Products from bacteria play multiple functions in biofilm formation

Objective: The oral microbial flora consists of many species of bacteria that are associated with the healthy condition and control the progression of dental diseases e.g. dental caries and periodontal disease. Cooperative interactions between oral streptococci, Actinomyces naeslundii and various pathogens play important roles in the development of dental biofilms in the oral cavity. To determine the roles of oral bacteria in multi-species biofilm development and the effects of active substances {exo-beta-D-fructosidase (FruA) and short fatty acids}, which are produced from oral bacteria in cell growth and metabolism, were tested in the biofilm formation of Streptococcus mutans GS-5 and A. naeslundii x600. Methods: Commercial FruA and various short futty acids were applied in the bacterial solution on saliva-coated 96-well microtiter plate and hydroxyapatite disk in Tryptic soy broth without dextrose supplemented with 0.25% sucrose for 16 hours incubation at 37°C. After washing with PBS, the biofilm was stained by 0.25% safranin and measured by absorbance at 492 nm. Results: FruA inhibited completely the biofilm formation of S. mutans GS5 on polystylene and hydroxyapatite surfaces in dose-dependent manner. The inhibiting effects were dependent on the sucrose concentration in medium. The inhibition was induced by decreasing production of polysaccharide dependent on sucrose digestion rather than fructan digestion. In contrast, 6.25 mM butyric acid, 3.125 mM valeric acid and 12.5 mM acetic acid in short futty acids elevated the biofilm formation of A. naeslundii. The elevation was induced by increasing production of polysaccharide dependent on stress proteins, and membrane-damaged cells. Conclusion: These data indicate various products from oral bacteria play multiple functions in the limited condition and FruA or short fatty acid may play an important role in multi-species microbial interactions for sucrose-dependent biofilm formation in the oral cavity.