A child with recurrent otitis media due to Bacteroides thetaiotaomicron.

Brain abscess remains a life-threatening condition. Here, we are reporting a case of brain abscess due to Bacteroides thetaiotaomicron in a previously known case of recurrent otitis media. A 15 years old boy with a history of recurrent otitis media presented with the complaints of right otalgia, headache and fever. Computed Tomography (CT) brain and neck revealed fluid filled right middle ear cavity with bony destruction along the inner cortex of right temporal bone. The abscess was drained and culture showed growth of Bacteroides thetaiotaomicron. This report illustrates the importance of MALDI-TOF MS in the species level identification of anaerobes thereby facilitating the selection of appropriate and prompt adjuvant antibiotic therapy. This timely identification thus led to a favourable outcome in an era of increasing antimicrobial resistance.

A surface endogalactanase in Bacteroides thetaiotaomicron confers keystone status for arabinogalactan degradation.

Glycans are major nutrients for the human gut microbiota (HGM). Arabinogalactan proteins (AGPs) comprise a heterogenous group of plant glycans in which a ß1,3-galactan backbone and ß1,6-galactan side chains are conserved. Diversity is provided by the variable nature of the sugars that decorate the galactans. The mechanisms by which nutritionally relevant AGPs are degraded in the HGM are poorly understood. Here we explore how the HGM organism Bacteroides thetaiotaomicron metabolizes AGPs. We propose a sequential degradative model in which exo-acting glycoside hydrolase (GH) family 43 ß1,3-galactanases release the side chains. These oligosaccharide side chains are depolymerized by the synergistic action of exo-acting enzymes in which catalytic interactions are dependent on whether degradation is initiated by a lyase or GH. We identified two GHs that establish two previously undiscovered GH families. The crystal structures of the exo-ß1,3-galactanases identified a key specificity determinant and departure from the canonical catalytic apparatus of GH43 enzymes. Growth studies of Bacteroidetes spp. on complex AGP revealed 3 keystone organisms that facilitated utilization of the glycan by 17 recipient bacteria, which included B. thetaiotaomicron. A surface endo-ß1,3-galactanase, when engineered into B. thetaiotaomicron, enabled the bacterium to utilize complex AGPs and act as a keystone organism.