An Improved Method to Recover Saliva from Human Skin: The Double Swab Technique

Abstract

REFERENCE:Sweet D, Lorente M, Lorente JA, Valenzuela A, Villanueva E. An improved method to recover saliva from human skin: The double swab technique. J Forensic Sci 1997;42(2): 320-322. ABSTRACT:Human bite mark evidence is often found in violent crimes. Due to the difficulties of physically comparing an injury site on elastic and curved skin surfaces to the teeth of a suspect, the authors have considered using salivary DNA evidence to identify the bite perpetrator. Several techniques were evaluated to determine the best method of recovering saliva from human skin before extracting genomic DNA from the collection substrate. A classical stain recovery technique using a wet cotton swab was tested against one utilizing a wet filter paper. Additionally, a new method, referred to as the double swab technique, using a wet cotton swab followed by a dry cotton swab was also evaluated. After recovering a dlied 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 highest percentage recovery of saliva from human skin among the three methods studied. This technique is suggested as an improvement over the classical single wet cotton swab technique.KEYWORDS: forensic science, saliva, bite marks, odontology, serology, forensic evidence Teeth are often used as a weapon in violent crimes when one person attacks another, or in self-defense against an attacker (1). Human bite marks are found in cases of homicide, sexual assault, and crimes of family violence including child and spousal abuse (2). Conventional analysis strategies attempt to physically compare the injury pattern found on the victim's skin to the teeth of the suspected biter to reach conclusions regarding relative concordance (3).In addition to considering bite marks as examples of physical evidence, the authors have also focused their attention on bite ~Forensic odontologist, UBC Faculty of Dentistry, Vancouver, BC Canada.2Assistant professor, associate professors, and professor, respectively, Faculty of Medicine, University of Granada, Spain.This project was supported by grants from the Ministry of Education and Science of the Government of Spain (PB93-1155), the Plan Propio de Investigaci6n of the University of Granada, Spain, and by the Dentistry Canada Fund/Warner Lambert Foundation, Ottawa, Canada.Received 3 June 1996; and in revised form 31 July 1996; accepted on 2 Aug. 1996. marks as biological evidence. It is assumed that forensically significant amounts of saliva are deposited during biting, sucking, or licking and that traces of salivary evidence can be recovered for identity testing.Determination of the origin of a saliva stain using conventional markers is not highly sensitive nor discriminatory. The limited detectability of blood group antigens and polymorphic proteins due to their low concentrations is an inherent problem (4). Genomic DNA testing has increased sensitivity compared with conventional saliva testing methods ...

Relevance of sampling and DNA extraction techniques for the analysis of salivary evidence from bite marks: a case report

“…In addition, despite the use of the single swab technique in this study, the quantity of recovered DNA from the bite marks was sufficient for STR typing. In fact, the difference in the DNA recovering capacity between the single and double swab techniques was only 9.3% (Sweet et al, 1997b), with such a difference not being significant at least in this case.…”

“…The DNA collection was maximized by collecting the saliva from the skin surface using two swabs: the first swab was moistened with sterile distilled water, and the second dry swab, used to collect the moisture remaining on the surface after the first swab. These two swabs are subsequently pooled together into a single sample (Sweet et al, 1997b).…”

The effect of mark enhancement techniques on the subsequent detection of saliva

“…The saliva stains were extracted from both the tiles and envelopes by swabbing the surface of the substrates using a method adapted from Sweet et al [67]. The swab was submerged in sterile distilled water in order to completely wet the tip, which was then rolled over the surface of the substrate.…”

Novel Tissue Types for the Development of Genomic Biomarkers

“…Saliva is an easily obtainable tissue that has been used in forensics for decades (Sweet et al, 1997). However, new molecular profiling kits for voluntary saliva collection have made saliva an increasingly useful clinical biomarker tissue.…”