Objective: To establish a method for amplifying specific 16S rDNA fragment of algae related with drowning and test its value in drowning diagnosis.
Methods: Thirty-five rabbits were randomly divided into 3 the drowning group (n=15), postmortem water immersion group (n=15, subjected to air embolism before seawater immersion), and control group(n=5, with air embolism only). Twenty samples of the liver tissues from human corpses found in water were also used, including 14 diatom-positive and 6 diatom-negative samples identified by microwave digestion-vacuum filtration-automated scanning electron microscopy (MD-VF-Auto SEM). Seven known species of algae served as the control algae (Melosira sp, Nitzschia sp, Synedra sp, Navicula sp, Microcystis sp, Cyclotella meneghiniana, and Chlorella sp). The total DNA was extracted from the tissues and algae to amplify the specific fragment of algae followed by 8% polyacrylamide gelelectrophoresis and sliver-staining.
Results: In the drowning group, algae was detected in the lungs (100%), liver (86%), and kidney (86%); algae was detected in the lungs in 2 rabbits in the postmortem group (13%) and none in the control group. The positivity rates of algae were significantly higher in the drowning group than in the postmortem group (P<0.05). Of the 20 tissue samples from human corps found in water, 15 were found positive for algae, including sample that had been identified as diatom-negative by MD-VF-Auto SEM. All the 7 control algae samples yielded positive results in PCR.
Conclusions: The PCR-based method has a high sensitivity in algae detection for drowning diagnosis and allows simultaneous detection of multiple algae species related with drowning.