## 4 Discussion
### Investigation of Interaction of LIN with Selected Antifungal Agents  
The anti-_Candida_ activity of LIN may also be exploited using new therapeutic strategies such as combination approach, which is an effective trend in fighting invasive fungal infections [59]. It takes different beneficial characteristics associated with each combined product by improving the efficacy of the individual components. Moreover, in the context of a multi-ingredient combination (of two or more compounds), active compounds may have various mechanisms of action and target sites in the fungal cells. This may enhance the desired antifungal effect, most likely by synergistic and/or additive interactions [7; 45; 59]. In the case of synergism (synergy), the combination of these substances is much more effective than each compound separately [45]. The combined preparation may also have lower toxicity and fewer side effects due to the reduced concentration of individual ingredients [61]. An appropriate mixing of antimycotics can provide a broader antifungal effect and potentially reduce the risk of resistance in fungi [62; 63]. The strategy involving the combination of plant component with conventional antifungals has given encouraging results in recent times. Hence, the antifungal potential of LIN in combination with six different antimycotics was further analyzed by us for the possible synergistic interactions. These studies were carried out in vitro toward _C. albicans_ ATCC 10231. _C. albicans_ is most often isolated from superficial infections, among others from skin or mucous membrane, oral candidiasis, and also endodontic, periodontal or peri-implant infections [64]. Therefore, this species was used for our study. As for the clinical use of LIN, it is considered as an agent applied in oral hygiene and dentistry (as component of mouthwashes). It is also suggested that its combination with certain antimycotics used in oral candidiasis may enhance the efficacy of both. In addition, for superficial candidiasis, a topical antifungal agent is preferred for better activity due to a greater penetration of the drug and to avoid systemic side effects [64]. In these studies, we assessed the interactions between LIN and a selected antibiotic, i.e., nystatin, and some antiseptics--cetylpyridinium, chlorquinaldol, chlorhexidine, silver nitrate and triclosan--to evaluate their potential synergistic effect with each other. These compounds are used as antimicrobial agents both in the prevention or treatment of surface and oral infections and in professional oral hygiene. They are components of many oral care preparations, such as mouthwashes and dentifrices, as well as dental hygiene products [4; 4; 65; 61; 66; 67]. Our results indicated a promising effect of the combination of LIN with the above antimyctics and confirmed three types of interactions, namely synergism, addition, and indifference. It should be noted that the combined concentrations of the two main components needed to eliminate _C. albicans_ were lower. The MIC value of LIN alone was 8000 \(\mathrm{\SIUnitSymbolMicro g}\)/mL, and in the combination, the value decreased 2-16-fold depending on the antimycotic. Similarly, the MICs of antifungals decreased from 2- to 16-fold (except nystatin). The combinations involving LIN with cetylpyridinium, chlorhexidine, or triclosan were a good idea due to the lowest FICIs (0.3125 or 0.375) and synergistic interactions. Of these, the most favorable combination was shown for terpene with chlorhexidine (FICI = 0.3125). Their MICs were reduced even 4-16 times. The synergistic effect can be related to different target sites and mechanisms of action, which enhances their anticandidal effect. The mode of activity of LIN was previously described in detail (the interaction with the ergosterol in cell membrane). Chlorhexidine, on the other hand, can bind to proteins in the cell wall and lead to a loss of cell integrity, followed by a leakage of cellular constituents [65]. These results suggested that the combined activity of LIN and chlorhexidine toward _C.