New study shows DNA in bacteria key to identifying sexual offenders

December 18, 2014

New research will assist forensic investigations into sexual crimesGround-breaking research by a team of Australian scientists may assist forensic investigations into sexual crimes where no DNA evidence is left behind by the offender.

The study, led by Murdoch University PhD researcher Ms Silvana Tridico in partnership with a team of expert scientists has identified unique bacterial signatures, found to differ from person to person through microbial DNA.

“Studies on the human microbiome (the collective genomes present in the human body) suggest that there are significant differences in bacterial composition not only between different body sites but also between individuals,” Ms Tridico said.

“This study is the first to suggest cross-transference of pubic and/or genital bacteria as a result of intercourse and although further analyses needs to be conducted, this initial finding bodes well for future forensic applications involving sexual crimes.”

Previous research around the transfer of pubic hairs in forensic investigations involving sexual assault cases discovered limited transfer (four per cent) of male pubic hair to the female genital area during sexual intercourse.

“In most cases, the majority of hairs recovered in forensic investigations are shed hairs that have ceased to grow and contain little or no nuclear DNA. What is special about this process is that it would not involve extra or additional extraction procedures, as DNA isolation procedures for human DNA will also ‘collect’ microbial DNA,” Ms Tridico said.

Bacterial communities, associated with human scalp and pubic hair were surveyed using a multiplex barcoded sequencing approach from seven healthy Caucasian individuals of both sexes (two of whom were in a de facto relationship), ranging in age from 23 and 53 years old.

Scalp and pubic hair samples were collected at the start of the study and at two and five month intervals thereafter. Researchers carried out an analysis of the hair samples to identify microbial DNA in order to build a picture of the microbial communities that were present.

Ms Tridico, forensic scientist and mammalian hair analysis expert found that male pubic hairs could be readily distinguished from female pubic hairs on the basis of their respective microbiota. It was also found that all individuals harboured unique bacteria on their pubic hairs, in addition to personalised bacteria that formed part of the normal skin flora.

“Lactobacillus was the most prevalent bacteria that clearly differentiated male and female pubic hair microbiota,” Ms Tridico said.

“While the microbial communities on pubic hair generally remained individually distinct and consistent over the course of the study, in one instance at the five month time point, the co-habiting couple’s microbiota were more similar to each other than previously.

“Interviewing revealed that the couple had sexual intercourse 18 hours prior to the collection of their pubic hairs this clearly suggests that an exchange of microbes had occurred.

“This is an encouraging result, and a positive step forward for future forensic investigations involving sexual crimes.”

Ms Tridico hopes to secure funding to continue her research in this area, with the belief that it could one-day become a standard part of the forensic investigation toolkit identifying offenders of sexual assault crimes where DNA evidence is lacking.

“Further funding will help us maintain the current momentum in moving this research forward, and the potential of this study to provide evidence where currently there is none can only strengthen and augment forensic capabilities,” she said.

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