Dental caries is one of the most common
infectious diseases that affects humans. Streptococcus mutans, the main pathogenic bacterium associated with
dental caries, produces a number of extracellular
sucrose-metabolizing
enzymes, such as
glucosyltransferases (GTFB, GTFC and
GTFD) and
fructosyltransferase (FTF). The cooperative action of these
enzymes is essential for
sucrose-dependent cellular adhesion and biofilm formation. A global response regulator (vicR) plays important roles in S. mutans ftf and gtf expression in response to a variety of stimuli. A real-time reverse-transcription polymerase chain-reaction was used to quantify the relative levels of ftf, gtfB, gtfC,
gtfD and vicR transcription of S. mutans in the presence of various
dietary carbohydrates:
sucrose,
D-glucose, D-
fructose,
D-glucitol (D-
sorbitol),
D-mannitol and
xylitol. Ftf was highly expressed at late exponential phase in the presence of
sorbitol and
mannitol. GtfB was highly expressed in the presence of all the above
carbohydrates except for
xylitol at early exponential growth phase and
glucose and
fructose at late exponential growth phase. Similar to gtfB, the expression of gtfC was also induced with the presence of all the tested
carbohydrates except for
xylitol at early growth and
glucose and
fructose at late exponential phase. In addition, no effect of
mannitol on gtfC expression at early exponential phase was observed.
GtfD was less influenced compared to the gtfB and gtfC, demonstrating enhanced expression especially in the presence of
sorbitol,
glucose,
mannitol and
xylitol at early exponential phase and
mannitol at late exponential phase. VicR expression was induced only at the presence of
xylitol at late exponential phase, and a decrease in expression was recorded at early exponential phase. Our findings show that
dietary carbohydrates have a major influence on the transcription of ftf, gtfB, gtfC and
gtfD, but less on vicR.
Sorbitol and
mannitol, which are considered as noncariogenic
sugar substitutes, may indirectly affect caries by promoting biofilm formation via enhanced expression of gtfs and ftf. These results suggest regulatory circuits for exopolysaccharide gene expression in S. mutans.