877 / 1195
Fractional/low
- Samples were inoculated at levels that produced at least one
88
reference method Probability of Detection (POD
R
) or candidate method POD (POD
C
)
89
in the range of 0.25 – 0. 75 (5-15 positive results)
90
0.2
– 2 cfu/ test portion
91
25 replicates
92
High
– Samples were inoculated at levels to assure a POD
C
of nearly 1.00 with as high
93
a degree of confidence as possible
94
5 cfu/ test portion
95
5 replicates
96
Most Probable Number
: The inoculums levels in the artificially contaminated
97
samples were determined by the Determination of the Most Probable Number [MPN]
98
values of target analyte
in the naturally contaminated food lots and the artificially
99
contaminated food lots on the day of initiation of analysis.
100
A 5-tube 3-level MPN was performed on each inoculated food level. The 25 replicate
101
test portions analyzed by the reference methods were used as the middle level for the
102
MPN. Five replicates of a high level using 100 g inoculated matrix and 5 replicates of a
103
low level using 10 g inoculated matrix were prepared by adding reference method
104
enrichment broth to make a 1:10 dilution and following the appropriate reference
105
method until confirmations. The number of positives from the high, medium and low
106
levels was used to calculate the MPN and 95% confidence intervals for each
107
inoculated level of each matrix by using the MPN calculator
108
( http://www.lcfltd.com/customer/LCFMPNCalculator.exe ).
109
110
VIDAS LMX method –
125g test portions for ground meat, soft cheese and deli
111
1.
A 125g test portion of each food matrix was combined with 375 (1:4) mL of
112
LPT broth (at room temperature) into a filter stomacher bag.
113
2.
The sample and the broth were homogenized for 2 min and then incubated
114
at 30 ±1°C for 26 hr.
115
3.
For Secondary transfers: 1 mL of enrichment was transferred into 10 mL
116
LPT broth, and incubated for 22 h at 30°C
117
4.
From each secondary enrichment, 0.25 mL was transferred into the sample
118
well of the
LMX
strip.
119
5.
The LMX strip was not heated and was analyzed on VIDAS.
120
6.
The LMX method was performed following the package insert instructions.
121
122
Validation Study Confirmation:
All test portions, regardless of presumptive result
123
were confirmed using the USDA/FSIS (MLG Ch. 8.07) method for ground beef, deli
124
ham and turkey, and AOAC (section F, b) method for queso fresco.
125
126
127
128
129
PTM Certification Modification Report