In vitro study of possible microbial indicators for drowning: Salinity and types of bacterioplankton proliferating in blood

Numbers and types of bacterioplankton proliferating in blood samples mixed with water of various salinity levels were examined to determine the characteristics of species associated with salinity. Water samples (total n = 88) were collected from the midstream of two rivers (freshwater; n = 10; salinity <0.05%), from around their estuaries (areas of freshwater, n = 20, salinity <0.05%; areas of brackish water, n = 20, salinity <0.05-3.1%; areas of marine water beyond the mouths of the rivers, n = 28, salinity 2.4-3.3%), and from the coast (areas of marine water; n = 10; salinity 3.3-3.5%). Freshwater bacteria were identified in 41 of 42 blood samples mixed with water at ≤1.3% salinity, and the genus Aeromonas, which is universally distributed in freshwater environments, was predominant. Marine bacteria were identified in all of 46 blood samples mixed with water at ≥1.8% salinity, and most comprised the genera Vibrio and Photobacterium that are universally distributed in seawater environments. Aeromonas was undetectable in all blood samples mixed with brackish or sea water at ≥1.8% salinity although they are detectable even in seawater environments. Thus, the present results showed that bacterioplankton capable of proliferating in human blood reflects the salinity of water.