F nucleatum Orange Complex — MFDS Part 1 MCQ

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ModerateMicrobiologyF nucleatum Orange ComplexMFDS Part 1

In the classical Socransky model of subgingival plaque microbial complexes, which species belongs to the orange complex and acts as a coaggregation bridge between early colonisers and late-colonising periodontal pathogens?

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Correct answer: B — Fusobacterium nucleatum

Fusobacterium nucleatum is the correct answer. In the classical Socransky scheme, it belongs to the orange complex. Its broad adhesin-mediated coaggregation enables it to bind early colonisers, including streptococci and Actinomyces species, and later anaerobic periodontal organisms, making it the characteristic bridging species in plaque maturation. Porphyromonas gingivalis is a late coloniser in the red complex. Streptococcus sanguinis is an early coloniser, while Streptococcus mutans is principally associated with cariogenic biofilms rather than this periodontal bridging role. Prevotella intermedia is also an orange-complex organism and is therefore the most plausible distractor, but it is not the canonical bridge linking early and late colonisers.

Reference: Chen Y, Shi T, Li Y, et al. Fusobacterium nucleatum: The Opportunistic Pathogen of Periodontal and Peri-Implant Diseases, Figure 1. Frontiers in Microbiology. 2022. https://pubmed.ncbi.nlm.nih.gov/35369522/