Abstract
The human microbiome has begun to emerge as a potential forensic tool,
with varied applications ranging from unique identification to
investigative leads that link individuals and/or locations. The relative
abundance of the combined DNA of the microbiome, compared to human
nuclear DNA, may expand potential sources of biological evidence,
especially in cases with transfer or low-copy number DNA samples. This
work sought to determine the optimal swab type for the collection and
analysis of the microbiome. A bacterium (Proteus mirabilis) was
deposited by pipette onto four swab types (cotton, flocked, dental
applicators, and dissolvable), and extraction and real-time PCR
quantitation of the bacterial DNA were performed, which allowed for
absolute microbial DNA recovery and comparison of yields across the four
sampling substrates. Flocked swabs had the highest yield
(~1240 ng) compared to the cotton swabs
(~184 ng), dental applicators (~533 ng),
and dissolvable swabs (~430 ng). The collection
efficiency was further evaluated for cotton and flocked swabs using
dried microbial samples spotted onto non-porous surfaces (treated wood,
glass, plastic, and tile). Flocked swabs performed consistently better
across wood, glass, and tile, but showed decreased recovery from
plastic. The cotton swabs failed in the recovery of P. mirabilis DNA
across all surfaces. Knowing the appropriate sampling substrate will be
useful as others continue to investigate the use of the microbiome as a
forensics tool.