A mixed infection involving Bacteroides denticanum, Lactobacillus salivarius, and Streptococcus anginosus as causative agents of abscess around a pharyngo-esophageal anastomosis and acute vertebral osteomyelitis: Identification by ribosomal RNA sequencing of bacterial isolates.

"Bacteroides denticanum" is an anaerobic, non-spore-forming, gram-negative bacterium with a rod morphology typical of canine, ovine, and macropod oral flora. There is only one report of bloodstream infection caused by "B. denticanum" from a dog bite in human. Here, we report a case with no history of animal contact who developed an abscess caused by "B. denticanum" around a pharyngo-esophageal anastomosis after undergoing balloon dilatation procedure for stenosis following laryngectomy. The patient was a 73-year-old man with laryngeal cancer, esophageal cancer, hyperuricemia, dyslipidemia, and hypertension with a 4-week history of cervical pain, sore throat, and fever. Computed tomography showed fluid collection on the posterior pharyngeal wall. Matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) identified Bacteroides pyogenes, Lactobacillus salivarius, and Streptococcus anginosus from abscess aspiration. 16S ribosomal RNA sequencing re-identified the Bacteroides species as "B. denticanum". T2-weighted magnetic resonance images showed a high signal intensity adjacent to the anterior vertebral body of C3-C7. The diagnosis was peripharyngeal esophageal anastomotic abscess and acute vertebral osteomyelitis caused by "B. denticanum", L. salivarius, and S. anginosus. The patient was treated with sulbactam ampicillin intravenously for 14 days and then switched to oral amoxicillin with clavulanic acid for 6 weeks. To our knowledge, this is the first report of a human infection caused by "B. denticanum" without a history of animal contact. Despite remarkable advancements facilitated by MALDI-TOF MS in microbiological diagnosis, the accurate identification of novel, emerging, or uncommon microorganisms and comprehending their pathogenicity, suitable therapy, and follow up necessitate sophisticated molecular approaches.