Which Fusobacterium species is most frequently isolated from clinical infections?

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

Answer: (B)

Among Fusobacterium species, nucleatum is the most frequently isolated from clinical infections. Its prominence comes from being a major component of the oral microbiota and its ability to participate in many polymicrobial infections by acting as a bridging organism that coaggregates with a wide range of other bacteria. This leads to it being recovered in diverse infection sites, including head and neck, intra-abdominal, and bacteremic specimens. While necrophorum is a clinically important pathogen—especially in oropharyngeal infections that can lead to Lemierre's syndrome—its overall frequency of isolation is lower than that of nucleatum. The other two species are detected much less often in routine clinical infections.