527 / 1195
Page 7 - lines 14 to 16 (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 8, lines 35 to 37 (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 19 to 21 in Discussion - that many labs indicated difficulty in identifying the isolating coloniies
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 29 to 36 (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 carried out as validated and published.
- the reference method requires a purification step before analysis is carried on the isolate. If not done,
information on what basis the colonies on agar were called negative for Listeria spp. would be required to
determine if False Negatives by the reference method could have resulted from a mixed colony.
Reviewer #
9.
Pros/Strengths of the Manuscript:
1
Clarity of thought, scientifically sound and accuracy of conclusions
2
Manuscript clearly written.
3
The method shows to have a very good performance.
4
No comments.
5
well written
6
The data tables provide detailed statistical analysis information.
7
Well written, easy to follow.
Reviewer #
10. Cons/Weaknesses of the Manuscript:
1
None
3
21 June 2013