A multi-target, non-infectious and clonable artificial positive control for routine PCR-based assays.

Positive controls are essential for PCR reliability and are challenging to obtain for rare, exotic and/or emerging pathogens and pose biosafety risks if manufactured using infectious pathogens. Custom synthetic DNA inserts can be designed de novo in tandems of forward and reverse complement priming sequences to be inserted in circular plasmid vectors. To test this concept, artificial positive controls (APCs) for use in PCR were synthesized to contain primer sequences targeting four viruses (Barley yellow dwarf virus, Soilborne wheat mosaic virus, Triticum mosaic virus and Wheat streak mosaic virus) pathogenic to wheat and, as internal control, the plant mitochondrial nad5 gene. Thermodynamics and folding parameters of twenty-four APC inserts were assessed in silico. Two thermodynamically different APCs, designated optimal and sub-optimal, were cloned and tested using end point PCR. The optimal APC had a 100% amplification rate, while only 92% of virus-infected plant tissues, commonly used as reference positive controls, amplified. An array of APC priming sequences from different organisms and/or previously tested primers can be accommodated in a large and flexible number of positive control targets. APCs will streamline and standardize routine PCR, improve reliability and biosafety, and create opportunities for development and commercialization of new synthetic positive control sequences.

Detection and discrimination of members of the family Luteoviridae by real-time PCR and SYBR® GreenER™ melting curve analysis.

This study investigated the suitability of a two step real-time RT-PCR melting curve analysis as a tool for the detection and discrimination of nine species in the plant virus family Luteoviridae, being Soybean dwarf virus [SbDV], Bean leafroll virus [BLRV], Beet chlorosis virus [BChV], Beet mild yellowing virus [BMYV], Beet western yellows virus [BWYV], Cereal yellow dwarf virus-RPV [CYDV-RPV], Cucurbit aphid-borne yellows virus [CABYV], Potato leafroll virus [PLRV] and Turnip yellows virus [TuYV]. Melting temperature and shape of the melting peak were analysed for 68 bp and 148 bp coat protein gene amplicons using SYBR® GreenER™ fluorescent dye. Specific melting peaks with unique melting temperature were observed for the various species of the family Luteoviridae using the 68 bp amplicon, but not with the 148 bp amplicon. Due to the high variability of sequences for some members of this family, different melting temperatures were also observed between different isolates of the species CYDV-RPV and TuYV. Nevertheless, discrimination between species was achieved for SbDV, BLRV, BChV, BMYV, CABYV and either PLRV or BWYV. Melting curve analysis, in this study, is a faster and more discriminatory alternative to gel electrophoresis of end-point PCR products for the detection of Luteoviridae infection.