Antibacterial and Drug Synergistic Activities of Mentha longifolia Essential Oil Against Shigella flexneri and Shigella sonnei

Background: Microbial infections such as shigellosis are one of the major health challenges in Iran, especially in Khuzestan province in the south west of Iran. Objective: According to the importance of medicinal plants in the treatment of many infectious diseases, and as a valuable alternative for antibiotics, the aim of this research was to assess the antibacterial and drug synergistic activities of the essential oil from Mentha longifolia, a local plant, against Shigella flexneri and Shigella sonnei as the main causes of shigellosis. Materials and Methods: The M. longifolia essential oil was extracted from the leaves. The antibacterial activities of the essential oil against clinical and standard S. flexneri and S. sonnei strains were detected by the disk diffusion and micro-broth dilution methods. Results: The essential oil of M. longifolia had the most significant antibacterial activity against the clinical strain of S. flexneri. Minimum inhibitory concentration (MIC) of 1024 with a concentration of 0.8 mg/mL of essential oil was detected in both the standard and clinical S. flexneri and S. sonnei strains. The essential oil of M. longifolia showed the highest synergistic effect on gentamicin and ampicillin in the clinical isolates of S. flexneri. Conclusion: The results of this study showed that the essential oil of M. longifolia alone or in combination with antimicrobial agents may be useful in the treatment of bacterial infections. In addition, M. longifolia may increase the effect of antibiotics and resolve other antibiotic resistance problems.