Evaluation of synergistic antimicrobial activity of silver nanoparticles and Eucalyptus microtheca on streptococcus mutans

Streptococcus mutans is a main bacteria caused by tooth decay. In the present study, antibacterial activities of the essential oil and hydroalcoholic extract of EucalyptusMicrotheca and silver nanoparticles (Ag NPs) as compared to some different standard antibiotics, was evaluated against S. mutans.

In this experimental study, bactericidal activities of the mentioned essential oil, extract, Ag NPs, and the selected antibiotics including Amoxicillin-Clavulanic acid, Chloramphenicol, and Ciprofloxacin were evaluated using the agar disc diffusion method against S. mutans. The main bioactive compounds presented in the essential oil and extract of E. microtheca were detected using gas chromatography technique (GC-MS). All the obtained results were statistically analyzed using SPSS software and the comparison test using Dunken with 95% of significance level was used.

The results obtained indicated that maximum clear zone area with diameter of 23±0.2 mm was observed for the samples containing essential oil and extract of E. microtheca  and Ag NPs. While the minimum clear zone (7±0.1 mm) war related to the sample containing essential oil of E. microtheca and Ag NPs. The results also indicated that the clear zone diameter for the samples containing Amoxicillin-Clavulanic acid, Chloramphenicol, and Ciprofloxacin were 8±0.1, 22±0.2 and 9±0.1 mm, respectively. GC-MS analysis indicated that there were 44 bioactive compounds in the essential oil of E. microtheca which Eucalyptol, alpha-Pinene and L-trans- Pinocarol were the most important components. Furthermore, the extract of E. microtheca was contained 30 bioavtive compounds which Eucalyptol, Globulol and Aroman dendron were its main components.

The results showed that silver nanoparticles in combination with extract and essential oil of E. microtheca have antimicrobial activity against S. mutans.