## 4 Discussion
### Investigation of Interaction of LIN with Selected Antifungal Agents
albicans_ was higher than their action alone. The reduced concentration of LIN and chlorhexidine (required to treat infections) in such a mixture will reduce their side effects (especially chlorhexidine, i.e., tooth discoloration, burning sensation or bitter taste) [65]. Additionally, the combination of LIN with either cetylpyridinium or triclosan increased their anticandidal efficacy 4-8 times with identical FICIs of 0.375. Most likely, the mechanism of action of cetylpyridinium can also increase LIN activity. This compound affects the cell by disturbing its simoregulation and homeostasis. As a result, there may be a leakage of K\({}^{+}\) and pentose from the cells as well as autolysis through the activation of intracellular latent ribonucleases. There is also a breakdown of membranes, the leakage of the contents from cytoplasm, damage to nucleic acids and proteins, and the lysis of the cell wall by autolytic enzymes [66]. In the case of triclosan, K\({}^{+}\) leakage occurs, which indicates membrane damage, inhibition of ATP-ase enzyme activity, membrane destabilization, impaired ion transport, and the modulation of overall cellular osmoregulation [42]. This may enhance the anticandidal activity of LIN when combined with triclosan. Moreover, the additive interaction between LIN and silver nitrate (FICI = 0.625) or chlorquinaldol (FICI = 1) was observed. _C. albicans_ strains were 8- and 2-fold more susceptible to LIN in combination with these antiseptics, respectively. Single studies report that silver nitrate exhibits antifungal activity probably by destroying membrane integrity. However, the more detailed mechanisms of the antifungal action of this antiseptic still need to be determined [67]. In the case of chlorquinaldol, it is presumed that it uses its lipophilicity to penetrate cell membranes, where its antimicrobial activity is probably related to its chelating activity [68]. Perhaps these properties of silver nitrate and chlorquinaldol also enhanced the antifungal effect of LIN. In turn, the LIN-nystatin combination indicated an indifference interaction by showing an FICI of 1. This is also a beneficial action where both components can be combined. However, it would not be advisable to lower their concentration. Both LIN and nystatin can affect the cell in a similar way. Nystatin binds to ergosterol in the membrane, causing changes in membrane permeability that allow the release of K\({}^{+}\), metabolites, and sugars. It is believed that cell membrane damage is responsible for fungal death [69]. There are no studies in the literature investigating the interaction of LIN with these antifungal agents. Our previous data [4] on the effect of the combination of eugenol (EUG) and clove essential oil (CEO) with selected antimycotics showed their good effect toward four reference _Candida_ spp. strains (_C. albicans_, _C. Krusei_, _C. glabrata_, and _C. parapsilosis_). It was these results that encouraged us to continue research on LIN. Both CEO and EUG indicated synergy with cetylpyridinium. Their MIC values after the combination decreased 4-8 fold. A similar post-combination activity was also found for them with chlorhexidine (synergy and addition). When these component were combined with silver nitrate or triclosan, a 2-8-fold reduction in their MICs and synergism or addition against _Candida_ spp. were also observed. In all cases, synergism with a similar FICI = 0.375-0.5 was shown. The indifference, as in these studies, was found only in combination with nystatin (FICI = 1.25-1.5). However, few reports present the results of the interaction of LIN with other compounds. Particularly noteworthy are the results presented by [PERSON] et al. [16], which indicated interactions of LIN with geraniol and Gluconazole (FLC) toward both _C. albicans_ and _C. neoformans_ isolates. The synergy was showed in the combination of LIN with geraniol (FICI = 0.284-0.38 for _C. albicans_ strains). Their MIC values were reduced 4-32 times.