Brain abscess can be fatal if not adequately treated. Recent advancements in neurosurgical techniques and culturing methods have allowed for better identification of causative pathogens, and subsequently improved outcome of targeted antibiosis.  In the setting of recent cranial instrumentation, different microbes are more likely culprits than streptococcus and staphylococcus species.

We report the first case in the literature of a brain abscess caused by Bacteroides thetaiotaomicron after recent resection of an invasive cholesteatoma, we also discuss changes in this anaerobe pathogenicity.

A 36-year-old female presented with left otalgia, vertigo, and diminished alertness for two days. She had undergone radical mastoidectomy for invasive cholesteatoma two weeks earlier, and has since received clindamycin, ciprofloxacin-dexamethasone, and methylprednisolone. A gadolinium-enhanced brain MRI visualized a 2.1x2.8 cm enhancing temporal lobe lesion adjacent to the tegmen mastoideum consistent with intraparenchymal abscess with surrounding vasogenic edema. Empiric antibiotics, and dexamethasone were initiated. Stereotactic drainage revealed purulent material whose cultures grew Bacteroides Thetaiotaomicron and Enterococcus avium.

Our case represents the first isolation of Bacteroides Thetaiotaomicron in a brain abscess. There has been one reported case of meningitis with Bacteroides Thetaiotaomicron in the literature. Notably, both cases were associated with cholesteatoma. 

Cholesteatomas create an oxygen-deprived thriving environment for anaerobes to grow and seed into adjacent tissue. Environmental and host factors may favor a diverse gene expression of Bacteroid proteases that could change its behavior, potentially playing a role in exhibiting pathogenicity.

This is important as it drives choice of empiric antibiotic coverage and, given the changes in the pathogenicity of bacteroid species, more aggressive forms of brain infections may be a concern in such settings.