Could Fusobacterium be a misnomer?

Introduction
Fusobacterium is the genus name of an obligate anaerobic, gram-negative bacilli. Although the name suggests fusiform, we encountered a series of Fusobacterium bacteremia cases with challenging Gram stain appearance.

Methods
The first case was a 74-year-old male admitted to hospital with a fall and failure to thrive. He has a history of gastrointestinal bleed and transcatheter aortic valve implantation for aortic valve stenosis. His anaerobic blood culture bottle later showed gram-negative bacilli with large, round bodies on Gram stain. The second case was a 21-year-old previously healthy female who presented to hospital emergency department with 1 week history of sore throat. Her anaerobic blood culture bottle later showed pleomorphic gram-negative bacilli of varying sizes on Gram stain. The third case was a 56-year-old previously healthy female who was admitted to hospital with a fall and confusion and later required brain craniotomy for evacuation of subdural hematoma. Blood culture was ordered on admission, which later showed no organism on Gram stain despite signaling positive in blood culture monitor. It was then examined by several laboratorians who identified tapered-end gram-negative bacilli discretely showing in the red background of blood culture.

Results
These patients’ blood culture microorganisms were identified using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) mass spectrometry: 1) Fusobacterium mortiferum, 2) Fusobacterium necrophorum, and 3) Fusobacterium nucleatum, respectively.

Conclusions
Species in the Fusobacterium genus have various morphology and clinical implications. Although Fusobacterium necrophorum is classically associated with Lemierre’s syndrome, a life-threatening characterized by septic thrombophlebitis of the internal jugular vein, it is also associated with mild conditions such as pharyngitis, consistent with Case 2 of the current study.