MALDI-TOF Mass Spectrometry Analysis and Human Post-Mortem Microbial Community: A Pilot Study

Abstract

Introduction: The human post-mortem microbiome (HPM) plays a major role in the decomposition process. Successional changes in post-mortem bacterial communities have been recently demonstrated using high throughput metagenomic sequencing techniques, showing great potential as a post-mortem interval (PMI) predictor. The aim of this study is to verify the application of the mass spectrometry technique, better known as MALDI-TOF MS (matrix-assisted laser desorption/ionization time-of-flight mass spectrometry), as a cheap and quick method for microbe taxonomic identification and for studying the PM microbiome. Methods: The study was carried out on 18 human bodies, ranging from 4 months to 82 years old and with a PMI range from 24 h up to 15 days. The storage time interval in the coolers was included in the final PMI estimates. Using the PMI, the sample study was divided into three main groups: seven cases with a PMI < 72 h; six cases with a PMI of 72–168 h and five cases with a PMI > 168 h. For each body, microbiological swabs were sampled from five external anatomical sites (eyes, ears, nose, mouth, and rectum) and four internal organs (brain, spleen, liver, and heart). Results: The HPM became increasingly different from the starting communities over time in the internal organs as well as at skin sites; the HPM microbiome was mostly dominated by Firmicutes and Proteobacteria phyla; and a PM microbial turnover existed during decomposition, evolving with the PMI. Conclusions: MALDI-TOF is a promising method for PMI estimation, given its sample handling, good reproducibility, and high speed and throughput. Although several intrinsic and extrinsic factors can affect the structure of the HPM, MALDI-TOF can detect the overall microbial community turnover of most prevalent phyla during decomposition. Limitations are mainly related to its sensitivity due to the culture-dependent method and bias in the identification of new isolates.

The Future Is Now: Unraveling the Expanding Potential of Human (Necro)Microbiome in Forensic Investigations

“…Different studies showed an increase in bacterial richness and a decrease in diversity from the early to late decomposition stages (Table 1) [9,70]. These studies have also consistently demonstrated an increase in Pseudomonadota and a decrease in Actinomycetota and Bacteroidota, with particular relevance in the rectum [71,72]. Additionally, another study has reported a negative linear relationship between the overall phylum and family taxa with PMI.…”

“…Other approaches involving transcriptomics and proteomics, which provide functional community information and/or a global snapshot of the physiological and biochemical state of a sample, can be highly valuable (e.g., when DNA is absent or degraded as in hair or bone samples) and are increasingly explored [152,153]. Also, flow cytometry (evaluating DNA degradation) and MALDITOF-MS (Matrix-assisted laser desorption/ionization timeof-flight mass spectrometry) or MALDI-IMS (Matrix-assisted laser desorption/ionization imaging mass spectrometry), respectively able to accurately identify bacteria at the species level and profiling the proteins and peptides in tissue sections, have been explored as promising tools for PMI calculation [71,154,155].…”

Forensic Microbiology: When, Where and How

“…The most abundant taxa of microbial communities according to the organ examined are Firmicutes in the brain, heart and spleen [12,24,30]; Firmicutes and Proteobacteria in the liver [12,13,30]; Bacteroidetes, Firmicutes and Pro-teobacteria in the oral cavity [31]; Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes and Proteobacteria in the bones [32]. According to another study, the predominant phyla in the post-mortem microbiota are Firmicutes and Proteobacteria [33].…”