Extracellular polysaccharides (EPS) are the major components of microbial biofilms and they play a keyrole in the formation of dental caries. The effect of antimicrobial agents on EPS structures remains unknown, and considering this lack of information, this was the aim of the present study.Streptococcus mutans UA159 biofilms were grown for 5 days on glass slides and were treated 2x/day with chlorhexidine digluconate (CHX) at 0.12% (concentration with recognized anti-biofilm effect), formulation with and whithout Baccharis dracunculifolia (a native plant from Brazil, presenting potential anticariogenic effect), or 0.9% NaCl (negative control).On the 6th day the biofilms were collected and the bacterial viability was determined. An insoluble EPSwas extracted from the biofilms and analyzed by nuclear magnetic resonance spectroscopy. EPS´s structural differences were compared by Principal Component Analysis (PCA).Only CHX was able to decrease bacterial viability (p < 0.05). Structural analysis showed that EPS from all biofilms are α-glucans containing different proportions of(1→6)- and (1→3)-linkages. Regarding PCA analysis,the first principal component described 86.4% of the variance and showed that biofilm formed in the presence of formulation without B. dracunculifolia was similar to negative control while CHX and formulation with B. dracunculifolia presented distinct profile. The main chemical shifts contributing to differentiation were 3.69, 3.88, 3.53 and 3.48 ppm. Therefore, the results suggested that CHX decreased the bacterial viability and modified the chemical structure of EPS formed in its presence, as well.In contrast, the presence of B. dracunculifoliadid not show an antibacterial effect, although the produced EPS have also presented a modified chemical structure, which was evidenced by PCA analysis. Analysis by PCA of EPSfrom biofilms formed in presence of different treatments allowed their structural determination and highlighted the power of employing this technique in order to study future design of antibiofilm therapies.
