A simple DNA coprecipitation method for the detection of diatoms in heart blood

We developed a method for detecting and enumerating diatoms in the heart blood of drowning victims and evaluate its utility for diagnosing death by drowning. For purification of diatoms from blood, the DNA binding ability of the diatom frustule in the presence of a chaotropic agent was utilized. The procedure is basically the same as the commonly used method for DNA purification from blood using Proteinase K treatment and denaturation by a chaotropic agent. DNA adsorbed to the diatom (DNA/diatom complex) is recovered by ethanol precipitation, and the DNA is subsequently digested using DNase. Purified diatoms could be clearly observed under a microscope. Diatoms spiked in the blood of non-drowned cadavers (n = 15) were well recovered, and were detected in heart blood from all drowning victims (n = 22). The mean number of diatoms found in 5 ml of blood from drowning victims was 7.8 ± 5.8 (mean ± SD), and the number of diatoms detected in the blood of the left ventricle (6.1 ± 5.8) was approximately two times higher than that of the right ventricle (3.0 ± 2.7, p < 0.05). These results suggest that this simple and safe method can become an effective tool for diagnosing the cause of death as drowning.