Antibacterial effects of the aqueous extract of Lycopersicon esculentum mill native to South Khorasan of Iran against four species of gastrointestinal bacterial pathogens

Introduction: Raising antibiotic resistance has led the human community to more frequent application of herbal medicines. The tomato fruit, scientifically called Lycopersicon esculentum mill, is an important source of vitamins, minerals, and antioxidants, all with beneficial effects on human health. The present study aimed to evaluate the antibacterial effects of tomato aqueous extract on four species of common bacteria associated with gastrointestinal infections. Materials and methods: After preparing the aqueous extract of native tomato, its minimum inhibitory concentration (MIC) was determined against Staphylococcus aureus (S. aureus) (TCC116538), Klebsiella pneumonia (K. pneumonia) (ATCC700603), Shigella flexneri (S. flexneri) (ATCC12022), and Proteus vulgaris (ATCC6380) species using micro dilution broth method based on the Clinical and Laboratory Standards Institute guidelines. Each of the experiments was repeated three times. The results were subdivided into normal and abnormal variables by one-sample Kolmogorov-Smirnov test. One-way Analysis of Variance (ANOVA) was used for examining normal variables. Results: The results of this study showed that the most significant effect of the tomato extract is on S. aureus. The MIC of tomato extract for S. aureus was 31.25 mg/ml, while for Proteus vulgaris, K. pneumoniae, and S. flexneri was 62.5 mg/ml. The mean MIC of the extract was significantly different between the studied bacteria (P < 0.05). The LSD post hoc test showed that the MIC for S. aureus (0.0599 ± 0.001) was significantly higher than that of Shigella flexinari (S. flexneri) (0.351 ± 0.009) (P < 0.001), K. pneumoniae (0.469 ± 0.062) (P = 0.001), and Proteus vulgaris (0.492 ± 0.005) (P = 0.003). Moreover, the MIC for S. flexneri was significantly lower than that of K. pneumoniae (P = 0.002) and Proteus vulgaris (P = 0.001). The mean MIC values for K. pneumoniae and Proteus vulgaris (P = 0.394) were not significantly different. Conclusion: The current study revealed a significant antibacterial effect of tomato extract against different bacterial species. Therefore, the extract can be used as an antiseptic agent in pharmaceutical and food industries.