757 / 1195
2
The method is reproducible from laboratory to laboratory.
3
4
None.
5
Well designed
6
Method is easy to use especially for the 25 g sample. However, I am not sure as to why the
Enriched sample for the 125 g sample is not boiled prior to the VIDAS assay. A safety precaution
needs to be in place to alert users of the instrument that untreated samples were loaded on the
instrument.
7
full confirmation of Listeria. A suggested approach is to compare time to a screened negative
compared to determining this result from the cultural method.
Page 7 - lines 27 to 29 (section D (b)), reword to make it clearer that the secondary enrichment is
done from the incubated primary enrichment. For example, line 145, "After the primary enrichment,
transfer a 1 mL aliquot of the ...", or state as two distinct steps with a space between the two steps.
Just for clarity.
Page 9, lines 7 to 11 (section G (a)), allowing for a 72 hour delay in applying the test kit after
incubation is complete. I believe that the Eurofins report was provided to support this statement
(section 2.1.6 of Eurofins report). However it wasn't clear in this report that the comparison
between immediate testing and testing after a 72 hour of refrigeration was done on all samples, nor
is it clear whether this study was done on the larger sample size with the secondary enrichment. If
this information was provided in the Eurofins report, the information wasn't referred to (e.g.,
reference to a table or annex) in section 2.1.6. Further data, information and/or explanation is
needed before allowing for refrigeration of the enriched broth for up to 72 hours before testing.
Page 11, lines 45 to 47 in Discussion - that many labs indicated difficulty in identifying the isolating
colonies from samples when using the reference method, but not from test portions analyzed by the
VIDAS LP method (which uses a different selective agar). This statement could be removed as it
indicates to me that the labs used in the collaborative study were not familiar with the reference
method, which should be a requirement of participating. As well, the statement isn't supported by
the data as the labs succeeded in identifying the same number of positives with Oxford agar, as with
ALOA agar.
General comments on the use of the Reference Method (AOAC OMA 993.12):
- this method has only required steps (none are optional) that include a purification step before
commencing with confirmation steps, gram stain and cell morphology, catalase, motility, hemolysis
and catalase. In addition, for further biochemical confirmation for identify (e.g., Listeria species
determination), carbohydrates, motility agar, CAMP test is required. Descriptions of how the
reference method was performed, including on page 4, lines 24 to 31 (as well as other text further in
the document), do not make it clear that these steps were included.
Further information is required on whether the reference method was followed as written. If not
followed as written, a list of modifications to the method should be stated in the text, along with
supporting data that supports the modifications (equivalency of the modified method to the
published method). If the same modifications were used in the pre-collaborative study, a solution
may be to state that the collaborative study was carried out with a modified AOAC OMA 993.12,
listing the modifications, as approved by the AOAC GR. I wouldn't support simply saying that the
alternate method has been compared to the reference method, if the reference method wasn't
3
21 June 2013