Transfer and persistence of microbiota markers from the human hand to the knife: A preliminary study

Abstract

New scientific techniques and methods are always needed to link the perpetrators to the incident or the crime scene. Recent microbiota studies based on NGS (Next-generation sequencing) show that various biological samples from crime scenes have the potential to be used in forensic investigations. Especially when DNA traces belonging to more than one person are insufficient to fully determine the genetic profile, a secret sample, such as a microbiota sample created by the suspect's touch, can be used. In this preliminary study, a fictionalized experimental model was designed to investigate the transfer and persistence of the hand microbiome on the knife handle, which has a high potential to be used in criminal incidents, by metagenomic analysis methods. In addition, it was aimed to determine the transfer of specific bacterial species identified only to the person among the five participants onto the knife handle and their persistence over time. In the first stage of the research, samples were collected from the hands of 5 volunteer participants using the swap method, including their palms. Then, after each participant held a different knife, samples were collected from the knife handles via swabs from different angles of the knives at 4 and 24 h and analyzed by metagenomic methods. The findings of this preliminary study showed that the heatmap graphs generated after UniFrac distance analysis were not successful in establishing any similarity between the hand samples and the post-transfer knife handle samples. Nonetheless, it was observed that the transfer of bacterial species detected in the hand samples to knives differed according to the individuals and some bacterial species were transferred to the knife samples held by the participants. The number of bacterial species detected that are specific to each participant's hand sample was 302 in total, and it was determined that a total of 8.28 % of these bacterial species were transferred to the knife handle samples of the 4th hour and 6.95 % to the knife samples of the 24th hour. In the presented study, considering the transfer of some bacterial species in the hand microbiome, which are effective in the variation between individuals, onto the knife; It has been evaluated that some rare bacterial species can be important potential markers to associate the object with the perpetrator.