Methods: The S. mutans GS-5 ftf gene was expressed in E. coli SG13009, using the pQE30 expression vector. The recombinant FTF was purified using a Ni-NTA resin (Qiagen). Affinity of several strains of oral bacteria to immobilized FTF was conducted by applying the surface plasmon resonance (SPR) technique using Biacore 3000 (Pharmacia Biosensor). The recombinant FTF was immobilized on the sensorchip (CM5) and binding of bacteria was determined over a range of concentrations 2X106-3X109 CFU/ml. The SPR signal obtained in each reaction cycle was recorded as a sensorgram, which presented a real-time reaction of the FTF with the adhered bacteria. The sensorgram was plotted as resonance units (RU), versus time (seconds).
Results: Streptococcus mutans, Streptococcus sobrinus and Actinomyces viscosus showed significant affinity to FTF. A. viscosus had highest association rate (ka) with FTF, ka=1.86x10-7 CFU-1s-1, while the ka for S. mutans and for S. sobrinus was 1.10x10-7 CFU-1s-1 and 1.03x10-7 CFU-1s-1 respectively. However, the affinity constant (KA) of S. mutans to FTF was 1.5 times higher than S. sobrinus, and 3 times higher than A. viscosus.
Conclusion: The present results suggest that the immobilized FTF can act as binding sites for oral bacteria and may influence bacterial adherence and colonization of the dental biofilm. Our study demonstrates that biomolecular interaction analysis using SPR can be suitable for in vitro adhesion characterization of oral bacteria to constituents of the acquired pellicle.