The bacteria in biofilm responsible for 'bridging' between early and late colonizers is:

Correct answer: B. Fusobacterium nucleatum

• A. Actinomyces is an early colonizer that attaches to the acquired pellicle — it does not serve the bridging function between early and late colonizers.
• B. FUSOBACTERIUM NUCLEATUM is the classic 'bridge' organism in dental biofilm/plaque. It is a mid-colonizer that co-aggregates with BOTH early colonizers (Streptococcus, Actinomyces) AND late colonizers (P. gingivalis, T. forsythia, T. denticola). Without Fusobacterium bridging, the Red Complex periodontopathic bacteria cannot effectively integrate into the biofilm. It is the 'central hub' of the plaque succession model.
• C. S. mutans is an EARLY colonizer associated with caries — not the bridge organism in periodontal biofilm.
• D. P. gingivalis is a LATE colonizer (Red Complex) that arrives AFTER Fusobacterium has already bridged the transition — it relies on F. nucleatum to integrate.