Assessment of viable bacteria and bacterial DNA in blood and bloodstain specimens stored under various conditions

Microbial forensic specimens that are collected at biocrime and bioterrorism scenes include blood, tissue, cloths containing biological fluids, swabs, water, soil, and aerosols. It is preferable that pathogens in such specimens are alive and kept in a steady state. Specimens may be stored for a prolonged period before analysis; therefore, it is important to understand the effect of the storage conditions on the pathogens contained within the specimens. In this study, we prepared blood and bloodstain specimens containing Gram-negative or -positive bacteria, stored the samples for 482 days under various conditions, and measured viable bacterial counts and total bacterial contents in the samples. Viable bacteria were preserved well in the samples stored at −30 and −80 °C, but were diminished or undetectable in the samples stored at 4 °C and room temperature. The total bacterial content was maintained in the blood samples stored at −30 and −80 °C and in the bloodstain samples stored under all temperature conditions, but decreased in the blood samples stored at 4 °C and room temperature. This study showed that the storage conditions affected viable bacteria and bacterial DNA and that freezing and drying were significant for their long-term storage. We provide important information for the storage of microbial forensic specimens.