AN IMPROVED METHOD TO RECOVER SALIVA FROM HUMAN SKIN - THE DOUBLE SWAB TECHNIQUE

Human bite mark evidence is often found in violent crimes. Due to the difficulties of physically comparing an injury site on elastic and cur ved skin surfaces to the teeth of a suspect, the authors have consider ed using salivary DNA evidence to identify the bite perpetrator. Sever al techniques were evaluated to determine the best method of recoverin g saliva from human skin before extracting genomic DNA from the collec tion substrate. A classical stain recovery technique using a wet cotto n swab was tested against one utilizing a wet filter paper. Additional ly, a new method, referred to as the double swab technique, using a we t cotton swab followed by a dry cotton swab was also evaluated. After recovering a dried saliva stain, DNA was extracted using the modified Chelex method, quantified using the slot-blot procedure, and amplified at three polymorphic loci. The double swab technique showed the highe st percentage recovery of saliva from human skin among the three metho ds studied. This technique is suggested as an improvement over the cla ssical single wet cotton swab technique.