Abstract

Bacteria into dental biofilm are subjected to dietary episodes of ‘feast and famine’ conditions that should be simulated when models of biofilm are developed because the expression of genes related to sucrose metabolism may change. Thus, the aim was to evaluate the effect of sucrose exposure constantly (‘feast’) or intermittently (‘fast’) on expression of glucosyltransferases and dextranases of S. mutans growing in a biofilm. S. mutans UA159 biofilms were formed on saliva-coated bovine enamel slabs in batch culture and they were grown in ultrafiltered tryptone-yeast extract broth at 37°C, 10% CO2 during 5 days. The biofilms (n = 4) were exposed to 1% sucrose constantly or 10% sucrose 8x/day and after 105 h of growth they were collected for analysis. The RNA was extracted from biofilms with acid phenol/chloroform, purified and the expression of gtfB, gtfC, gtfD and dexA genes were evaluated by quantitative PCR. The results were normalized related to 16S gene content and also expressed relative to the expression of control group, in which biofilms were grown in culture medium without sucrose exposure. The results showed that dexA gene expression of biofilm exposed to sucrose 8x/day was higher than sucrose exposure constantly (p < 0.05) but the expressions of gtfB, gtfC and gtfD did not differ (p> 0.05). The findings suggest that the condition of intermittent sugar exposure that occurs daily in the oral cavity should be simulated in vitro when models of biofilm are used to evaluate sucrose metabolism.