Which organism is described as bridging species in oral biofilms?

• A. Streptococcus mutans
• B. Fusobacterium nucleatum
• C. Veillonella
• D. Porphyromonas gingivalis

Answer: (C)

Bridging species in oral biofilms are organisms that link early colonizers with later, more anaerobic members, helping the biofilm mature through both attachment networks and metabolic interactions. Veillonella fits this role because early colonizers like Streptococcus churn out lactate as they metabolize sugars. Veillonella uses that lactate as its carbon source, so it thrives where lactate is plentiful. By consuming lactate, Veillonella reduces local acid buildup and creates conditions more favorable for other anaerobic bacteria that follow in the biofilm’s progression. At the same time, Veillonella can adhere to early colonizers and to later-arriving species, effectively acting as a physical and metabolic bridge that connects the initial surface-attached community to the deeper, more diverse microbial network. This combination of metabolic cross-feeding and coaggregation explains its bridging role in oral biofilms.