Comparison of six commercially available STR kits for their application to touch DNA using direct PCR

With an increase in the application of direct PCR to items of forensic relevance, as well as the array of STR kits available for amplification, the need for a comprehensive investigation into the optimum STR panel for this workflow has arisen. Here we examine the relative STR amplification success of touch DNA on a range of substrates, with surface properties typical of those found in forensic investigation, using six commercially available STR kits: GlobalFiler®, Identifiler® Plus, Identifiler® Direct, VeriFiler™ Plus, Investigator® 24Plex QS, and PowerPlex® 21. We report on the percentage of possible donor alleles amplified per profile, and the number of samples that resulted in informative genetic data (≥12 autosomal alleles). We also include comment on the ease of interpretation of the resulting electropherograms for each of these six STR kits, when applied within a direct PCR workflow. Donors of known shedder status deposited DNA by handling one of five substrates (glass slide, matchstick, insulated wire, circuit board, and a plastic ziplock bag) for 15 s, 15 min post-handwashing with water. Each item was touched in triplicate by each volunteer for amplification with each STR kit resulting in a dataset of 720 samples. The difference in the number of profiles considered to be informative was found to be statistically significant when comparing STR kits (p = 0.0011) and donors (p = 2e-07), but not when considering substrates (p = 0.15). Identifiler® Plus amplification resulted in the highest profile coverage and second highest percentage of informative profiles. VeriFiler™ Plus generated informative profiles in the largest number of samples (94%) with PowerPlex® 21 amplification resulting in the fewest (79%). There was no significant difference between Investigator® 24Plex QS and GlobalFiler® in any empirical consideration; however, baseline noise and artefact presence made Investigator 24PlexQS profiles more difficult to analyse.