When you think of a criminal investigation, detectives meticulously collecting evidence at the scene come to mind: weapons, biological fluids, shoe prints, and fingerprints. But this is only the beginning of the attempt to reconstruct the events and identify the people involved. At the center of the process is the "exchange principle" formulated by the French criminologist Edmond Locard in the 20s: “Every contact leaves a trace”.
Today, new research published on Genes (I link it to you here) brings this principle into the era of forensic microbiology, demonstrating how the bacteria that live on our skin leave unique traces on the clothes we wear. Traces that last for months and can be used to identify us unequivocally.
From visible to invisible traces: the evolution of forensic science
In Locard's time, the traces looked for at crime scenes were typically those visible under a microscope, such as pollen grains, sand and fibres. Useful evidence to reconstruct the dynamics of events, but with a limit: not always associated with a specific individual. Over the years, forensic sciences have tried to overcome this limit, shifting attention to traces increasingly minutely linked to the biological uniqueness of each person: fingerprints, DNA, residues of body fluids.
Today, a new frontier appears on the horizon of every field of investigation: the human microbiome, that is, the set of microorganisms that live on and inside our body. Bacteria, fungi and viruses that accompany us throughout our lives, forming unique and stable communities over time, specific for each individual and for each area of the body. A real "microbial barcode" that identifies us unequivocally, and which can be transferred to everything we come into contact with, including the clothes we wear.
The “contact microbiome”: an indelible signature on clothes
The study conducted by an international team of researchers focused precisely on the transfer of the microbiome from the skin to clothes. The goal was to understand how much of an individual's microbiome is transferred to clothing, how long it persists, and whether some microbes may be more useful than others for identification.
To find out, the researchers had two volunteers wear cotton t-shirts for 24 hours. They then stored the shirts in a controlled environment for six months, along with unworn ones used as controls. At regular intervals, samples of both types of t-shirts were taken, frozen and analyzed to identify the microbial species present.
The results showed that the two volunteers transferred distinct and recognizable microbes onto the shirts, unique to each individual. Furthermore, it was possible to distinguish between worn and unworn items even after a prolonged period. The microbiome remained stable on clothing worn for up to 180 days.
Open questions and prospects for investigation
The study opens fascinating perspectives for forensic investigations, but it also raises new questions. For example, how contaminated can the microbiome be transferred onto clothing from other clothing or the environment? And how much do different tissue surfaces influence the persistence of microbial populations?
Furthermore, we will need to better understand how the microbiome can integrate with other biological traces, such as DNA and body fluids, to strengthen the identifying power of the evidence. And last but not least, it will be crucial to address the ethical and legal implications of the use of the microbiome in investigations, to protect privacy and individual rights.
The discovery that our microbiome leaves an indelible and unique imprint on the clothes we wear, however, can truly revolutionize the way an investigation is conducted. And also open new avenues for medical research, helping us better understand how our microbiome interacts with the environment and influences our health.
