Periodic quality evaluation of DNA from saliva swabs obtained from bite imprints and preserved in ideal and tropical room temperature – A comparative forensic study

Background: Salivary Evidence in a crime scene is scaling revolutionary heights in Forensics. Saliva identification on a victim proves malicious contact, thus carrying more evidentiary weight. Salivary DNA is also a promising tool for epidemiological genomic studies. This study was conducted to investigate state of DNA in scenarios of delayed evidence collection in tropical climatic temperatures. Aim: To evaluate quality of genomic DNA extracted from saliva swabs obtained from bite imprints and to assess the genomic fidelity when the DNA from the dry evidence is preserved in favorable and unfavorable temperatures for a period of 60 days. Materials and Methods: 25 participants were recruited and 2 samples, the first comprising of 5ml of unstimulated saliva and second, bite imprints recorded on putty impression material were obtained. Swabs were taken from the bite imprint on the 1st day simulating early evidence collection and 3rd day simulating delayed evidence collection respectively; the 3 day interval during which bite imprints were left unprotected at room temperature. Single swabbing technique was employed in swab collection. DNA extraction was done from the collected saliva and the swabs to compare quantity and check quality. Extracted Trace DNA was preserved in a range of tropical temperatures and inspected for degradation by PCR once in 20 days, for 60 days. On the 60th day, DNA quality comparison was done. Results: The comparison between quantity of DNA in saliva and swab A showed statistical significance with P=0.0005 <0.001 with the mean±S.D of saliva (87.44±42.05 ) and Quantity of DNA from swab A being (1.53±0.72). Similarly the comparison of Quantity of DNA from saliva and swab B showed significance with P=0.0005<0.001 with swab B ( 0.65±0.30) and the comparison between swab A and Swab B also statistical significant with ( 1.53 ±0.72) and (0.65±0.30) respectively. The Trace genomic DNA which was obtained by portioning Swab B DNA into 3 parts and preserved in unfavorable temperatures exhibited reliable quality within study period which was demonstrated by DNA amplification pattern in Polymerase chain reaction. Conclusion: In delayed Evidence collection upto 3 days, tropical climatic temperature does not seem to hamper the quality of DNA and the genomic fidelity was found to be maintained. The study also proved that Trace Genomic DNA can be preserved in normal tropical temperatures for a minimum of 60 days without the threat of complete DNA degradation.