DNA persistence of bite marks on food and its relevance for STR typing

Abstract

In forensic DNA analysis, salivary traces at crime scenes are a promising way to identify a person. However, crime scenes are oftentimes investigated a while after the crime and recovered samples might have been degraded leading to poor PCR amplification. Probably due to decomposition and negative visual impression of spoiled food, bite mark samples make up only a small part of our casework routine. In this study, bite marks on apples and chocolate bars as well as on an inert surface (microscope slide) were stored up to 3 weeks indoors and outdoors during different seasons and analyzed for amylase activity and DNA quantity and quality. The results underlined the stability of human nuclear DNA not only on inert but also on biological surfaces and their forensic usefulness even when bite marks are stored 21 days under adverse but realistic conditions at a crime scene. Overall, amylase activity as well as DNA quantity decreased over time depending on storage environment with a certain inter- and intrapersonal variation. But amylase activity testing was not found to be an appropriate screening tool for further analysis. Apple bite marks resulted in generally higher DNA amounts than chocolate bars and microscope slides. Although mold reduced the DNA quantity, complete STR profiles could be analyzed. High air humidity and cold temperatures were found to act preservative on raw food with high water content but caused loss of information over time for smooth inert surfaces and hygroscopic foods like sweets. Many factors are involved in the stability of DNA in bite marks and its resulting quality and quantity available for an STR analysis. However, since there was a substantial proportion of informative STR profiles even from bite marks stored for 21 days, the results encourage the analysis of those even if their visual appearance seems unfavorable.

Nucleic Acids Persistence—Benefits and Limitations in Forensic Genetics

“…Unfortunately, bite marks are rarely swabbed and sampled for DNA analysis. Pfeifer et al [ 131 ] examined bite marks on apples and chocolate bars and proved that STR analysis is possible after 21 days, even in samples collected from moldy fruit. Mold reduced the amount of amplifiable DNA but did not rule out a successful STR analysis [ 131 ].…”

“…Pfeifer et al [ 131 ] examined bite marks on apples and chocolate bars and proved that STR analysis is possible after 21 days, even in samples collected from moldy fruit. Mold reduced the amount of amplifiable DNA but did not rule out a successful STR analysis [ 131 ]. Earlier studies indicated that saliva DNA could be preserved on bite marks for 16 [ 132 ] and 24 h [ 133 ].…”

Interpol review of forensic biology and forensic DNA typing 2016-2019

“…A study of recovery of STR profiles from bite marks underlined the stability of human nuclear DNA not only on inert surfaces but also on biological surfaces and their forensic usefulness even when bite marks are stored 21 days under adverse but realistic conditions at a crime scene [ 126 ]. Whether it was possible to distinguish social contact from sexual activity was considered by searching for female profiles on the inside of male underpants [ 127 ].…”

About the influence of environmental factors on the persistence of DNA — a long-term study

“…While several studies deal with the possibilities of DNA transfer [e.g., [6][7][8][9], studies on the persistence of DNA are still rare and have mostly been conducted under laboratory conditions [10][11][12][13]. Investigations of outdoor scenarios are mainly limited to restricted conditions [14][15][16][17][18][19]. Especially, the influence of weather on DNA stability is a very rare topic.…”