Recovery of environmental human DNA by insects

Emerging use of air eDNA and its application to forensic investigations - A review

Biological material is routinely collected at crime scenes and from exhibits and is a key type of evidence during criminal investigations. Improvements in DNA technologies allow collection and profiling of trace samples, comprised of few cells, significantly expanding the types of exhibits targeted for DNA analysis to include touched surfaces. However, success rates from trace and touch DNA samples tend to be poorer compared to other biological materials such as blood. Simultaneously, there have been recent advances in the utility of environmental DNA collection (eDNA) in identification and tracking of different biological organisms and species from bacteria to naked mole rats in different environments, including, soil, ice, snow, air and aquatic. This paper examines the emerging methods and research into eDNA collection, with a special emphasis on the potential forensic applications of human DNA collection from air including challenges and further studies required to progress implementation.

Up in the air: Presence and collection of DNA from air and air conditioner units

Biological material is routinely collected at crime scenes and from exhibits and is a key type of evidence during criminal investigations. Touch or trace DNA samples from surfaces and objects deemed to have been contacted are frequently collected. However, a person of interest may not leave any traces on contacted surfaces, for example, if wearing gloves. A novel means of sampling human DNA from air offers additional avenues for DNA collection. In the present study, we report on the results of a pilot study into the prevalence and persistence of human DNA in the air. The first aspect of the pilot study investigates air conditioner units that circulate air around a room, by sampling units located in four offices and four houses at different time frames post-cleaning. The second aspect investigates the ability to collect human DNA from the air in rooms, with and without people, for different periods of time and with different types of collection filters. Results of this pilot study show that human DNA can be collected on air conditioner unit surfaces and from the air, with air samples representing the more recent occupation while air conditioner units showing historic use of the room.

Comparison of DNA extraction techniques for the recovery of bovine DNA from fly larvae crops

Forensic entomology aids investigations using insects and is primarily associated with the estimation of post-mortem interval (PMI). Studies have shown that human DNA can be recovered from the crops of fly larvae. While several factors regarding the recovery of human DNA from crops have been studied, DNA extraction methods have not been thoroughly assessed. Determining a method for optimal extraction could aid crime laboratories in implementing DNA extraction from larvae and streamlining future research. Bovine DNA was used as a substitute for human DNA to test several DNA extractions kits. Four DNA extraction kits (Chelex®, PDQeX forensicGEM, EZ1® DNA Investigator, DNeasy® Powersoil® Pro Kit) were evaluated based on the quantity and quality of bovine DNA extracted. Extractions were performed on whole fly larvae and dissected crops. Quantification was performed using real-time PCR (qPCR) on a StepOne™ Real-Time PCR System with SYBR® Green using bovine-specific cytochrome b primers. The quality of extracts was determined by checking for inhibition using commercial qPCR chemistries with an internal PCR control (IPC). When using whole fly larvae, Powersoil® Pro yielded the highest average DNA yield (n = 10, 0.668 ± 0.458 ng/μl), while EZ1® DNA Investigator yielded the highest average with crops (n = 10, 0.605 ± 0.403 ng/μl). Chelex and forensicGEM yielded low amounts of bovine DNA, and its extracts were inhibited, unlike EZ1® and Powersoil® Pro, which have purification steps. Therefore, it is recommended to use EZ1® DNA Investigator coupled with automation on EZ1® Advanced XL to recover DNA from fly larvae crops.