PCR-based detection of salivary bacteria as a marker of expirated blood

Distinguishing between bloodstains caused by a spatter pattern or by expirated blood may be crucial to a forensic investigation. Expirated blood is likely to be contaminated with saliva but current techniques have limited sensitivity, especially with small bloodstains. We report that a PCR assay, designed to detect salivary bacteria, can amplify streptococcal DNA from saliva stains applied to fabrics for at least 62 days after seeding. Bacterial DNA was detected when 0.01 µl of saliva was present in the stain and the amplification was not affected by contamination with blood. These findings indicate that PCR amplification of salivary microbial DNA may have application in the identification of expirated bloodstains in forensic case-work.