Technical note: Survey of extracellular and cell-pellet-associated DNA from ‘touch’/trace samples

The goal of this study was to characterize the reproducibility of extracellular and cell pellet associated DNA yields recovered from handled substrates. Results showed that extracellular DNA yields were extremely variable between contributors—ranging between 0 and >10ng—and tended to dwarf cell pellet yields, which varied between 0 and ∼230 pg. DNA yields across multiple samples from the same contributor on different days showed similar levels of variability in both DNA fractions, indicating that extracellular DNA yield is largely influenced by extrinsic and/or environmental factors and is not a contributor-specific attribute. Microscopic surveys of cells from the pellet fraction as well as fingerprints from the same contributor samples were conducted following treatment with fluorescent DNA stain. Nearly all imaged cells exhibited diffuse fluorescence across the cell without discernable evidence of nuclei. This is consistent with the limited nature of DNA recovery from the pellet fraction and the prevalence of extracellular DNA in these samples.