*3.5. Assay of the Antimicrobial Activity*

The antimicrobial (antibacterial and antifungal) activity of BBEs was tested against four bacteria and three fungi, selected based on their relevance for public health. *Staphylococcus aureus* was the most sensitive strain towards all tested samples, with similar values of MIC (1.56 mg/mL) and MBC (3.12 mg/mL) (Table 6). Additionally, all tested extracts showed a good antibacterial activity on *E. coli, P. aeruginosa*, and *S. typhimurium* strains (MIC—3 mg/mL, and MBC—6 mg/mL).

The antibacterial activity of phenolic compounds has been demonstrated in various studies [4,6]. The previous study of the aqueous beech bark extract, underlined the antimicrobial activity against methicillin-resistant *S. aureus* [11].

Concerning the antifungal activity of the samples (Table 7), all tested *Candida* species, exhibited the highest sensitivity to aqueous extract of beech bark (BBE1) with 25 mg/mL MIC and 50 mg/mL MFC (Table 7). The effect of ethanolic extracts (BBE2, BBE3) on *Candida* species was absent at a concentration of 50 mg/mL.

Thus, the antibacterial activity of BBE could be attributed at least in part to phenolic compounds.


**Table 6.** Antibacterial activity (mg/mL) of the beech bark extracts (BBE).

Notes: BBE1—extracts obtained with water 100%, BBE2—extracts obtained with ethanol–water 50:50, BBE3—extracts obtained with ethanol–water 80:20.


**Table 7.** Antifungal activity (mg/mL) of the beech bark extracts (BBE).

Notes: BBE1—extracts obtained with water 100%, BBE2—extracts obtained with ethanol–water 50:50, BBE3—extracts obtained with ethanol–water 80:20.
