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February 20, 2013
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and candidate method using both the traditional and alternative confirmation procedures, indicating no
1
significant difference between the candidate and reference methods at any of the time points.
2
3
For the low level inoculum, a dPOD
C
value of 0.10 with 95% confidence intervals of (-0.19, 0.37) was
4
obtained between the reference and candidate method samples confirmed using either the traditional or
5
alternative confirmation procedure at all four time points. The confidence intervals obtained for dPOD
C
6
indicated no significant difference between the two methods. A dPOD
CP
value of 0.00 with 95% confidence
7
intervals of (-0.28, 0.28) was obtained between presumptive and confirmed results using either the
8
traditional or alternative confirmation procedure for all four time points. The confidence intervals obtained
9
for dPOD
CP
indicated no significant difference between the presumptive and confirmed results at all four
10
time points.
11
12
Fresh Spinach
13
For fresh spinach test portions, there were 11 confirmed positives the 3M Petrifilm SALX System for both
14
18 and 24 hour primary enrichment samples transferred to RV-R10 and incubated for 24 hours and
15
confirmed following both the traditional and alternative confirmation procedures. For test portions
16
enriched for 18 and 24 hours and transferred to RV-R10 and incubated for 8 hours there were 7 confirmed
17
positives by the alternative confirmation and 11 confirmed positives by the traditional confirmation
18
indicating the presence of 4 false negative results. There were 10 confirmed positives for samples analyzed
19
by the FDA/BAM method. All un-inoculated control samples were negative by both methods. A χ
2
value of
20
0.10 was obtained between the reference method and the candidate method using the traditional
21
confirmation for all four time points. For candidate samples confirmed following the alternative
22
confirmation procedure, a χ
2
value of 0.10 was obtained for samples enriched for either 18 hours or 24
23
hours in the primary enrichment, transferred to RV-R10 and incubated for 24 hours. For candidate samples
24
confirmed following the alternative confirmation procedure, a χ
2
value of 0.90 was obtained for samples
25
enriched for either 18 hours or 24 hours in the primary enrichment, transferred to RV-R10 and incubated
26
for 8 hours. The chi-square values indicate no significant difference between the candidate and reference
27
method at any of the time points. Although there was no statistical significant difference between the
28
number of positive test portions at 8 or 24 hours in RV-R10 (7 positive at 8 hours and 11 positive at 24
29
hours), it is recommended that only 24 hours of secondary enrichment in RV-R10 be used for fresh spinach.
30
Secondary enrichment for 24 hours in RV-R10 significantly reduced the normal background microbial load,
31
allowing the target organism to reach a higher titer and thus making it easier to identify presumptive
32
positive colonies on the 3M Petrifilm SALX Plate.
33
34
For the low level inoculum, a dPOD
C
value of 0. 05 with 95% confidence intervals of (-0.24, 0.33) was
35
obtained between the reference and candidate method samples confirmed using either the traditional or
36
alternative confirmation procedures at all four time points. The confidence intervals obtained for dPODc
37
indicate no significant difference between the two methods. A dPOD
CP
values of 0.00 with 95% confidence
38
intervals of (-0.28, 0.28) was obtained between the presumptive and confirmed results using the
39
alternative confirmation for all four time points and for test portions incubated in the primary enrichment
40
for either 18 or 24 hours and then incubated for a full 24 hours in RV-R10 and confirmed using the
41
traditional method. A dPOD
CP
value of -0.20 with 95% confidence intervals of (-0.28, 0.28) were obtained
42
between the presumptive and confirmed results for test portions incubated in the primary enrichment for
43
either 18 or 24 hours and then incubated for 8 hours in RV-R10. The confidence intervals obtained for all
44
dPOD
CP
values indicated no significant difference between the presumptive and confirmed results at all
45
four time points.
46
47