Inhibition of Streptococcus mutans biofilm accumulation and polysaccharide production by apigenin and tt-farnesol

Objectives: Apigenin is a potent inhibitor of glucosyltransferases and tt-farnesol affects the membrane integrity of Streptococcus mutans. We investigated the influence of apigenin and tt-farnesol, alone and in combination, on the accumulation, polysaccharide composition and viability of S. mutans UA159 biofilms. Methods: Initially, biofilms were grown for 54 h; then, the early-formed biofilms were treated for 1 min twice daily with one of the following: (i) 1.33 mM tt-farnesol; (ii) 1.33 mM apigenin; (iii) apigenin + tt-farnesol (1.33 mM each); (iv) vehicle control (20% ethanol with 0.75% dimethyl sulphoxide); (v) 0.12% chlorhexidine (1.33 mM); or (vi) physiological saline (145 mM NaCl). The procedure was repeated at biofilm ages of 78 and 102 h, and biofilms were harvested at 126 h. The dry weight, protein concentration, number of cfu, and polysaccharide composition per biofilm were determined. Results: The dry weights of the biofilms treated with the test agents were significantly less (30-50%) than those treated with vehicle control (P<0.05). Biofilms treated with the test agents also resulted in lower amounts of extracellular alkali-soluble glucans, intracellular iodophilic polysaccharides and, to a lesser extent, fructans. The fructosyltransferase activity was affected only by apigenin and apigenin + tt-farnesol. The recoverable viable counts of S. mutans were slightly lower (0.5 to 1 log(10) decrease in cfu/biofilm) after apigenin and tt-farnesol treatments compared with the vehicle control. Chlorhexidine displayed potent bactericidal activity, and virtually halted the further accumulation of early-formed (54 h old) biofilms. Conclusions: Apigenin and tt-farnesol affected the accumulation and polysaccharide content of S. mutans biofilms without major impact on the bacterial viability.