated
that the colonies were more easily identified on the 3M Petrifilm
RAC plates then on the reference method agar plates due
to “vibrant colony color and intensity” observed during the
evaluation. For the instant NFDM, several laboratories indicated
the 3M Petrifilm RAC plates prevented colonies from producing
spreader colonies, which had occurred on the reference method
agar plates. This allowed for easier enumeration on the 3M
Petrifilm RAC plates than the reference method agar plates.
Additionally, one laboratory indicated, “For laboratories working
with dairy products or with products that contain high levels of
Bacillus
, the RAC plates would provide a significant benefit.”
During the analysis of the pasteurized skim milk, two
laboratories indicated deviations from the approved protocol and
did not submit data for statistical analysis. Laboratory 7 received
their test portions after 48 h from the initial shipment from the
coordinating laboratory. The temperature control indicated that
the samples were outside the acceptable range, however, the
Figure 7. Youden plot for combined mean 3M Petrifilm RAC Plate and SMEDP results for pasteurized skim milk.
Figure 6. Youden plot for combined mean 3M Petrifilm RAC Plate and FDA BAM results for raw easy-peel shrimp evaluated at 35°C.