Application of DNA repair for Streptococcus salivarius DNA-based identification of saliva from ultraviolet-exposed samples

Abstract

Forensic samples are commonly influenced by various environmental factors, including ultraviolet (UV) irradiation; thus, forensic applications of DNA repair (e.g., PreCR™, Restorase®) have been investigated, focusing on short tandem repeat typing. However, current DNA-based examinations are used for both human and body fluid identification. This study thus aims to clarify the efficacy of a DNA repair approach for Streptococcus salivarius DNA-based identification of saliva from UV-damaged samples. Artificial UV-damaged genomic DNA of S. salivarius, drop saliva stains, and buccal swabs were used to evaluate the effects of DNA repair on S. salivarius DNA detection by using PreCR™ repair reagent. To evaluate forensic applications, we prepared mock forensic samples by exposing them to environmental conditions. Melting curve analysis following real-time PCR was applied for qualitatively detecting S. salivarius DNA with a specific melting peak of 80.5°C±0.4°C (n=10, mean ± 3SD). Single PCR was used for quantitative and qualitative analyses, whereas dual PCR was used for S. salivarius DNA qualitative detection. DNA repair experiments using artificial UV-damaged samples revealed a significant increase of only the quantitative value of genomic DNA samples by DNA repair. Moreover, significant quantitative DNA repair effects were not observed in all mock forensic samples, indicating the limitations of DNA repair for actual cell-derived DNA samples. Whereas, differences of qualitative results (with or without detection) were generated for mock forensic samples; thus, we consider the DNA repair strategy as an additional approach for S. salivarius DNA-based identification of saliva from environmentally damaged evidence.