In criminal investigations, detectives meticulously gather and analyze evidence such as weapons, biological fluids, footprints, and fingerprints to reconstruct events and identify individuals involved in a crime. This process is rooted in the “principle of exchange,” formulated by French criminologist Edmond Locard in the early 1900s, which states that “every contact leaves a trace.” Traditionally, these traces included visible materials like pollen, sand, and fibers. However, such evidence often lacks direct association with specific individuals.
Recent research published in *Genes* reveals that the bacteria on a person’s skin leave traces on their clothing that can last for months, potentially providing a unique identifier for the wearer.
### Microbial Traces
Imagine a crime scene where an investigator finds a piece of clothing that doesn’t belong to the victim. Traditional evidence like pollen or sand might indicate where the clothing came from, but identifying its owner can be challenging. Skin cells, hairs, and biological fluids are useful, but the unique community of microorganisms on and within a person’s body offers another avenue for identification.
Microbes specific to different body parts can persist for long periods and transfer to other people and environments, making them valuable for forensic investigations. Forensic microbiology, which began in the early 2000s to counter bioterrorism, now helps identify individuals after death, understand their health before death, determine cause and time of death, and trace origins.
### The ‘Touch Microbiome’
Locard’s principle has evolved to include microbiological traces. Researchers are exploring how much of an individual’s microbiome transfers to their surroundings, how long it persists, and which microbes are most useful for identification. They also study potential contamination from other items or environments and the impact of different surfaces on microbial populations.
In 2021, researchers Procopio, Gino, and colleagues introduced the concept of the “touch microbiome,” the unique bacterial populations on individuals’ skin. They demonstrated that these bacteria could transfer to and persist on non-porous surfaces, like glass slides, for up to a month in uncontrolled indoor environments. They also analyzed DNA from long-frozen bodies, identifying specific microbial populations related to the manner of death and decomposition stage, thus improving our understanding of cold cases.
### Tracing T-Shirts
In a recent study, researchers Magni and colleagues focused on identifying individuals from clothing, often collected as evidence at crime scenes. They had two individuals wear cotton T-shirts for 24 hours in Australia, then stored the shirts in a controlled environment for up to six months alongside unworn control items. Samples from both worn and unworn shirts were frozen, shipped to Italy for microbial DNA extraction, and sequenced in the UK.
The results showed distinct and recognizable microbes unique to each individual on the worn clothing. Even after 180 days, the microbiome remained stable on the worn garments. They also observed microbe transfer between worn and unworn items stored nearby.
### Learning More from Clothes
Clothing at crime scenes can provide key evidence, aiding in profiling individuals and revealing indicators of gender, occupation, income, social status, and affiliations. They can also offer clues about the manner of death, crime location, and time since death. This research demonstrates that clothing can provide even more evidence through unique microbiomes, marking a significant advancement in forensic science.
By leveraging the unique microbial signatures left on clothing, forensic scientists can enhance their ability to identify individuals and reconstruct crime scenes, offering a powerful tool in the quest for justice.
