Comparison of plasmid and genomic DNA calibrants for the quantification of genetically modified ingredients

Abstract

Real-time PCR is the method of choice for the quantification of the genetically modified (GM) content of food. Recent EU Commission recommendations advocate expressing the GM content as the percentage of the number of GM target DNA sequences per target taxon specific sequence. The provision of reference materials certified for their copy number content, for example in the form of plasmids, are hence desirable to fulfil this EU recommendation. An inter-laboratory trial was conducted to compare plasmid DNA to the more traditional genomic DNA approach for quantitative PCR calibration in terms of copy numbers, using the model system of Roundup Ready™ soya. Data was analysed from 48 randomised real-time quantitative PCR plates under conditions of reproducibility across three international laboratories. Results demonstrated that the specific plasmid DNA used in the laboratory trial provided a suitable alternative to genomic DNA for use as a calibrant in GM quantification. In the current investigation, plasmid calibrants gave equal or better performance characteristics in terms of precision and closeness to the expected value, than their genomic equivalents.