Initial insights into bacterial succession during human decomposition

Abstract

Decomposition is a dynamic ecological process dependent upon many factors such as environment, climate, and bacterial, insect, and vertebrate activity in addition to intrinsic properties inherent to individual cadavers. Although largely attributed to microbial metabolism, very little is known about the bacterial basis of human decomposition. To assess the change in bacterial community structure through time, bacterial samples were collected from several sites across two cadavers placed outdoors to decompose and analyzed through 454 pyrosequencing and analysis of variable regions 3-5 of the bacterial 16S ribosomal RNA (16S rRNA) gene. Each cadaver was characterized by a change in bacterial community structure for all sites sampled as time, and decomposition, progressed. Bacteria community structure is variable at placement and before purge for all body sites. At bloat and purge and until tissues began to dehydrate or were removed, bacteria associated with flies, such as Ignatzschineria and Wohlfahrtimonas, were common. After dehydration and skeletonization, bacteria associated with soil, such as Acinetobacter, were common at most body sites sampled. However, more cadavers sampled through multiple seasons are necessary to assess major trends in bacterial succession.

Soil fungal community shift evaluation as a potential cadaver decomposition indicator

“…37]. As a consequence, the need for comprehensive databases for bacterial populations characteristic of decomposing cadavers and gravesoils were highlighted [5,37]. Our study illustrates the requirement for a similarly rigorous impetus to understand fungal community dynamics in gravesoils, including the use of accessible ecogenomics techniques in protracted further work.…”

Postmortem succession of gut microbial communities in deceased human subjects

“…While other studies of postmortem human microbial communities have included fecal or rectal sampling (e.g., Hyde et al, 2015; Hyde et al, 2013), here we provide an examination of communities in the proximal large intestine (caecum). The bacterial communities in these decomposing individuals had a distinct compositional shift in the middle of the bloat phase of decomposition, between days four and seven in this study.…”

“…There has been recent interest in the use of microbial communities in the decomposition environment as markers of PMI: if the postmortem succession of microbial communities is repeatable and predictable, then it may be possible to use the communities as forensic indicators, similar to the approach taken by forensic entomology (Amendt, Krettek & Zehner, 2004). Recent studies have begun describing human postmortem microbial communities associated with a variety of habitats, including skin (Metcalf et al, 2016; Pechal et al, 2017; Hyde et al, 2015), mouth and rectum (Hyde et al, 2015; Hyde et al, 2013), ear and nasal canals (Johnson et al, 2016), internal organs (Javan et al, 2016; Tuomisto et al, 2013), bones (Damann, Williams & Layton, 2015) and soils below (Metcalf et al, 2016; Cobaugh, Schaeffer & DeBruyn, 2015). Other studies have also reported postmortem changes associated with decomposing animal carcasses (Pechal et al, 2013a; Metcalf et al, 2013; Heimesaat et al, 2012; Burcham et al, 2016; Dickson et al, 2011).…”

Microbial effects on the development of forensically important blow fly species

“…As decomposition continues, the microbial community changes as bacteria move from sites internal to the body to locations on the surface, and are transferred from the soil, scavengers and insects [15,17,23]. Different species of bacteria are known to be associated with different stages of the decomposition process.…”

“…During the bloat stage, Ignatzschineria and Wohlfahrtimonas bacteria are commonly found on the skin of the corpse, and anaerobic bacteria including Lactobacillus and Bacteriodes increase in the abdominal 3 cavity [18]. Microbial communities on a corpse generally become less diverse [23,25] and more similar to each other across body sites [15] with time.…”