Identify the Fusobacterium species considered the most frequent isolate recovered from clinical infections.

• A. Fusobacterium nucleatum
• B. Fusobacterium varium
• C. Fusobacterium mortiferum
• D. Fusobacterium necrophorum

Answer: (A)

Fusobacterium nucleatum is the most frequently recovered Fusobacterium species in clinical infections because it is a common member of the normal oral microbiota and plays a key role in bridging and promoting polymicrobial infections. In the mouth, it readily coaggregates with a wide range of bacteria, helping establish and expand biofilms. This ability to interact with many partners makes it a frequent resident in infections that originate in the oral cavity or spread from it, such as dental abscesses, periodontal disease-related infections, and various mixed anaerobic infections in the head, neck, abdomen, and pelvis. Its prevalence in diverse anaerobic infections explains why it is the species most often isolated in clinical specimens.

Other Fusobacterium species are associated with more specific contexts. For example, Fusobacterium necrophorum is well known for causing oropharyngeal infections that can lead to Lemierre syndrome, but it does not occur as commonly as a general isolator across a wide range of clinical infections. Fusobacterium mortiferum and Fusobacterium varium are less frequently recovered overall and are more limited to particular niches or infection scenarios, rather than being the predominant isolates in routine clinical specimens.