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Law Enforcement Investigation Tools Expand Beyond DNA to Bacteria

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By Dena Weiss, Faculty Member, Criminal Justice at American Military University

For the past five years, forensic scientists have been taking advantage of their ability to collect Touch DNA, small samples of DNA from evidence that has been handled by suspects. Items such as vehicle steering wheels, gun grips, door handles, and victims’ clothing have provided valuable evidence linking offenders to a victim or crime scene.

[Related Article: The Crime Scene: Tips for How First Responders Can Help Preserve Key Evidence]

Scientist and microscopeCollection of Touch DNA is simple: Evidence is collected by law enforcement personnel using sterile swabs and submitted to a crime laboratory for analysis. When Touch DNA technology first became available, crime laboratories were limiting evidence processing to violent crimes. As the price of testing procedures decreases, Touch DNA analysis of property crime evidence has become more feasible.

What’s next? New research has found that bacteria may be the next generation of forensic evidence used in police investigations.

What Is a Bacterial Fingerprint?
Even after washing our hands, certain bacteria remain and are often transferred to objects we come in contact with, leaving behind evidence of who has touched what. Research on the life of bacteria resulted in some interesting findings:

  • The average hand contains 150 bacterial species.
  • Women’s hands have approximately 30 percent more species of bacteria than men.
  • Only 13 percent of bacterial species matched between individuals tested.

Research on the Reliability of Bacterial Fingerprints
One of the first research studies on bacterial fingerprints was conducted at the University of Colorado, Boulder and involved swabbing a computer keyboard and mouse of each participant. The bacterial species present were identified by using polymerase chain reaction (PCR) amplification to determine the sequence of gene coding for the 16S ribosomal RNA gene (16S rRNA). The 16S rRNA gene is found in all species of bacteria and is a short strand of DNA that is easily sequenced.

Results of the study showed that it was relatively simple to match each keyboard and mouse sample to the study participant who used the items. Bacterial samples were detected on each computer mouse up to 12 hours after the last touch.

In a similar study conducted by the University of Oregon, cellphones were analyzed for bacteria similarity and dissimilarity. The following results were found:

  • On average, an individual handles a cellphone 150 times a day
  • 7,000 different species of bacteria were found on 51 cellphones
  • 80 percent of the bacteria on an individual’s body is transferred to the cellphone

A total of 17 study participants had their thumb and index fingers swabbed for bacterial content. After swabbing each individual’s cellphone, it was found that 82 percent of the bacteria on the person’s fingers were also present on the cellphone.

Considering how many cellphones are connected to criminal investigations, this could prove to be an excellent investigative tool in the future.

One of the most noteworthy studies conducted in the past year involved the analysis of genital bacteria on hair and was conducted by Murdock University, located in Australia. Samples of human and pubic hair were collected from three males and four females. Only two of the individuals were in a relationship and living together at the time of the study. The hair samples were found to contain bacteria species that were typical for the environment in which each study participant lived, but not unique to that individual. All seven study participants’ pubic hair bacteria profiles were unique.

Of special interest to those conducting the study was the fact that the two people involved in a relationship had similar bacterial content within their pubic hair. It was determined that the couple had engaged in sexual relations 18 hours before the pubic hair samples were collected for the study. This type of biological analysis could prove beneficial in cases of sexual assault where semen is not found.

[Related Article: One Assault, Two Crime Scenes: The Challenge of Handling Sexual Assault Cases]

The use of bacterial fingerprints could prove extremely useful to law enforcement when other pieces of evidence do not exist. It is an area of study that will be continued to be evaluated by forensic scientists and researchers.

Dena Weiss PhotoAbout the Author: Dena Weiss is a full-time professor at American Public University System, teaching courses in criminal justice and forensic science. She has been a crime scene investigator for more than 17 years and is currently a fingerprint expert for a central Florida police department. Prior to that position, she was a serologist for the Florida Department of Law Enforcement. Her court experience includes testifying in court cases in over 15 Florida counties involving more than 200 federal and circuit court cases.

Dena has a bachelor’s degree in chemistry and sociology from Mary Baldwin College and a master’s degree in forensic science from Virginia Commonwealth University. She is currently working on her Ph.D. in business administration with an emphasis in criminal justice.

References:

Briggs, H. (June 24, 2014). Mobile phones carry owners’ bacterial ‘fingerprint’. BBC News Health.

Chawla, D.S. (December 15, 2014). Bacteria on pubic hair could be used to identify rapists. Science.

Cimons, M. (June 7, 2010). Next in forensics: Bacterial ‘fingerprints’. U.S. News & World Report.

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