Evaluation of Synergistic Antibacterial Effect of Combined Scrophularia striata Extract and Antibiotics Against Pseudomonas aeruginosa and Methicillin -Resistant Staphylococcus aureus

Scrophularia. striata from Scrophulariacea family has been used in Iranian folk medicine for the treatment of infectious diseases. In this study we evaluated the synergistic effect of S. striata hydroalcoholic extract (SSE) and commercially available antibiotics against P. aeroginosa and Methicillin- resistant Staphylococcus aureus (MRSA). The resazurin-based microdilution method was used to determine the minimum inhibitory concentration (MIC) values of plan extract and standard antibiotics. The interaction between standard antibiotics and SSE was evaluated by using checkerboard method. The results of this study revealed that SSE enhance the antibacterial activity of antibiotics. The combination of SSE and Vancomycin had synergistic to additive effects against MRSA. SSE in combination with Gentamicin had synergistic to additive effects against P. aeruginosa. The interaction between Ceftazidime and SSE was additive against P. aeruginosa. The best result was the synergistic effect between SSE and Piperacillin-Tazobactam against P. aeruginosa. In conclusion the results of this research indicated that S. striata has the potential to enhance the antibacterial activity of antibiotics and could be a source to the designing new compounds with synergistic effect in combination with standard antibiotics.