The impact of freezing on the post-mortem human microbiome

Abstract

IntroductionHuman donations are often used in forensic research as they can provide unique insights into post-mortem research that cannot be obtained with animal proxies. This is especially true for forensic microbiome research, as human circumstances such as drug-use or health conditions may influence the post-mortem microbiome. However, it is not always feasible to conduct such research immediately after death. Donors are often stored frozen in human taphonomy facilities, pending the start of any experimental study, yet little is known about how freezing may affect their microbiome.MethodsWe assessed the effects of freezing on the post-mortem human microbiome by analysing the microbial diversity and abundance of seven human donors at the Forensic Anthropology Center at Texas State (FACTS) before and after freezing. Swab samples were taken from five locations on each corpse upon arrival to FACTS and again after they had been frozen in storage for a period ranging between 11 and 40 days and subsequently thawed.ResultsAfter performing the microbiome analysis of the swabs via 16S rRNA gene metabarcoding, we found changes in the abundance levels of Proteobacteria, Bacteroidota and Firmicutes, as well as the presence of the new phyla Deinococcota and Myxococcota after freezing. However, none of these changes were significant when comparing community diversity before and after freezing.DiscussionOverall, our results show that the observed changes in the abundance of specific phyla before and after freezing are negligible, that freezing does not significantly alter the human microbiome and that frozen donors are suitable for forensic studies on the human thanatomicrobiome.

Postmortem skin microbiome signatures associated with human cadavers within the first 12 h at the morgue

“…In our investigation, Actinobacteria and Firmicutes slightly decreased over the first 12 h, while Bacteroidetes and Proteobacteria increased. In previous studies Firmicutes was found to be a constant marker between different body areas ( Roy et al, 2021 ), while this phylum and Proteobacteria were found to be the predominant taxa identified from buccal swabs collected from cadavers in different decomposition stages ( Sguazzi et al, 2022 ; Ogbanga et al, 2023 ). The increase in Bacteroidetes is in contrast with previous findings ( Pechal et al, 2018 ), however, the sampling areas must be taken into consideration (face and hands vs. eyes, nose, mouth).…”

From flesh to bones: Multi‐omics approaches in forensic science

“…Two more studies based on an Italian sample composed of oral and skin microbiomes on 50 subjects showed a positive relationship between the abundance of Spirochaetota and Synergistota and the age of the enrolled participants [235,303].…”

“…Pechal et al [234] showed a shift in the post-mortem microbial communities (structure and abundance) during the thawing process of two pediatric cases, whereas Ogbanga et al [235] showed that storing bodies frozen preserves the composition and abundance of their pre-freezing microbiome despite reporting some statistically nonsignificant changes to the post-mortem microbiome post freezing and thawing. These results, despite limited to a few studies, highlight the needs for a better understanding of the effects that storage conditions can have on the bodies, to ensure a correct interpretation of the findings for the identification of potential biomarkers for PMI estimation and human profiling.…”