Antimicrobial Activity of Ethanolic and Methanolic Extracts of Urtica dioica, Mentha longifolia, and Bacteriocin Produced by Lactobacillus casei Against Antibiotic-Resistant Bacteria

Background: The increasing resistance of human microbial pathogens to the available antibacterial compounds is a significant threat, resulting in the search for new antibiotic resources such as plants and probiotics. Therefore, this study aimed to evaluate the antibacterial effect of ethanolic and methanolic extracts of Urtica dioica, Mentha longifolia, and bacteriocin purified from a probiotic bacteria using the standard disk diffusion method against some pathogenic strains. Materials and methods: Ethanolic/methanolic extract of U. dioica, M. longifolia, and bacteriocin from probiotic bacteria were prepared by the standard methods. The effect of different concentrations of the extracts on some antibiotic-resistant bacteria was evaluated using the standard disk diffusion method by measuring the diameter of the growth inhibition zone. Results: The disk diffusion test showed that the bacteriocin Lactobacillus casei had more growth inhibitory effects on the tested bacterial strains than the methanolic and ethanolic extracts of U. dioica and M. longifolia. Bacteriocin extract of L. casei exhibited significant antibacterial activity at the concentrations of 12 and 18 mg/mL (P≤0.05) against antibiotic-resistant bacteria, while a 12 mm zone of inhibition was observed in the concentration of 1.5 mg/mL against Salmonella enterica serovar Typhimurium (S. Typhimurium). Conclusion: According to the agar well diffusion method results, the bacteriocin producing L. casei has an extensive range of antibacterial spectrum against resistant bacteria. It can be used as an alternative to antimicrobia agents for the treatment of infections caused by resistant bacteria. It is suggested that in future research, the cytotoxicity of the extracts be evaluated in vitro/in vivo studies.