Abstract
Bite mark injuries often feature in violent crimes. Conventional morphometric methods for the forensic analysis of bite marks involve elements of subjective interpretation that threaten the credibility of this field. Human DNA recovered from bite marks has the highest evidentiary value, however recovery can be compromised by salivary components. This study assessed the feasibility of matching bacterial DNA sequences amplified from experimental bite marks to those obtained from the teeth responsible, with the aim of evaluating the capability of three genomic regions of streptococcal DNA to discriminate between participant samples. Bite mark and teeth swabs were collected from 16 participants. Bacterial DNA was extracted to provide the template for PCR primers specific for streptococcal 16S ribosomal RNA (16S rRNA) gene, 16S–23S intergenic spacer (ITS) and RNA polymerase beta subunit (rpoB). High throughput sequencing (GS FLX 454), followed by stringent quality filtering, generated reads from bite marks for comparison to those generated from teeth samples. For all three regions, the greatest overlaps of identical reads were between bite mark samples and the corresponding teeth samples. The average proportions of reads identical between bite mark and corresponding teeth samples were 0.31, 0.41 and 0.31, and for non-corresponding samples were 0.11, 0.20 and 0.016, for 16S rRNA, ITS and rpoB, respectively. The probabilities of correctly distinguishing matching and non-matching teeth samples were 0.92 for ITS, 0.99 for 16S rRNA and 1.0 for rpoB. These findings strongly support the tenet that bacterial DNA amplified from bite marks and teeth can provide corroborating information in the identification of assailants.
Highlights
A bite mark is defined as a physical alteration in a medium caused by contact with the teeth [1]
Bite marks can be found in inanimate objects such as foodstuffs, it is injuries inflicted on human tissue that comprise the majority of bite mark cases presented in court [3]
The forensic discipline of bite mark analysis is centered on two assumptions; firstly, that the characteristics of the teeth involved in biting are unique to an individual, and secondly, that this asserted uniqueness is registered in the material that is bitten
Summary
A bite mark is defined as a physical alteration in a medium caused by contact with the teeth [1]. Humans harbour multiple strains of the same Streptococcus species with many strains seemingly unique to individuals [32,33,35] This intraspecies diversity provides the premise that oral streptococci isolated from a bite mark inflicted on human skin may be genotypically matched, with a high degree of assurance, to those from the teeth responsible [20,21]. Should these alternative molecular targets facilitate strain differentiation it may be feasible to utilize them to distinguish between individuals This investigation had two objectives: the first was to apply high throughput sequencing, using the GS FLX 454 technology, to assess the feasibility of matching oral streptococcal DNA sequences amplified from experimental bite marks (inflicted on human skin) to those obtained from the teeth responsible. The second was to evaluate the capability of three genomic regions of streptococcal DNA to discriminate between participant samples
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