Abstract
Introduction and objectivesIn forensic medicine, the conclusion of death by drowning remains a difficult diagnosis, due to inconstant and aspecific autopsy signs. The detection of aquatic bacteria in blood and organs could support the diagnosis of drowning. The composition of the cadaver microbiome (necrobiome) is still poorly understood, and the same is true of the necrobiome of the drowned cadaver. Our objectives are: i) to study the microbial composition of the cadaver of drowned persons; ii) to identify drowning marker bacteria in fresh and salt water; iii) to develop a detection method that can be used in routine forensic medicine practice.Materials and methodsThirty-six patients autopsied at the Institut Médico-Légal de Montpellier were categorised according to the cause of death and the type of drowning water. DNA from organ and blood samples was extracted and analysed by i) specific PCR targeting zipA (Aeromonas spp.) and pyrH (Vibrio spp.) (189 samples); ii) metabarcoding on the rrs V3-V4 portion by Illumina mi-seq sequencing, swarm clustering, phylo-taxonomic affiliation (Silva) and calculation of alpha and beta diversity indices (12 samples). Results, discussion and conclusionThe metabarcoding approach carried out on 2 patients, one drowned in freshwater and the other in the sea, shows a necrobiome that varies between patients and between organs. The necrobiome of the drowned patient was composed of bacteria from the human microbiome and aquatic bacteria (Aeromonadaceae and Vibrionaceae). The diversity of the necrobiome differs quantitatively and qualitatively between patients and therefore according to the type of drowning water. The lungs of patients drowned in fresh water showed very different necrobiomes from those of other organs.Detection of Aeromonas and Vibrio by PCR supported the diagnosis of drowning in 14/32 drowning victims. Aeromonas is particularly associated with freshwater drowning, but the distribution of the 2 genera according to the type of water is not strict. The results suggest that metabarcoding should be carried out on other drowning patients and on drowning water. A good knowledge of aquatic bacteria and their dynamics in necrobiomes would make it possible to target taxa for more accessible specific PCR approaches in a forensic context.