Evaluation of four digestive methods for extracting diatoms.
OBJECTIVE
To compare the merit of four digestive methods (nitric acid plus hydrogen peroxide, proteinase K, nitric acid in Disorganization Can and Soluene-350) for extracting diatoms in order to choose the best digestive method for the diagnosis of drowning.


METHODS
Liver, kidney and bone marrow of rabbits were minced and then digested by four digestive methods separately with the following indices compared: (1) time demanded for complete digestion; (2) degree of digestion for different tissues; (3) the reclaiming ratio of diatoms; (4) the degree of digestive destruction to diatoms.


RESULTS
For sufficiently digesting the same tissue, the demanded times for the different methods ranked from the longest to the shortest were as follows: Soluene-350, proteinase K, nitric acid plus hydrogen peroxide, nitric acid in Disorganization Can. Nitric acid in Disorganization Can method and nitric acid plus hydrogen peroxide method digested the tissues more thoroughly than proteinase K, than Soluene-350 methods. For Cyclotella and Cybella, proteinase K method reclaimed most diatoms and nitric acid plus hydrogen peroxide method reclaimed less, while nitric acid in Disorganization Can and Soluene-350 methods reclaimed the least. For Navicula, the majority of diatoms could be extracted using proteinase K method, but only a few diatoms with other three methods. Under scanning electron microscopy (SEM), the structure of diatoms remained almost perfect after digestion with proteinase K, but destroyed to some extent with other three methods.


CONCLUSIONS
This study demonstrated that different diatoms (in fresh or sea water) have different resistance to different digestive reagents. As far as the reliability and applicability of the diatom test is concerned, proteinase K method is of the best choice, nitric acid plus hydrogen peroxide can be its substitute. Soluene-350 cannot be used for extracting sea water diatoms.
Ming
Mei
M
Department of Forensic Medicine, Medical College, Wuhan University, Donghu Road 115, Wuhan 430071, PR China. stillwatermm@hotmail.com
Meng
Xiangzhi
X
Wang
Enyin
E
D000818:Animals; D001853:Bone Marrow / Q000382:microbiology*; D017377:Diatoms / Q000302:isolation & purification*; D004332:Drowning / Q000382:microbiology; D019286:Endopeptidase K; D005260:Female; D049429:Forensic Pathology; D006861:Hydrogen Peroxide; D007202:Indicators and Reagents; D007668:Kidney / Q000382:microbiology*; D008099:Liver / Q000382:microbiology*; D008297:Male; D017942:Nitric Acid; D000644:Quaternary Ammonium Compounds; D011817:Rabbits
D007202:Indicators and Reagents; D000644:Quaternary Ammonium Compounds; C002982:Soluene; D017942:Nitric Acid; D006861:Hydrogen Peroxide; D019286:Endopeptidase K