Increasing DNA extraction yield from saliva stains with a modified Chelex method

Area of Science:

• Forensic Science
• Molecular Biology
• Genetics

Background:

• Body fluid stain analysis is critical in forensic science.
• DNA typing from stains aids in perpetrator identification and suspect exclusion.
• Efficient DNA extraction from skin-associated stains is challenging.

Purpose of the Study:

• To develop and validate an improved method for genomic DNA extraction from saliva stains on human skin.
• To compare the efficacy of the new method against traditional organic and Chelex extraction techniques.
• To assess the suitability of the extracted DNA for Polymerase Chain Reaction (PCR)-based short tandem repeat (STR) typing.

Main Methods:

• Simulated bite mark scenarios were used to deposit saliva stains on human skin.
• Genomic DNA was extracted using organic (phenol-chloroform) extraction, classical Chelex extraction, and a modified Chelex method.
• The modified Chelex method incorporated pre-extraction with proteinase K and specific temperature incubations (56°C and 100°C) followed by microconcentration.
• DNA quantification was performed to assess recovery rates.

Main Results:

• Classical Chelex extraction yielded a DNA recovery of 31.9 ± 4.22%.
• The modified Chelex extraction method significantly increased DNA recovery to 47.7 ± 6.90%.
• The DNA extracted using the modified method was of sufficient quantity and quality for PCR-based STR typing at two loci.

Conclusions:

• The modified Chelex extraction method offers a substantial improvement in genomic DNA recovery from saliva stains on human skin.
• This enhanced DNA recovery is crucial for increasing the success rate of forensic DNA profiling in challenging casework.
• The developed method provides a more efficient approach for forensic analysis, aiding in accurate identification and exclusion.