DNA typing from handled items

Abstract

To develop in house protocol for DNA analyses of contact traces, we conducted a series of experiments using low copy number (LCN-PCR) [P. Gill, Application of low copy number DNA profiling, Croatian Med. J. 42(3)(2001) 229–232] amplification of DNA isolated from touched objects. In each experiment, touched objects were swabbed using double swab technique, DNA was extracted by organic extraction protocol, and pooled DNA extracts from both wet and dry swabs were amplified using AmpFlSTR Identifiler kit in 34-cycle PCR. In the first part of this study, seven volunteers held sterile plastic tubes for 10 s, 15 min after washing their hands. From seven tested subjects, we recovered three full and four partial profiles. One of the partial profiles differed from volunteer's reference profile. In the second experiment, volunteers held each other's ankles in order to investigate success of DNA analyses from material transferred by interpersonal skin contact. Mixtures of both persons were obtained from all swabs, and the ratio of each person in the isolate, depended both on shedding status, as well as on hand dominance. The third part of this research tested the effect of the period after the deposition on both quantity and quality of DNA extract. Full DNA profiles were obtained even after 24 h since deposition for two good shedders. In conclusion, LCN-PCR technology provides a valuable approach in DNA typing of trace amounts of biological material, left on even shortly touched objects.