Detection of bacterioplankton in immersed cadavers using selective agar plates

We measured bacterioplankton in blood from cadavers retrieved from the sea (n = 12), near estuaries (n = 4), rivers (fresh water, n = 8) and from bathtubs (n = 4) as well as from non-drowned victims (n = 10) discovered near aquatic environments. Blood from 11 victims drowned in seawater developed bioluminescent and/or blue colonies (oxidase test positive) on selective media containing 2-4% NaCl. Homology analyses of the 16S rRNA gene showed that all of them were marine bacteria (genera: Photobacterium, Vibrio, Shewanella, Psychrobacter). Blood from all victims drowned in rivers generated blue colonies on plates containing ≤3%, but not 4% NaCl. Homology analyses showed that the blue colonies were generated from bacteria that inhabit fresh water (Aeromonas). None of the blood samples from victims that drowned in bathtubs generated bioluminescent and blue colonies. However, all cadavers contained bacteria that produced unstained colonies (Staphylococcus, Bacillus, Enterobacter, Escherichia, etc.). Among non-drowned victims, blood from two gave rise to blue colonies on plates containing ≤3% NaCl (Pseudomonas). Of the cadavers found near estuaries, bioluminescent and blue colonies developed from two of them on media containing 2-4% NaCl (Photobacterium, Vibrio, Listonella), but not from two others on plates containing 4% NaCl (at ≤3%; blue colonies, Aeromonas; unstained colonies, Citrobacter, Vagococcus, Proteus, Enterobacter). These results suggested that the presence of numerous bacterioplankton in immersed cadavers could support a conclusion of death by drowning.