Abstract
BackgroundPostmortem microbiological examinations are performed in forensic and medical pathology for defining uncertain causes of deaths and for screening of deceased tissue donors. Interpretation of bacteriological data, however, is hampered by false-positive results due to agonal spread of microorganisms, postmortem bacterial translocation, and environmental contamination.Methodology/Principal FindingsWe performed a kinetic survey of naturally occurring postmortem gut flora changes in the small and large intestines of conventional and gnotobiotic mice associated with a human microbiota (hfa) applying cultural and molecular methods. Sacrificed mice were kept under ambient conditions for up to 72 hours postmortem. Intestinal microbiota changes were most pronounced in the ileal lumen where enterobacteria and enterococci increased by 3–5 orders of magnitude in conventional and hfa mice. Interestingly, comparable intestinal overgrowth was shown in acute and chronic intestinal inflammation in mice and men. In hfa mice, ileal overgrowth with enterococci and enterobacteria started 3 and 24 hours postmortem, respectively. Strikingly, intestinal bacteria translocated to extra-intestinal compartments such as mesenteric lymphnodes, spleen, liver, kidney, and cardiac blood as early as 5 min after death. Furthermore, intestinal tissue destruction was characterized by increased numbers of apoptotic cells and neutrophils within 3 hours postmortem, whereas counts of proliferative cells as well as T- and B-lymphocytes and regulatory T-cells decreased between 3 and 12 hours postmortem.Conclusions/SignificanceWe conclude that kinetics of ileal overgrowth with enterobacteria and enterococci in hfa mice can be used as an indicator for compromized intestinal functionality and for more precisely defining the time point of death under defined ambient conditions. The rapid translocation of intestinal bacteria starting within a few minutes after death will help to distinguish between relevant bacteria and secondary contaminants thus providing important informations for routine applications and future studies in applied microbiology, forensic pathology, and criminal medicine.
Highlights
Bacterial infections cause death in humans at all ages
Given that acute and chronic intestinal inflammation is accompanied by distinct gut microbiota changes, but only little is known about gut flora shifts in vertebrate animals after death under defined conditions, we performed a kinetic survey of postmortem (p.m.) changes in the main bacterial groups within the colon lumen by culture after mice harboring a conventional microbiota had been sacrificed by cervical dislocation and stored at constant ambient conditions for up to 3 days
Given that cultural methods are tidiuos, time-consuming and require special expertise for detection and subcultivation of fastidious species such as obligate anaerobic bacteria when performing a detailed survey of the complex intestinal microbiota, we applied molecular methods which assessed replicating bacteria and the entire bacterial ‘‘genetic mass’’, including bacteria having died in the meantime, contributing to a more complete picture of the complex microbiota
Summary
Bacterial infections cause death in humans at all ages. A correct interpretation of results derived from appropriate specimens by pathologists is essential to draw the conclusion of a causal relationship between the detected pathogenic microorganism and the fatal outcome. Whenever a clear medical history is unavailable and autopsy or histological results are unspecific, postmortem microbiological examinations are essential tools. Postmortem microbiological examinations are performed in forensic and medical pathology for defining uncertain causes of deaths and for screening of deceased tissue donors. Interpretation of bacteriological data, is hampered by false-positive results due to agonal spread of microorganisms, postmortem bacterial translocation, and environmental contamination
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