Effects of Extended Postmortem Interval on Microbial Communities in Organs of the Human Cadaver.

Holly Lutz,Jack A Gilbert,Sheree J Finley,Silvia Visona,Gulnaz T Javan,Neil Gottel,Alexandria Vangelatos,Antonio Osculati

doi:10.3389/fmicb.2020.569630

Abstract

Human thanatomicrobiota studies have shown that microorganisms inhabit and proliferate externally and internally throughout the body and are the primary mediators of putrefaction after death. Yet little is known about the source and diversity of the thanatomicrobiome or the underlying factors leading to delayed decomposition exhibited by reproductive organs. The use of the V4 hypervariable region of bacterial 16S rRNA gene sequences for taxonomic classification (“barcoding”) and phylogenetic analyses of human postmortem microbiota has recently emerged as a possible tool in forensic microbiology. The goal of this study was to apply a 16S rRNA barcoding approach to investigate variation among different organs, as well as the extent to which microbial associations among different body organs in human cadavers can be used to predict forensically important determinations, such as cause and time of death. We assessed microbiota of organ tissues including brain, heart, liver, spleen, prostate, and uterus collected at autopsy from criminal casework of 40 Italian cadavers with times of death ranging from 24 to 432 h. Both the uterus and prostate had a significantly higher alpha diversity compared to other anatomical sites, and exhibited a significantly different microbial community composition from non-reproductive organs, which we found to be dominated by the bacterial orders MLE1-12, Saprospirales, and Burkholderiales. In contrast, reproductive organs were dominated by Clostridiales, Lactobacillales, and showed a marked decrease in relative abundance of MLE1-12. These results provide insight into the observation that the uterus and prostate are the last internal organs to decay during human decomposition. We conclude that distinct community profiles of reproductive versus non-reproductive organs may help guide the application of forensic microbiology tools to investigations of human cadavers.

Highlights

During life, the human microbiome serves important health-related functions including nutrient acquisition, pathogen defense, energy salvage, and immune defense training (Gilbert et al, 2016)
Sampling spanned postmortem interval (PMI) of 24–432 h [avg (SD) = 111 (± 93) h] and included tissues from cadavers corresponding to different causes of death grouped into four categories according to each internal organ: accidental (n = 51), natural (n = 63), homicide (n = 13), and suicide (n = 31) (Table 1)
We identify a number of cadaver-specific traits to be associated with microbial alpha and beta diversity, as well as bacterial taxa that are differentially associated with these traits

Summary

Introduction

The human microbiome serves important health-related functions including nutrient acquisition, pathogen defense, energy salvage, and immune defense training (Gilbert et al, 2016). Postmortem microbial communities’ succession related to human remains has been proven to be predictable and applicable for forensic science and criminal investigations (Damann et al, 2015; DeBruyn and Hauther, 2017; Pechal et al, 2018). Recent studies have shown that the microbiome may be used to estimate the amount of time that has elapsed since death, referred to as the postmortem interval (PMI), allowing investigators to establish a potential timeline of death (Maujean et al, 2013; Pechal et al, 2014; Cobaugh et al, 2015; Hauther et al, 2015; Burcham et al, 2016; Javan et al, 2016; Metcalf et al, 2016; Javan et al, 2017)

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