## 3 Results and Discussion
### Antimicrobial Activity  
With regard to the growth kinetics of _Streptococcus mutans_ in S\({}_{\mathrm{A}}\) and X\({}_{\mathrm{A}}\), growth was not observed in the latter extract (Figure 1). A similar result was obtained with the negative control (chlorhexidine). Some studies state that the contents of flavonoids, tannins, and condensed phenols of high molecular weight in dragon's blood rhizomes are responsible for the antimicrobial properties found within the extracts [9; 53]. Other research suggests that the antimicrobial activity of dragon's blood rhizome extracts is due to the presence of terpen such as \(\beta\)-sitosterol and citalititone [11]. The synergy among these compounds could play an important role in the antimicrobial properties found in the extracts. The results observed for the negative control (chlorhexidine) are mainly due to its cationic nature, which allows its adherence to the bacterial cell wall; at low concentrations, it increases permeability, filtrating intracellular components (bacterostatic effect), while at high concentrations, it precipitates the bacterial cytoplasm and causes cell death (bactericidal effect) [2]. Exponential growth of _S. mutans_ was observed after 20 h in the adaptation phase (Lag) in the positive control; the growth rate at the logarithmic phase was \(\mu\) = 0.487 h\({}^{-1}\) (r\({}^{2}\)= 0.976) (Figures 1 and 2). The non-sterilized xoconostle fruit extract (5 mg/mL) only delayed _S. mutans_ growth until 4 h, compared to the positive control during the adaptation phase (Lag); the growth rate at the logarithmic phase was \(\mu\) = 0.588 h\({}^{-1}\) (r\({}^{2}\) = 0.970). The antimicrobial properties of xoconostle extracts were reported by [PERSON] and [PERSON] [6]; however, the concentration at which xoconostle fruit extracts reported activities similar to the negative control (chlorhexidine) ranged between 28 and 80 mg/mL, which is relatively high compared to the antiseptic compounds that are contained in commercial mouth  
Figure 1: Growth kinetics of _Streptococcus mutans_ in unsterilized extracts: (\(\blacklozenge\)) dragon’s blood rhizomes (5 mg/mL); (\(\blacksquare\)) xoconostle (5 mg/mL); (\(\blacktriangle\)) negative control (chlorhexidine); (\(\blacksquare\)) positive control; SA: unsterilized dragon’s blood rhizome extract, X\(\mathrm{A}\): unsterilized xoconostle fruit extract; CN: control negative; CP: control positive. rinses, considering that the concentrations of the active compounds in these commercial products range between 1 and 2 mg/mL [54]. The growth kinetics of _S. mutans_ in \(\mathrm{S_{B}}\) and \(\mathrm{X_{B}}\) are shown in Figure 2. \(\mathrm{S_{B}}\) and \(\mathrm{S_{A}}\) extracts presented similar behaviors; the growth values (log CFU/mL) did not vary, and thus, the temperature during the sterilization treatment did not affect the antimicrobial activity in the dragon's blood rhizome extracts. On the other hand, the growth was delayed by 12 h in the \(\mathrm{X_{B}}\) extracts when compared with the \(\mathrm{X_{A}}\) extracts during the adaptation phase (Lag), while the growth rate at the logarithmic phase in the \(\mathrm{X_{B}}\) extracts was \(\mu\) = 0.289 h\({}^{-1}\) (r\({}^{2}\) = 0.991). Therefore, the antimicrobial properties of the non-sterilized and autoclave-sterilized extracts of dragon's blood plant rhizomes did not change their behavior; meanwhile, the extracts of autoclave-sterilized xoconostle fruit delayed the appearance of the logarithmic phase and decreasing growth rate values (\(\mu\)); however, they did not show antimicrobial activity at a concentration of 5 mg/mL. After comparisons of growth kinetics between non-sterilized and autoclave-sterilized extracts were performed, we decided to determine the MIC exclusively for the autoclave sterilized extracts (the antioxidant properties did not vary, the antimicrobial activity against _S. mutans_ was maintained, and native microbiota were deleted from the extracts).