In the world of microbiology, the microbial communities we harbor in and on us (our microbiomes) are considered increasingly interesting. In Boulder, Colorado, the dedicated detectives who investigate these complex communities are members of an elite squad known as the forensic microbiologists. These are their stories.
Jessica Metcalf has giant hair—self-confessed. When talking about the skin microbes we all shed just by moving through our daily lives, she jokes that some of us may spread more than others: “those of us with giant hair”.
Jessica was speaking about the perils of hair flipping at the Front Range Computational & Systems Biology Symposium last Tuesday, where scientists gathered at Colorado State University to talk about microbiomes, pathogen detection, and infection tracking. She spoke specifically about applications of microbiome research in crime-solving.
Like the infamous Pig-Pen from the Charlie Brown comics, we constantly jettison our skin microbes into the air and onto the surfaces we touch. This gives our surroundings a flavor of the microbial communities present on the skin of everyone who passes through. While in Rob Knight’s lab at CU Boulder, Jessica helped to show that individuals can be identified by these communities because each person has a slightly different set of bacteria living with them.
By having a roomful of volunteers touch a variety of surfaces (glass, plastic, ceramic, etc.), Jessica found that some materials are better or worse tattle-talers. Ceramic, for example, makes it easy for scientists to determine who touched it—glass, not so much. The researchers know it’s partly due to the abrasiveness of the surface (more scraping, more evidence), but are continuing to investigate what properties of the material have the biggest impact on whether scientists can identify a person.
These findings have intriguing implications for crime scene analysis. Could forensic scientists use the bacterial signature left behind to narrow down the list of culprits? Researchers in Florida recently tested this by staging a burglary, and then swabbing surfaces of the burgled house. They found that they could reliably determine who broke in. Of course this method is error prone, and there will still be a large burden of proof beyond microbiome similarity. However, it does suggest a future with two separate methods of “fingerprinting”: we might start swabbing for microbial fingerprints before dusting for human fingerprints.
Jessica ended on a slightly grislier application of microbiome research: decomposition analysis. When bodies decay, the microbes living with them change in predictable ways. As illustrated gruesomely (and luckily not after lunch) with the progressing decomposition of a pig, microbial communities change as the niche changes. In this case, the niche is changing as decay progresses.
Unperturbed by the gory subject matter, Jessica explained how useful it can be to study the changing microbial communities over the course of decomposition. Theoretically, we could be able to estimate time of death (or at least day of death) given the microbial makeup of remains. This method, along with insect colonization and other indicators, could help forensic scientists more accurately guess when somebody died.
Jessica recently accepted a position at CSU, where she will continue to spread her skin microbes via hair toss, as well as study forensic microbiology.
By Alison Gilchrist