Fluorescently labeled bacteria provide insight on post-mortem microbial transmigration

Abstract

Microbially mediated mechanisms of human decomposition begin immediately after death, and are a driving force for the conversion of a once living organism to a resource of energy and nutrients. Little is known about post-mortem microbiology in cadavers, particularly the community structure of microflora residing within the cadaver and the dynamics of these communities during decomposition. Recent work suggests these bacterial communities undergo taxa turnover and shifts in community composition throughout the post-mortem interval. In this paper we describe how the microbiome of a living host changes and transmigrates within the body after death thus linking the microbiome of a living individual to post-mortem microbiome changes. These differences in the human post-mortem from the ante-mortem microbiome have demonstrated promise as evidence in death investigations. We investigated the post-mortem structure and function dynamics of Staphylococcus aureus and Clostridium perfringens after intranasal inoculation in the animal model Mus musculus L. (mouse) to identify how transmigration of bacterial species can potentially aid in post-mortem interval estimations. S. aureus was tracked using in vivo and in vitro imaging to determine colonization routes associated with different physiological events of host decomposition, while C. perfringens was tracked using culture-based techniques. Samples were collected at discrete time intervals associated with various physiological events and host decomposition beginning at 1h and ending at 60 days post-mortem. Results suggest that S. aureus reaches its highest concentration at 5-7 days post-mortem then begins to rapidly decrease and is undetectable by culture on day 30. The ability to track these organisms as they move in to once considered sterile space may be useful for sampling during autopsy to aid in determining post-mortem interval range estimations, cause of death, and origins associated with the geographic location of human remains during death investigations.

Postmortem succession of gut microbial communities in deceased human subjects

“…Another Clostridiales, Anaerosphaera spp., have been previously isolated from animal waste reactors and identified as aminolytic anaerobes, fermenting amino acids into volatile fatty acids (Ueki et al, 2009), implicating them as members of the putrefactive consortia as well. Mouse model studies examining translocation of bacteria postmortem have demonstrated the migration and proliferation of Clostridium and other anaerobic taxa in the internal organs with increasing postmortem intervals (Heimesaat et al, 2012; Burcham et al, 2016); an increase in Clostridium in human internal organs postmortem has also been reported (Javan et al, 2016; Tuomisto et al, 2013). Clostridia are known putrefactive organisms, so their observed increase in relative abundance may be due to an increase in vegetative growth, where they gained energy through the fermentation of cellular products.…”

“…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). Collectively these studies are beginning to reveal general patterns of microbial succession, which include a shift towards a higher relative abundance of anaerobic taxa.…”

Abiotic and Biotic Factors Regulating Inter-Kingdom Engagement between Insects and Microbe Activity on Vertebrate Remains

“…Almost immediately following host death, microbially-mediated decomposition begins, and commensal microbes begin to translocate following the cessation of host immune function, facilitated by the upregulation of genes for motility and production of exoenzymes for utility in breaking down tissues for nutrient availability [93]. Depending upon the placement of the cadaver, non-indigenous microorganisms, particularly soil microbial communities, may also “invade” the cadaver.…”

“…Depending upon the placement of the cadaver, non-indigenous microorganisms, particularly soil microbial communities, may also “invade” the cadaver. As the local environment moves from aerobic to anaerobic, proliferation of anaerobic commensal microbes takes place, leading to the process of putrefaction, where carbohydrates, lipids, and proteins are bound and fermented, releasing gases [93,94,95]. In this same sense, insect colonization will also impact resource quality for the microbe.…”

Nesting strategies and disease risk in necrophagous beetles

“…Topsoil microorganisms near to the carcass use these nutrients for growth (Yang, ), increasing their activity, and the same might be expected of potentially opportunistic microbes and insect pathogens. Although general effects of carrion decomposition on microorganisms have indeed been shown, most of these studies have had a forensic focus (Burcham et al., ; Cobaugh et al., ; Finley, Pechal, Benbow, Robertson, & Javan, ; Guo et al., ; Hopkins, Wiltshire, & Turner, ; Howard, Duos, & Watson‐Horzelski, ; Olakanye, Thompson, & Komang Ralebitso‐Senior, ; Pechal et al., ). Considering the facts above, it is clear that insects that exploit carcasses are exposed to an abundant and highly active microbial community (Figure ).…”