Research of diatoms and aquatic bacteria for estimating drowned site of a decomposed cadaver

在涨潮和退潮时，我们在两条河流河口附近的不同地点采集了68个淡水、咸淡水和海水样本。海水在河口上游约2.4（盐度2.2%）和1.2公里（1.8%）处流动，但表面基本上由淡水组成，一直到河口。每50毫升水中含有69 - 22200个硅藻，数量因深度而异，相隔仅约1.2公里的地点也不同。硅藻的大小为2.8 ~ 429 μm（平均16.1 ~ 59.2）。大型pennate硅藻分布在淡水地区，大多数在到达海洋之前就沉积了。潮汐和河流的性质经常改变同一河口地点的硅藻组合。建议对含水介质进行法医解释以推断溺水地点时要谨慎。我们还在两具浸泡在河口环境中的尸体的血液样本中检测到许多生物发光细菌。基于16S rRNA基因的同源分析表明，这两种发光菌落分别为费氏弧菌（Vibrio fischeri）和哈维弧菌（V. harveyi），它们通常生活在海水中。这些在浸泡在水中的尸体的血液中的发现表明是咸淡水或海水吸入，因为我们之前的研究表明，很少有其他海洋细菌侵入并在死后占主导地位。这种简单而快速的细菌学测试有可能作为支持溺水死亡结论的标记。

We collected 68 fresh, brackish and sea water samples from various sites around the estuaries of two rivers at high and low tides. Sea water flowed about 2.4 (salinity, 2.2% at the site) and 1.2 km (1.8%) upstream of the estuaries, but the surface comprised essentially fresh water up to the mouth. Sites contained 69 - 22,200 diatoms/50 ml of water and the numbers varied by depth and at sites separated by only about 1.2 km. Diatoms ranged from 2.8 to 429 (mean range, 16.1-59.2)μm in size. Large pennate diatoms populated fresh water areas, and most sedimented before reaching the sea. Tides and the nature of the river often altered diatomaceous assemblages at the same estuarial sites. Caution is recommended for forensic interpretation of aqueous media to deduce drowning sites.We also detected numerous bioluminescent bacteria in blood samples from two cadavers that had been immersed in estuarine environments. Homologous analysis based on the 16S rRNA gene identified the bioluminescent colonies as Vibrio fischeri and V. harveyi, which normally inhabit seawater. These findings in the blood from immersed bodies suggested brackish or marine water aspiration because our previous study showed that few other marine bacteria invade and predominate post mortem. This simple and rapid bacteriological test has potential as a marker supporting a conclusion of death by drowning.