## 3 Results and Discussion
### Antimicrobial Activity  
Sage and pennyroyal HSs did not exert high enough antimicrobial activity against the tested oral pathogens so neither MIC nor MBC/MFC could be determined. However, oregano HS exerted antibacterial activity against both tested pathogens. MIC was determined at 25% \(\circ\)/\(v\) and 35% \(v\)/\(v\) for _S. mutans_ and _C. albicans_, respectively. MFC value was equal to MIC for _C. albicans_, whereas MBC was determined at slightly higher value of 30% \(v\)/\(v\) for _S. mutans_ (Table 3). On the contrary, all tested EOs demonstrated antimicrobial activity against both pathogens, ranging from 0.05% \(v\)/\(v\) to 0.45% \(v\)/\(v\) regarding MIC for _S. mutans_, and 0.05% \(v\)/\(v\) to 0.4% \(v\)/\(v\) regarding MIC for _C. albicans_. Similarly, MBC/MFC values were determined, ranging from 0.05% \(v\)/\(v\) to 0.45% \(v\)/\(v\) for _S. mutans_, and from 0.05% \(v\)/\(v\) to >0.5% \(v\)/\(v\) for _C. albicans_ (Table 3). Apparently, oregan essential oil exerted the strongest antimicrobial activity against both tested pathogens. Sage EO demonstrated the second highest antibacterial activity against _S. mutans_ (MIC 0.25% \(v\)/\(v\) and MBC at 0.35% \(v\)/\(v\)), whereas pennyroyal EO was the second most active against _C. albicans_ (both MIC and MFC determined at 0.25% \(v\)/\(v\)). The most abundant active substance carvacrol, present in oregano EO was tested as control for comparison. Both MIC and MBC were determined at 0.0315% \(v\)/\(v\), corresponding to roughly 63% of carvacrol measured by GC-MS in oregano EO. Similarly, carvacrol MIC and MFC against _C. albicans_ was determined at 0.0175% \(v\)/\(v\) and 0.0315% \(v\)/\(v\), respectively. The quest to develop novel antimicrobial agents against resistant microorganisms is continuous nowadays [64; 65]. The EOs of aromatic and medicinal plants is a great source of antimicrobial and food preservative compounds [66]. EOs have been proposed for many applications, such as postharvest antifungal agents, against phytopathogenic bacteria, food preservatives, or even as compounds in active packaging [66; 67; 68; 69]. Antimicrobial activity might be attributed to EO synthesis rich in terpenoids, alcoholic compounds, ketogenic bodies, phenols, aromatic phenols, and other secondary plant metabolites [66].The main \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{_Streptococcus mutans_} & \multicolumn{2}{c}{_Candida albicans_} \\ \hline  & **MIC \% \(v\)/\(v\)** & **MBC \% \(v\)/\(v\)** & **MIC \% \(v\)/\(v\)** & **MFC \% \(v\)/\(v\)** \\ \hline Hydrosol & 25 & 30 & 35 & 35 \\ _O. vulgare_ ssp. _hitrum_ & ND & ND & ND & ND \\ \hline Hydrosol & ND & ND & ND & ND \\ _S. officinalis_ & ND & ND & ND & ND \\ \hline Hydrosol & ND & ND & ND & ND \\ _M. pulgeium_ & ND & ND & ND & ND \\ \hline Essential oil & & & & \\ _O. vulgare_ ssp. _hitrum_ & 0.05 & 0.05 & 0.05 & 0.05 \\ \hline Essential oil & & & & \\ _S. officinalis_ & 0.25 & 0.35 & 0.40 & \textgreater{}0.5 \\ \hline Essential oil & & & & \\ _M. pulgeium_ & 0.45 & 0.45 & 0.25 & 0.25 \\ \hline Carvacrol (98\%) & 0.0315 & 0.0315 & 0.0175 & 0.0315 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: MIC, MBC and MFC results. ND: Not determined. issue regarding the application of EOs in the health, agriculture, cosmetics, and food industries is the compound volatility EOs extracted from the same herbal species, which might have a different chemical synthesis depending on the extraction method, climate diversity, or even seasonal variation [14,70]. Oregano EO exerted the highest antimicrobial activity. The very high antifungal activity of oregano EO against _C. albicans_ compared to other EOs like cinnamon, thyme, and ginger, has been demonstrated in a previous study, whereas MIC and MFC values were ranging from 200 to 800 \(\upmu\)g/mL regarding 60 _C. albicans_ isolates (30 resistant and 30 susceptible to funconazole), which are comparable to our results [71]. Our findings demonstrated the high antimicrobial activity exerted by carvacrol, present in oregano essential oil.