3.3.6. Antibacterial Activity against *S. mutans* and *P. intermedia*

*Streptococcus mutans* and *Prevotella intermedia* are the main causative agents of periodontal diseases and are known for their resistance [59–61]. According to Eloff [22] and van Vuuren [62], an extract with an MIC lower than 8 mg/mL is considered to have some antimicrobial activity, while extracts having an MIC below 1 mg/mL are considered worth exploring further. The *S. perfoliata* extract in the present study, showed low antibacterial activity for *S. mutans* and moderate activity for *P. intermedia* with MICs of 6.25 mg/mL and 3.125 mg/mL respectively.

The essential oils of some members of the *Sideritis spp.* namely; *S. curvidens* and *S. lanata* were reported to have high antimicrobial activity against *S. mutans*, using the disc diffusion method. The zones of inhibition measured at 22 mm for *S. curvidens* and 23 mm for *S. lanata* using 25 μL of essential oil [63]. There were no previous reports of the activity of *S. perfoliata* on either of the microorganisms tested in the present study, providing new knowledge on the antibacterial activity of the examined species.
