Impact of Various Fusobacterium Species on In Vitro Biofilm Formation

Objectives: Fusobacteria are common obligately anaerobic Gram-negative bacteria of the oral cavity that may act as a bridge between early and late colonizing bacteria in dental plaque. Previous experiments had shown that growing biofilms without F. nucleatum resulted in a significant decrease of total CFU in the Zürich supragingival biofilm-model. The aim of this study was to investigate the impact of various Fusobacterium species on in vitro biofilm formation and structure.
Methods: The standard six-species supragingival biofilm employed contained Actinomyces oris, Candida albicans, Streptococcus mutans, Streptococcus oralis, Veillonella dispar, and Fusobacterium sp. Six different Fusobacterium species or subspecies, respectively, were tested namely F. nucleatum ssp. fusiforme, F. nucleatum ssp. nucleatum, F. nucleatum ssp. polymorphum, F. nucleatum ssp. vincentii, F. naviforme, and F. periodonticum). Biofilms were grown anaerobically on hydroxyapatite discs in 24-well culture dishes. After 64 h biofilms were either harvested and quantified by culture analysis or proceeded to fluorescent in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM).
Results: All Fusobacterium species established well in the biofilms. Their CFU ranged from 1.4E+04 (F. nucleatum ssp. fusiforme) to 5.6E+06 (F. nucleatum ssp. nucleatum). Despite this relatively broad range in CFU, none of the Fusobacterium species had a significant effect on total CFU nor on CFUs of the single species except for F. nucleatum ssp. polymorphum, which significantly decreased the CFU of V. dispar (p<0.01).
Conclusions: This study showed that incorporation of various Fusobacterium species did not affect overall growth of the biofilm suggesting that probably all tested Fusobacterium species are able to act as a bridge between their surrounding partners. The growing capacities of the different fusobacteria within the biofilms may also vary, depending on the particular species.