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Ruggedness Study
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Methodology
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Three parameters were examined to determine the ruggedness of the VIDAS LMX assay: sample boiling time, sample temperature
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after boiling and time of temperature equilibration of reagents.
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Two
Listeria monocytogenes
strains,
Listeria monocytogenes
ATCC 19115 and
Listeria monocytogenes
ATCC 19117 were used as
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positive strains and
Bacillus cereus
ATCC 27522 was used as a non-target strain.
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The two
Listeria monocytogenes
strains were cultivated in LMX broth for 24 hours at 37°C and were diluted to within one log of the
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limit of detection of the kit. The non-target strain was analyzed at the growth level achieved in TSBYE after 24 hours at 37°C
.
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For each method variation, five replicates of each culture were tested simultaneously. This was repeated on 2 occasions over 2 days.
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Sample boiling time
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Replicate samples were placed in boiling water bath for 4 minutes, 5 minutes and 6 minutes then cooled to room temperature.
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Sample temperature
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After boiling replicate samples were placed in a water bath at 10°C, 25°C and 50°C to allow temperature equilibration before
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performing the assay.
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Time of temperature equilibration of reagents at room temperature after pulling from refrigeration
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Reagents were removed from refrigeration and allowed to equilibrate during 0, 30, 60 and 120 minutes at room temperature prior to
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performing the VIDAS assay.
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Results
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Results are presented as Test values and are summarized in Tables 5-7.
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Both
Listeria monocytogenes
strains were positive for all replicates and method variations. The
Bacillus
strain was negative for all
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replicates and method variations. The method variations for all 3 factors showed exact agreement in the number of positive and
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negative results generated. In addition, there was close agreement between the mean test values generated with each method variation.
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PTM Certification Report