Forensic Microbiology

The article below is based on a podcast interview with Dr. Jake Robinson. This post contains affiliate links — see my disclosure policy.

Forensic science is a rapidly evolving field that is constantly looking for innovative ways to provide evidence and solve crimes. Forensic microbiology is a relatively new area of research that is showing great potential for advancing this goal. Microbes, including bacteria and fungi, are everywhere, including on our bodies, in the environment, and at crime scenes. Recent advances in technology have enabled scientists to study the human microbiome and explore whether microbial signatures can be used to link individuals to crimes.

This article will examine the various applications of forensic microbiology, including geolocation, trace evidence, and post-mortem interval, and discuss the potential for microbes to revolutionize the field of forensic science. Additionally, an at-home microbiology activity is included at the end to demonstrate the concept of microbial trace evidence that may be left behind at a crime scene.

What is forensic microbiology?

Forensic science is the application of scientific methods to investigate crimes and provide evidence in a court of law. The use of microbes in forensic science is a relatively new area of research that has shown great potential in recent years. Because microbes, such as bacteria and fungi, can be found everywhere, including on our bodies, in the soil, and in the environment, they have the potential to help in many applications in forensic science.

Forensic microbiology is the application of microbiology to help solve crimes. It began in the 1990s with the development of polymerase chain reaction (PCR) technology, which allows scientists to rapidly identify microbes from samples. Around 2000, concerns over bioterrorism led the US government to invest heavily in forensic microbiology to track the sources of biological agents used by terrorists, such as the anthrax bacterium sent in letters investigated in 2001.

Recent technological advances have enabled researchers to study the microbes that live in and on the human body, known as the human microbiome. The Human Microbiome Project conducted an ecological survey of the microbes across the entire human body and sought to determine the roles they play in human health.

Now, it’s cheaper and easier to identify the microbes that make up people’s unique microbiome signatures. So, researchers are exploring whether these signatures can be used to differentiate between people and link them to crimes based on the microbial traces left behind at crime scenes.

Currently, the practical use of microbiome data to connect a person to a crime requires ongoing research to improve the accuracy. With advancing technology and data analysis, though, microbiome data could play a supportive role in connecting a person to a crime in the near future.

As forensic microbiology continues to develop, microbes will be used in new and fascinating applications to help with crime scene investigation.

Applications of forensic microbiology

Applications of forensic microbiology include trace evidence, geolocation, localization through animal microbiomes, and even post-mortem interval. While the accuracy of microbiome identification is high, it is not yet sufficient to be used as the sole evidence in a court of law. Below describes a few of these applications.

Trace Evidence

Microbes can be used as trace evidence. We leave behind microbes everywhere we go, including on objects we touch, such as our mobile phones, keyboards, and toothbrushes. This microbial evidence can be used much like fingerprints to identify individuals based on their unique microbiome signature and link a suspect to a crime scene. The unique microbial community found on a suspect’s belongings can be compared to the microbial community found at the crime scene to determine if the suspect was present.

Geolocation

Another way that microbes can be used in forensic science is through geolocation. Different soils have distinct microbial communities that can be used to determine the location of a crime. For example, if a suspect walks through a soil and has soil on their shoes, the microbes on their shoes can be analyzed to determine the environment where the soil came from. This information can help investigators narrow down the location of the crime and identify potential suspects.

Localization Through Animal Microbiomes

There’s also the concept of localization through animal microbiomes, where a person’s pets or animals they work with could potentially link them to a crime based on the microbes on their body or clothing from the animal.

Post-mortem Interval Estimation

Lastly, microbes can be used in forensic science for estimating post-mortem interval. The time since death is an important piece of information that can help investigators determine when a crime was committed. As a body decomposes, different microbial communities move into the body, causing changes in the body’s ecosystem. This process is known as natural succession. By analyzing the microbial communities found on a body, investigators can estimate the time since death.

The future of forensic microbiology

Microbes have the potential to revolutionize forensic science by providing new and innovative ways to link suspects to crimes and provide valuable information about crime scenes to investigators. While there is still much research to be done in this area, the use of microbes in forensic science is an exciting and promising field.

At-home microbiology activity: Forensic microbiology trace evidence

This activity involves culturing microbes from two items, one cleaned and the other contaminated with microbes, to observe any differences in microbial growth, which can serve as an example of trace evidence that may be left behind at a crime scene.

Materials:

• Two items to culture, one you’ll clean with alcohol wipes, and the other contaminated with microbes from your fingers
• Sterile culture medium (prepare beforehand according to this protocol, use one that you have on hand, or purchase here)
• Sterile swabs
• Petri dishes
• Incubator (optional)

Instructions:

1. Prepare the culture medium. Make sure it is sterile.
2. Choose two items to culture.
3. Clean one item with an alcohol wipe to remove any pre-existing microbes. Leave the other item contaminated with microbes from your fingers.
4. Using a sterile swab, swab the cleaned item and streak the swab onto a labeled petri dish.
5. Then, swab the contaminated item and streak the swab onto a separate labeled petri dish.
6. Seal the petri dishes with tape or parafilm, and incubate them in an incubator (if available). If you do not have an incubator, you can leave the petri dishes out at room temperature.
7. Check the petri dishes for growth of microbes the next day if incubated or after a few days if left at room temperature. Note any differences in microbial growth, such as the number and types of colonies present.

For a deeper dive into forensic microbiology, read Dr. Jake Robinson’s article: Forensic Applications of Microbiomics: A Review

Also, learn more in Dr. Jake Robinson’s book Invisible Friends…