Characterising Post-mortem Bacterial Translocation Under Clinical Conditions Using 16S rRNA Gene Sequencing in Two Animal Models

Identification of bacterial pathogens in sudden unexpected death in infancy and childhood using 16S rRNA gene sequencing

Background

Sudden unexpected death in infancy (SUDI) is the most common cause of post-neonatal death in the developed world. Following an extensive investigation, the cause of ~40% of deaths remains unknown. It is hypothesized that a proportion of deaths are due to an infection that remains undetected due to limitations in routine techniques. This study aimed to apply 16S rRNA gene sequencing to post-mortem (PM) tissues collected from cases of SUDI, as well as those from the childhood equivalent (collectively known as sudden unexpected death in infancy and childhood or SUDIC), to investigate whether this molecular approach could help identify potential infection-causing bacteria to enhance the diagnosis of infection.

Methods

In this study, 16S rRNA gene sequencing was applied to de-identified frozen post-mortem (PM) tissues from the diagnostic archive of Great Ormond Street Hospital. The cases were grouped depending on the cause of death: (i) explained non-infectious, (ii) infectious, and (iii) unknown.

Results and conclusions

In the cases of known bacterial infection, the likely causative pathogen was identified in 3/5 cases using bacterial culture at PM compared to 5/5 cases using 16S rRNA gene sequencing. Where a bacterial infection was identified at routine investigation, the same organism was identified by 16S rRNA gene sequencing. Using these findings, we defined criteria based on sequencing reads and alpha diversity to identify PM tissues with likely infection. Using these criteria, 4/20 (20%) cases of unexplained SUDIC were identified which may be due to bacterial infection that was previously undetected. This study demonstrates the potential feasibility and effectiveness of 16S rRNA gene sequencing in PM tissue investigation to improve the diagnosis of infection, potentially reducing the number of unexplained deaths and improving the understanding of the mechanisms involved.

Bacterial Invasion of Pulp Blood Vessels in Teeth with Symptomatic Irreversible Pulpitis

INTRODUCTION

This study described the degenerative changes and infection patterns of the pulp tissue associated with symptomatic irreversible pulpitis.

METHODS

The material consisted of 32 extracted teeth with untreated deep caries that were clinically and histologically diagnosed with irreversible pulpitis and were part of the histopathologic collection of 1 of the authors. The controls consisted of intact teeth with normal uninflamed pulps and teeth with reversible pulpitis. Teeth were processed for histopathologic and histobacteriologic analyses.

RESULTS

All teeth with irreversible pulpitis showed areas of severe acute inflammation, necrosis, microabscesses, and bacterial infection in the pulp chamber. These areas were surrounded by a chronic inflammatory infiltrate, and, at the distance, the pulp tissue was often uninflamed. Bacteria were also observed in the areas surrounding the necrotic foci, both as scattered cells through the extravascular space and at varying numbers within the blood vessel lumen. The number of bacteria and the density of the intravascular bacterial aggregations varied considerably. In one third of the cases, bacteria occurred in the lumen of venules in areas at a considerable distance from the necrotic focus in the coronal third of the root. No intravascular bacteria were noted in the middle and apical segments of the canal. No bacteria were found in the pulps of any of the control specimens.

CONCLUSIONS

Bacterial invasion and colonization of necrotic areas were observed in the pulp of all teeth with caries exposure and symptomatic irreversible pulpitis. Bacterial penetration of blood vessels occurred in all cases, suggesting that this may be an important mechanism of spread of bacterial infection through the pulp tissue in an endodontic infection.