The Government Chemist Programme, in LGC, has authored a paper outlining the first available control material to help labs check for false positives when policing imports for genetically modified (GM) rice in food products originating from China.
European law requires laboratory tests for all imported rice consignments and there are currently no GM rice varieties approved for use in the EU but reportedly over 25 varieties that may be a source of contamination .
Dr Malcolm Burns, one of the authors of the paper, said, “Testing for unauthorised GM rice is a complex undertaking and we need to be able to provide assurance that we can prove contamination is present beyond reasonable doubt. This is important not only for consumer confidence but also for the courts, regulators and food businesses. A false positive would mean destroying perfectly good rice. The control material we have developed means that for the first time labs can easily check that their work to avoid false positives is on a sound basis.”
An elaborate process is in place to assess the safety of GM food in the EU and give consumers choice over what they eat. All rice consignments imported into the EU from China are tested for the presence of specific molecular markers associated with genetic modification and when detected consignments must be re-dispatched to the country of origin or destroyed.
The P-35S promoter sequence, derived from Cauliflower Mosaic Virus (CaMV), is one of the genetic elements routinely screened for to infer the presence of GM rice. But this sequence is also present in naturally occurring Cauliflower Mosaic Virus, which can infect plants (such as cauliflower and turnip) affecting plant growth, though it is important to point out that it is harmless to humans.
Thus, to ensure that finding the P-35S promoter sequence implies that a consignment is contaminated with unauthorised GM rice, laboratories need to check that it is not a false positive from naturally occurring Cauliflower Mosaic Virus.
Until now there was no straightforward way of verifying that the tests for the natural virus worked properly in the lab, but in this paper Dr Malcolm Burns and colleagues have reported a suitable control material. A specific DNA sequence from CaMV has been synthesised and inserted into a standard plasmid to provide a suitable control and tested using a validated and EU approved real-time PCR assay. The team was successful in amplifying the DNA target in the CaMV plasmid control with a limit of detection of approximately four copies of the plasmid target.
The full paper is now freely available (open access) from the Journal of the Association of Public Analysts (JAPA) at http://www.apajournal.org.uk./index.html
Notes to editors
1. The work was carried out under the Government Chemist Programme in LGC funded by the National Measurement Office.
2. The Government Chemist Programme is available if an analytical dispute arises between a food business and enforcement authorities. A retained portion of the control sample may, in statutorily defined circumstances, be submitted as a technical appeal to the Government Chemist for a definitive investigation, ‘referee analysis’. http://www.governmentchemist.org.uk/Index.aspx
3. Dr Malcolm Burns is available for interview.
4. On 12 January 2012, Commission Implementing Decision 2011/884/EU was adopted, which describes emergency measures regarding unauthorised genetically modified rice in rice products originating from China. All rice consignments imported into the EU from China are subject to testing for the presence of molecular markers and elements often associated with genetic modification. At present there are no genetically modified (GM) rice varieties approved for use in the European Union, and upon detection consignments containing these genetic elements must be re-dispatched to the country of origin or destroyed. The P-35S promoter sequence, derived from Cauliflower Mosaic Virus (CaMV), is one of the genetic elements routinely screened for to infer the presence of GM rice. Guidance in support of the Commission Implementing Decision 2011/884/EU provided by the European Union Reference Laboratory for GMOs in food and feed advocates that appropriate follow on tests be conducted to ensure that the detection of P-35S is not a false positive due to the natural occurrence of CaMV present with the test sample. However, the EURL Guidance does not provide further instruction on what control material can be used to facilitate such a test, creating an analytical void in the correct application of such a test for false positives.
The present study aimed at developing a suitable plasmid control DNA for CaMV. This was analysed alongside appropriate samples that contained P-35S only, using a validated and EU approved real-time PCR assay that could be used as a follow on test for the detection of Chinese GM rice varieties. The assay was successful in amplifying the DNA target in the CaMV plasmid control with a limit of detection of approximately four copies of the plasmid target. All other sample templates that contained just P-35S produced no detectable amplification. This illustrates the use of the CaMV plasmid DNA as an appropriate control material in conjunction with EU approved tests for the detection of false positives arising from the application of the P-35S test for the detection of Chinese GM rice varieties in support of the relevant legislation.
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