Crime Scene Culture: How Inadvertent Collection of Bacteria Affects DNA Profiling Success

The role of a forensic scientist is challenging.  Most of us get into this field because of our desire to have a positive impact, make the world safer, and fight crime through science. We utilize scientific data to help law enforcement identify criminals, exonerate the innocent, and assist in helping to bring closure to victims and their families.


Written by: Manzar Ahmed, Bode technology



Forensic Experience Drives Innovation

Bode Technology is often recognized as a forensic laboratory that processes thousands of cases, but we are unique in that we take what we have learned in the lab to develop new products and solutions. The ability to develop new technologies from the standpoint of experienced scientists has helped us identify needs and create new solutions that truly impact our work.


I started my career at Bode as a casework DNA analyst responsible for processing multiple different types of cases with some of the crimes occurring before I was even born. I experienced firsthand the difficulties degraded samples can cause for profile interpretation and comparison.  I transitioned out of casework to Bode’s Product Development Team where I took that knowledge and focused research on developing tools and methods to enable better collection and preservation of crime scene evidence. Advancements in DNA technology, including the recent phenomenon of forensic genealogy, have highlighted the need for evidence preservation. The evidence that is being collected today may require the technology of tomorrow in order to solve the case.


Crime Scenes: Collecting Much more than Biological Evidence

One of my team’s goals is to develop and improve methods of sample collection and storage that ensure the valuable DNA evidence recovered at a crime scene is preserved while it awaits laboratory analysis. In order to improve the preservation of DNA evidence, we needed to fully understand what composes a crime scene sample. When an investigator or analyst is swabbing an item or sampling at a crime scene, they are trying to collect the cellular material that will provide evidence in the crime. What is often overlooked, and unseen are the microbes present on the evidence item that are collected along with the sample. These microbes can potentially degrade the sample while it is awaiting analysis. Our study specifically looked at trying to quantify, identify, and determine the impact of microbes on mock crime scene samples.


In this study, various mock crime scene materials were either spotted with a known amount of biological fluid (blood) or handled to create touch DNA samples. All samples were subsequently collected with standard cotton swabs and stored in swab boxes under various temperature and humidity conditions to simulate storage in different geographical areas.


Following laboratory processing and analysis, we were able to identify more than 200 different species of bacteria that had been collected along with our blood samples and over 400 species collected along with the samples from the handled items. Individual species of bacteria can have different characteristics, including exhibiting extracellular nuclease activity, which can negatively impact a collected sample. Distinct colonies obtained from our mock evidence were chosen at random and tested for DNase activity, with ~20% yielding positive results.


Impact of Bacteria on the ability to Generate a DNA Profile

The DNA profiling results indicated that each sample and substrate combination was unique in terms of evidence preservation. Depending on the biological material, mock crime scene material, and storage conditions, the DNA profiling success rates were impacted by degradation to varying degrees. For example, five paired blood stains were individually collected from the sole of a worn shoe. Samples that were processed immediately after collection yielded complete profiles whereas samples that were stored for 10 days at room temperature and 40-50% relative humidity yielded 7 times less DNA and common signs of sample degradation (allelic dropout and imbalance) were observed in the DNA profiles. The number of species of bacteria identified, the confirmed extracellular nuclease activity, and the rapid sample degradation highlight the need for evidence collection devices that actively work to prevent microbial impact and degradation.


Solutions Exist to Prevent Degradation of Evidence

Understanding that we will never be able to control the cleanliness of a crime scene, my team is using the data from this study to develop and enhance evidence collection and preservation methods. Bode’s SecurSwab Technology utilizes integrated desiccants to quickly dry a sample and maintain a dry environment which can reduce microbial activity. In the creation of our newest device, the Bode BioSafe Swab, we have combined SecurSwab Technology with a chemically treated swab head to preserve samples at the point of collection. We have developed a solution that inhibits microbial growth and enzymatic activity without impacting downstream processing and analysis.


Impact: Improved Technology leads to Improved Success

Bode’s internal testing results have yielded 30% more complete STR profiles from mock crime scene samples collected with the BioSafe Swab compared to samples collected with standard cotton swabs and stored in swab boxes.


Through interpretation and testimony, DNA can assist in bringing justice for victims, exonerating the innocent, and helping to bring closure to families. To obtain the best DNA results possible, proper evidence collection and storage techniques are important to prevent or inhibit the growth of bacteria and fungi, which can degrade and damage the DNA present in biological materials.


I’ve seen the technology involved in the analysis of DNA from crime scenes advance greatly in my nearly 10 years at Bode. The advancements in expanded loci STR kits and mixture deconvolution software have offered analysts more tools than ever to analyze and interpret data to assist law enforcement. In those same 10 years, the forensic community seems to continue to overlook how that data is obtained.


Without proper evidence collection, storage, and preservation, critical evidence and data may be lost forever before analysis and criminal investigations even begin. While laboratories have focused on implementing downstream technologies to generate better profiles and process cases more effectively, improvements to front end collection are just as important in our efforts to generate usable DNA profiles. Devices utilizing SecurSwab Technology and the BioSafe Swab are solutions that increase a laboratory’s ability to generate data that can support and drive investigations. Bode will continue to pave the way to provide collection devices and methods that actively work to prevent sample degradation.