Evaluating the Skin Microbiome ad Trace Evidence

Each of our bodies is covered in billions of bacterial and fungal cells (collectively, microbial cells) that we leave traces of on objects we touch. In previous work, the investigative team has demonstrated that this transfer can associate objects with individual people, and that the microbial signatures are generally stable within a person, raising the potential that these microbial fingerprints could provide important physical evidence. However, several important barriers prevent the use of such evidence. First, we do not know how much contact is required to leave a microbial trace on an object. Second, we do not know whether repeated touches by the same person reinforce or obscure the microbial patterns left behind. Third, we do not know whether an individual’s traces can be resolved from a mixture resulting from multiple people touching the same object. Fourth, we do not know how long an individual’s microbial traces persist on an object. Fifth, we do not know whether the type of surface matters for any of these questions. Finally, we do not know whether we can only match a living person’s skin signature to microbial trace evidence, or, because the microbes in the skin change after death, whether there is a time frame within which we can match evidence between a touched surface and a corpse. If so, we do not know whether or not transportation to, and storage in, the morgue affects the ability to recover that person’s skin microbial signature. We will address these questions in a two-year, five phase research project that brings together the expertise of scientists at the University of California San Diego, University of Colorado, Argonne National Laboratory, Chaminade University of Honolulu, and the City and County of Honolulu Department of the Medical Examiner. We will utilize next-generation DNA sequencing methods to characterize bacterial and fungal communities on the skin and touched objects, a technique that has decreased in cost a millionfold over the past decade, opening it up to routine forensic applications. Together with advanced computational techniques developed in the PI’s lab, these experiments and DNA sequences will provide a robust basis for understanding whether microbial trace evidence has potential for crime scene investigation. The results will be disseminated through academic presentations, workshops, scientific articles, and also through a video aimed at educating both forensic investigators and members of the public about the potential for use of microbial DNA evidence. This project contains a research and/or development component, as defined in applicable law. ca/ncf