Using oral microbial DNA analysis to identify expirated bloodspatter

Area of Science:

• Forensic Science
• Microbiology
• Molecular Biology

Background:

• Distinguishing expirated bloodstains from impact spatter is a forensic challenge.
• Oral streptococci are specific to human saliva, offering a potential marker.

Purpose of the Study:

• To develop a sensitive and specific polymerase chain reaction (PCR) method for detecting oral bacteria in bloodstains.
• To assess the utility of this PCR method in forensic analysis of expirated bloodstains.

Main Methods:

• Developed a PCR assay targeting DNA from human oral streptococci.
• Tested specificity against human DNA and other microbes.
• Assessed sensitivity, inhibition by blood, and stability in bloodstains on various materials over time.
• Validated the method in a blind trial using mock forensic samples.

Main Results:

• The PCR method demonstrated high specificity for oral streptococci, with no cross-reactivity to human DNA or other tested microbes.
• Sensitivity was as low as 60 fg of target DNA, with 99% success on saliva samples.
• PCR was not inhibited by blood and detected DNA in expirated bloodstains for up to 92 days on cardboard and cotton.
• The method correctly distinguished expirated bloodstains from others in a blind trial.

Conclusions:

• Oral bacteria DNA can be reliably detected in bloodstains using the developed PCR method.
• This bacterial marker shows promise for distinguishing mouth-expirated bloodstains in forensic casework.
• The PCR assay offers a sensitive, specific, and robust tool for forensic bloodstain analysis.