Dental biofilm composition and gtf expression in response to carbohydrates

Streptococcus mutans biofilm formed under starch with sucrose combination presents distinct composition of extracellular polysaccharide (EPS) and gtf genes expression than those formed in response to the isolated exposure to these carbohydrates.Objective: Since there is limited knowledge about this phenomenon in vivo, Methods: a crossover and blind study was conducted in four steps of 14 days each. During each step 11 volunteers wore palatal appliance containing 10 slabs of dentine to which the following treatments were applied extraorally: 2% starch gel-like solution (starch group); 10% sucrose solution (sucrose group); a solution containing 2% starch and 10% sucrose (starch+sucrose group), or 2% starch solution followed by 10% sucrose solution (starch®sucrose group). On the 14th day of each phase the biofilms were collected for biochemical and microbiological analyses. Results: The results (Avg±SD; n=11) according to the treatments were, respectively: Soluble EPS (µg/mg wet weight) = 1.2±1.0, 7.6±4.8, 5.5± 4.7 and 4.8± 6.8; Insoluble EPS (µg/mg wet weight) = 0.9±0.9, 15.8±12.0, 16.2±15.5 and 12.0±12.5. For all the response variables, the treatment with starch differed statistically from the others (p<0.001) but these did not differ between them (p>0.05). The same trend was observed for mutans streptococci and lactobacilli counts in dental biofilm, but neither treatment differed statistically with regard to actinomyces (p>0.05). Furthermore, RNA were successfully isolated and purified from in situ biofilms and only biofilms formed in response to sucrose and starch sucrose combinations showed detectable levels of gtfB and gtfC mRNA. Conclusions: The findings suggest that the biofilms formed in situ in response to starch or sucrose are distinct with regard to their EPS composition and gtf genes expression but the changes provoked by starch/sucrose combinations were not different than those observed for sucrose alone.

Supported by FAPESP (Procs. 04/00688-3; 05/04703-0) and CNPq 305680/2007-2)