## 3 Results and Discussion
### Antimicrobial Activity  
The MIC and MCC values obtained with the AM or the solvent alone (EtOH) were reported in Table 7. The correspondence of the sensitivity obtained by testing the two compounds indicates that the inhibitory and cytocidal activity is given by the presence of EtOH and not by the active ingredients extracted from spirulina. The most susceptible strains were those of _K. pneumoniae_ and _C. aureus_ (MCC = 3.12% \(v/v\)), while the most resistant was that of _E. faecalis_ (MCC = 25% \(v/v\)). To date, neither the mechanisms of action nor the active ingredients responsible for the antimicrobial activity are known in the literature. To better illustrate the prebiotic effects induced by scalar dilutions of AM, the growth curves of the bacteria _L. rhamnus_, _L. casei_ and _Saccharomyces boulardii_ are shown in Figures 1-3. \begin{table}
\begin{tabular}{c c c} \hline  & **ABTS\({}^{**}\)** & **FRAP** \\  & **mmol TE/g DW** & **mmol Fe\({}^{2+}\)E/g DW** \\ \hline PBS & 5.96 \(\pm\) 0.13 1  & 5.28 \(\pm\) 0.29 1  \\ \hline MetOH 80\% & 0.92 \(\pm\) 0.05 2  & 4.34 \(\pm\) 0.30 2  \\ \hline FRAP: ferric reducing antioxidant power. ABTS\({}^{**}\)**: radical scavenging activity assays. TE: & **Trolox equivalent. Data are means \(\pm\) standard deviation of three (\(n=3\)) replicates. Means with different letters in the same column are significantly different (Student \(t\)-test, \(p<0.05\)).[ENDFOOTNOTE] \\ \hline \end{tabular}
\end{table} 
Table 6: TAC values. \begin{table}
\begin{tabular}{c c c c c} \hline  & **MIC 1 (\% \(v/v\))** & \multicolumn{2}{c}{**MCC 2 (\% \(v/v\))**} \\ \hline
**Bacterial Strain** & **AM** & **EtOH** & **AM** & **EtOH** \\ \hline _S. aureus_ & 3.12 & 3.12 & 12.5 & 12.5 \\ _E. coli_ & 1.56 & 1.56 & 6.25 & 6.25 \\ _P. aeruginosa_ & 3.12 & 3.12 & 6.25 & 6.25 \\ _K. pneumoniae_ & 0.78 & 0.78 & 3.12 & 3.12 \\ _E. faecalis_ & 1.56 & 3.12 & 25 & 25 \\ _C. albicans_ & 1.56 & 1.56 & 3.12 & 3.12 \\ \hline \end{tabular}
\end{table} 
Table 7: MIC and MCC values. In detail, Figure 1 illustrates the growth curves of _S. boulardii_ in the presence of scalar dilutions of the AM. A rigorous statistical analysis reveals that concentrations below 6.25% \(v/v\) have no discernible impact on yeast growth. Conversely, treatments with  
Figure 1: Growth curves of _S. boulardi_ in the presence of scalar dilutions of the AM. The control is indicated with the dotted line. Figure 3: Growth curves of _L. casei_ in the presence of scalar dilutions of the AM. The control is indicated with the dotted line. (***\(p<0.0005\)). Figure 2: Growth curves of _L. rhamnous_ in the presence of scalar dilutions of the AM. The control is indicated with the dotted line. concentrations equal to or exceeding 6.25% \(v/v\) significantly inhibit growth, demonstrating statistical significance at \(p<\) 0.0001. Although _L. rhamnus_ shows a positive growth trend when incubated in the presence of AM concentrations lower than 0.78% \(v/v\) (Figure 2--boxed values), it also does not show statistically significant variations if compared to the positive control. On the contrary, AM concentrations greater than 12.5% \(v/v\) are toxic. The _L. casei_ strain has a different trend from previous strains. In fact, it is possible to identify three different activities of the various AM concentrations tested. Specifically, data show the following actions: toxic for concentrations equal to 25% \(v/v\) and 12.5% \(v/v\), growth promoter (boxed values--\(p<\) 0.0005) for concentrations equal to 3.12% \(v/v\) and 1.56% \(v/v\), and irrelevant for all other concentrations. The data show that the anti-microbial activity detected against pathogenic strains is due exclusively to the ethanol content and not to the active ingredients extracted from the algae. On the contrary, some probiotic strains widely distributed on the market and used to produce functional foods, such as milks or fermented milks, are stimulated in the presence of low concentrations of this extract.