PCR detection of bacterial genes provides evidence of death by drowning

We have developed a sensitive and specific PCR method for detecting plankton DNA in cases of death by drowning. However, this PCR method could not be used for cases of drowning in water containing no plankton. Bacteria species are normally localized in the throat and trachea and they may invade into blood through the respiratory tract in people who have drowned as well as species localized in water. The aim of this study was to establish a novel and expedient PCR method for detecting bacterial genes in samples from drowning cases. We designed primer pairs for Streptococcus salivarius (SL1) and Streptococcus sanguinis (SN1), which are common species in the throat, and for Aeromonas hydrophila (AH1), which has been found in various water samples. With SL1, SN1, and AH1, we detected 10, 0.1, and 1 pg of target DNA, respectively. Among 19 drowned cases within 3 days postmortem, SL-DNA was detected in all of the blood samples from hearts with SL1 and AH-DNA was detected in several samples with AH1. In a case of drowning in a bathtub, use of the conventional acid digestion method for diatom analyses and the PCR method for identifying plankton DNA revealed no plankton, but our PCR method for detecting bacterial DNA showed a positive result for SL-DNA in a blood sample from the heart. In conclusion, our novel PCR method is highly specific and sensitive for detecting bacterial DNA and is useful for cases of death by drowning in water containing no plankton.