# Odontogenic Brain Abscess in a Hereditary Haemorrhagic Telangiectasia (HHT) Patient: Case Report with a Comprehensive Literature Review

## TL;DR

A rare case of a brain abscess caused by multiple oral bacteria is reported, highlighting new microbial species and the importance of advanced diagnostic techniques.

## Contribution

First report of Ca. Saccharibacteria oral taxon 488 in a clinical sample and in a brain abscess.

## Key findings

- Twelve anaerobic bacterial species were detected in the brain abscess, including previously unreported ones.
- The obligate epibiotic lifestyle of Ca. Saccharibacteria oral taxon 488 was confirmed through co-detection with Arachnia propionica.
- Next-generation sequencing proved valuable for identifying fastidious or uncultivable organisms in polymicrobial infections.

## Abstract

Background: Recent diagnostic methods have enabled the detection of often culture-negative pathogens, including anaerobic bacteria from the oral cavity. Characterising the microbial diversity and co-occurrence of bacteria in such infections is important for understanding the molecular pathophysiology in odontogenic brain abscesses. Case presentation: We describe a case of polymicrobial odontogenic brain abscess in a 59-year-old man of Vietnamese ethnicity with a documented increased risk of brain abscess due to Hereditary Haemorrhagic Telangiectasia (HHT). The microbiological diagnostic work-up included conventional culture, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), targeted 16S rDNA analysis using three broad-range group-specific PCR (polymerase chain reaction) assays and next-generation sequencing (NGS). A literature review was conducted, including database searches for each identified microorganism. Twelve anaerobic bacterial species were detected, among which Treponema medium, Capnocytophaga HMT-323 and Candidatus Saccharibacteria oral taxon 488 have not previously been reported in brain abscesses. In addition, we identified the extremely rare pathogens Arachnia propionica and Capnocytophaga ochracea. Conclusion: This is the first report of Ca. Saccharibacteria oral taxon 488 in a clinical sample and the first detection of any species from this phylum in a brain abscess, co-detected with A. propionica, consistent with its obligate epibiotic lifestyle. Our findings broaden the known microbial diversity associated with odontogenic brain abscesses and underscore the value of 16S rDNA NGS in characterising polymicrobial infections, particularly when fastidious or uncultivable organisms are involved.