Antibacterial effects of Zataria multiflora and Eucalyptus camaldulensis extracts versus 0.2% chlorhexidine on Streptococcus mutans count: an in vitro study

Chlorhexidine (CHX) is the most widely used synthetic antibacterial mouthwash to decrease the count of certain microorganisms. However, considering its side effects, this study aimed to compare the antibacterial effects of Zataria multiflora (Z. multiflora) and Eucalyptus camaldulensis (E. camaldulensis) extracts with 0.2% CHX on Streptococcus mutans (S. mutans) count. In this in vitro experimental study, Z. multiflora and E. camaldulensis extracts were first obtained. The diameter of the growth inhibition zones of S. mutans in the presence of 10,000 and 50,000 ppm concentrations of the extracts and 0.2% CHX was then recorded in an agar well diffusion test; 0.2% CHX mouthwash served as the positive control, and distilled water served as the negative control. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the extracts, and 0.2% CHX were also determined against S. mutans. Moreover, the S. mutans count was measured before and after exposure to the extracts, and 0.2% CHX was compared. Data were analyzed by SPSS 26.0. The agar well diffusion test revealed that the diameter of the growth inhibition zones caused by Z. multiflora and E. camaldulensis extracts, and 0.2% CHX was 10 mm, 10 mm, and 13 mm, respectively for 10,000 ppm concentration, and 18 mm, 22 mm, and 23 mm for 50,000 ppm concentration, respectively. The MIC of 0.2% CHX, E. camaldulensis extract, and Z. multiflora extract was 2500, 2500, and 5000 ppm, respectively, and their MBC was 20,000, 10,000 and, 10,000 ppm, respectively. E. camaldulensis extract caused a greater reduction in S. mutans colony count than Z. multiflora and 0.2% CHX. The results revealed significant antibacterial activity of Z. multiflora and E. camaldulensis extracts against S. mutans. It appears that E. camaldulensis may be suitable for incorporation in the formulation of mouthwashes given that its optimal biocompatibility and lack of cytotoxicity are confirmed in future studies.