Influence of swabbing solution and swab type on DNA recovery from rigid environmental surfaces

Determination of the metagenome has become an important component of forensic identification, which requires efficient environmental sampling techniques. Therefore, in this study, we compared the efficiency of sample collection using swabbing with cotton swabs and three types of medical swabs (S7, S22, S24) along with three different solutions: phosphate-buffered saline (PBS), 1% Tween 20 + 1% glycerol in PBS (TG), and GS commercial solution (Noble Bio, Hwaseong, Republic of Korea). Combinations of the three solutions with the three types of swabs were tested at different volumes (cotton swab, S7: 0, 30, 50, 70 μL; S22, S24: 0, 70, 100, 130 μL). Escherichia coli and Staphylococcus aureus were selected as representative environmental microbial samples, and the number of colony-forming units (CFUs), DNA concentration, and DNA copy numbers were compared across groups. The sampling process had a clear effect on the efficiency of extraction, which allowed for determination of a more efficient sample sampling method. In particular, cotton swabs showed 2-10-fold greater CFUs of both species than the medical swabs, and resulted in significantly greater amounts of extracted DNA. TG was found to be the most efficient solution for bacterial DNA extraction, with higher CFUs and DNA obtained than with the other three solutions at all volumes tested. This study highlights the need for a standardized sampling method that can be applied to all environmental samples, especially for microbial quantification, and provides valuable reference data for the efficient collection of environmental samples for metagenomic analyses in microbial-based forensic assessments.