## 3 Results
### Evaluation of Interaction of LIN with Selected Antifungal Agents  
In the next step of our studies, the effect of the combination of terpene with nystatin and some antiseptics--chlorquinaldol, cetylpyridinium, chlorhexidine, silver nitrate and triclosan--on the growth of one of the reference strains, i.e., _C. albicans_ ATCC 10231, was evaluated. _C. albicans_ is most often isolated from candidiasis, so it was used for further research. The potential interactions of LIN with antifungals listed above were determined using the checkerboard technique. MICs of LIN and studied antimycotics alone, as well as their MICs in combinations, were used to calculate fractional inhibitory concentration (FIC) and FIC index (FICI, \(\Sigma\) FIC) values, which were then accordingly interpreted [32]. The data shown in Table 3 and Figure 3 present three different types of interactions between LIN and studied antifungals: synergy, addition, and indifference toward _C. albicans_. Notably, no antagonism was found. The MIC value of LIN alone was 8000 \(\mathrm{\SIUnitSymbolMicro g}\)/mL, while in the combination, its MICs were reduced to 2-16-fold depending on the antimycotic. The MICs of the antifungals in the combination also decreased. Combining LIN with some antiseptics was a very good idea. LIN showed beneficial synergistic interactions with cetylpyridinium, chlorhexidine, and triclosan against studied strains. FICI values were in the range 0.3125-0.375. The most favorable combination was shown for terpene with chlorhexidine (FICI = 0.3125). The MIC values of LIN and this antiseptic alone were reduced even 16 and 4 times in combination, from 8000 \(\mathrm{\SIUnitSymbolMicro g}\)/mL to 500 \(\mathrm{\SIUnitSymbolMicro g}\)/mL (FIC = 0.0625) and from 7.81 \(\mathrm{\SIUnitSymbolMicro g}\)/mL to 1.95 \(\mathrm{\SIUnitSymbolMicro g}\)/mL (FIC = 0.25), respectively (Table 3, Figure 3b). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Antifungal Agent**} & \multicolumn{2}{c}{**MIC of Antifungal Agent (\(\mathrm{\SIUnitSymbolMicro g}\)/mL)**} & \multirow{2}{*}{**\(p\) ***} & \multirow{2}{*}{**FIC**} & \(\mathbf{\Sigma\) **FIC**} & \multirow{2}{*}{**Interpretation**} \\ \cline{2-2} \cline{5-6}  & **Alone** & & & & & \\ \hline LIN & 8000 & 500 & 0.012 & 0.0625 & \\ nystatin & 0.48 & 0.48 & 0.917 & 1 & 1.0625 & \\ \hline LIN & 8000 & 1000 & 0.016 & 0.125 & \\ cetylpyridinium & 3.91 & 0.98 & 0.012 & 0.25 & \\ \hline LIN & 8000 & 500 & 0.012 & 0.0625 & \\ chlorhexidine & 7.81 & 1.95 & 0.012 & 0.25 & \\ \hline LIN & 8000 & 4000 & 0.175 & 0.5 & \\ chlorquinaldol & 0.98 & 0.48 & 0.060 & 0.5 & \\ \hline LIN & 8000 & 1000 & 0.016 & 0.125 & \\ silver nitrate & 7.81 & 3.91 & 0.060 & 0.5 & \\ \hline LIN & 8000 & 1000 & 0.012 & 0.125 & \\ triclosan & 7.81 & 1.95 & 0.012 & 0.25 & \\ \hline \hline \end{tabular}  
* Mann–Whitney U test.  
\end{table} 
Table 3: The effect of the combination of LIN with selected antimycotics against _C. albicans_ ATCC 10231. In the case of the combination of LIN with cetylpyridinium or triclosan, synergism at FICI = 0.375 was observed. The MIC of terpene was also reduced 8-fold in the combination with both of the antisetics compared to its MIC alone (from 8000 \(\upmu\)g/mL to 1000 \(\upmu\)g/mL, FIC = 0.125). In turn, MICs of cetylpyridinium and triclosan decreased 4 times, from 3.91 \(\upmu\)g/mL to 0.98 \(\upmu\)g/mL and from 7.81 \(\upmu\)g/mL to 1.95 \(\upmu\)g/mL, respectively. The FIC values were the same--0.25 (Table 3, Figure 3a,c). Moreover, an addition interaction of LIN in combination with chlorquinaldol (FICI = 1) and silver nitrate (FICI = 0.625) was indicated. _C. albicans_ strains were 2- and 8-fold  
Figure 3: Isobolograms indicating the synergy of linabol (LIN) with (a) cetylpyridinium (CET), (b) chlorhexidine (CHX), and (c) triclosan (TRC) for _C. albicans_ ATCC 10231.  
more sensitive to LIN in combination with these antifungals, respectively.